Math::BigInt(3p)Perl Programmers Reference Guide Math::BigInt(3p)NAMEMath::BigInt - Arbitrary size integer/float math package
SYNOPSIS
use Math::BigInt;
# or make it faster: install (optional) Math::BigInt::GMP
# and always use (it will fall back to pure Perl if the
# GMP library is not installed):
use Math::BigInt lib => 'GMP';
my $str = '1234567890';
my @values = (64,74,18);
my $n = 1; my $sign = '-';
# Number creation
$x = Math::BigInt->new($str); # defaults to 0
$y = $x->copy(); # make a true copy
$nan = Math::BigInt->bnan(); # create a NotANumber
$zero = Math::BigInt->bzero(); # create a +0
$inf = Math::BigInt->binf(); # create a +inf
$inf = Math::BigInt->binf('-'); # create a -inf
$one = Math::BigInt->bone(); # create a +1
$one = Math::BigInt->bone('-'); # create a -1
# Testing (don't modify their arguments)
# (return true if the condition is met, otherwise false)
$x->is_zero(); # if $x is +0
$x->is_nan(); # if $x is NaN
$x->is_one(); # if $x is +1
$x->is_one('-'); # if $x is -1
$x->is_odd(); # if $x is odd
$x->is_even(); # if $x is even
$x->is_pos(); # if $x >= 0
$x->is_neg(); # if $x < 0
$x->is_inf($sign); # if $x is +inf, or -inf (sign is default '+')
$x->is_int(); # if $x is an integer (not a float)
# comparing and digit/sign extration
$x->bcmp($y); # compare numbers (undef,<0,=0,>0)
$x->bacmp($y); # compare absolutely (undef,<0,=0,>0)
$x->sign(); # return the sign, either +,- or NaN
$x->digit($n); # return the nth digit, counting from right
$x->digit(-$n); # return the nth digit, counting from left
# The following all modify their first argument. If you want to preserve
# $x, use $z = $x->copy()->bXXX($y); See under L<CAVEATS> for why this is
# neccessary when mixing $a = $b assigments with non-overloaded math.
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$x->bzero(); # set $x to 0
$x->bnan(); # set $x to NaN
$x->bone(); # set $x to +1
$x->bone('-'); # set $x to -1
$x->binf(); # set $x to inf
$x->binf('-'); # set $x to -inf
$x->bneg(); # negation
$x->babs(); # absolute value
$x->bnorm(); # normalize (no-op in BigInt)
$x->bnot(); # two's complement (bit wise not)
$x->binc(); # increment $x by 1
$x->bdec(); # decrement $x by 1
$x->badd($y); # addition (add $y to $x)
$x->bsub($y); # subtraction (subtract $y from $x)
$x->bmul($y); # multiplication (multiply $x by $y)
$x->bdiv($y); # divide, set $x to quotient
# return (quo,rem) or quo if scalar
$x->bmod($y); # modulus (x % y)
$x->bmodpow($exp,$mod); # modular exponentation (($num**$exp) % $mod))
$x->bmodinv($mod); # the inverse of $x in the given modulus $mod
$x->bpow($y); # power of arguments (x ** y)
$x->blsft($y); # left shift
$x->brsft($y); # right shift
$x->blsft($y,$n); # left shift, by base $n (like 10)
$x->brsft($y,$n); # right shift, by base $n (like 10)
$x->band($y); # bitwise and
$x->bior($y); # bitwise inclusive or
$x->bxor($y); # bitwise exclusive or
$x->bnot(); # bitwise not (two's complement)
$x->bsqrt(); # calculate square-root
$x->broot($y); # $y'th root of $x (e.g. $y == 3 => cubic root)
$x->bfac(); # factorial of $x (1*2*3*4*..$x)
$x->round($A,$P,$mode); # round to accuracy or precision using mode $mode
$x->bround($n); # accuracy: preserve $n digits
$x->bfround($n); # round to $nth digit, no-op for BigInts
# The following do not modify their arguments in BigInt (are no-ops),
# but do so in BigFloat:
$x->bfloor(); # return integer less or equal than $x
$x->bceil(); # return integer greater or equal than $x
# The following do not modify their arguments:
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# greatest common divisor (no OO style)
my $gcd = Math::BigInt::bgcd(@values);
# lowest common multiplicator (no OO style)
my $lcm = Math::BigInt::blcm(@values);
$x->length(); # return number of digits in number
($xl,$f) = $x->length(); # length of number and length of fraction part,
# latter is always 0 digits long for BigInts
$x->exponent(); # return exponent as BigInt
$x->mantissa(); # return (signed) mantissa as BigInt
$x->parts(); # return (mantissa,exponent) as BigInt
$x->copy(); # make a true copy of $x (unlike $y = $x;)
$x->as_int(); # return as BigInt (in BigInt: same as copy())
$x->numify(); # return as scalar (might overflow!)
# conversation to string (do not modify their argument)
$x->bstr(); # normalized string (e.g. '3')
$x->bsstr(); # norm. string in scientific notation (e.g. '3E0')
$x->as_hex(); # as signed hexadecimal string with prefixed 0x
$x->as_bin(); # as signed binary string with prefixed 0b
# precision and accuracy (see section about rounding for more)
$x->precision(); # return P of $x (or global, if P of $x undef)
$x->precision($n); # set P of $x to $n
$x->accuracy(); # return A of $x (or global, if A of $x undef)
$x->accuracy($n); # set A $x to $n
# Global methods
Math::BigInt->precision(); # get/set global P for all BigInt objects
Math::BigInt->accuracy(); # get/set global A for all BigInt objects
Math::BigInt->round_mode(); # get/set global round mode, one of
# 'even', 'odd', '+inf', '-inf', 'zero' or 'trunc'
Math::BigInt->config(); # return hash containing configuration
DESCRIPTION
All operators (inlcuding basic math operations) are over-
loaded if you declare your big integers as
$i = new Math::BigInt '123_456_789_123_456_789';
Operations with overloaded operators preserve the arguments
which is exactly what you expect.
Input
Input values to these routines may be any string, that
looks like a number and results in an integer, including
hexadecimal and binary numbers.
Scalars holding numbers may also be passed, but note that
non-integer numbers may already have lost precision due to
the conversation to float. Quote your input if you want
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BigInt to see all the digits:
$x = Math::BigInt->new(12345678890123456789); # bad
$x = Math::BigInt->new('12345678901234567890'); # good
You can include one underscore between any two digits.
This means integer values like 1.01E2 or even 1000E-2 are
also accepted. Non-integer values result in NaN.
Currently, Math::BigInt::new() defaults to 0, while
Math::BigInt::new('') results in 'NaN'. This might change
in the future, so use always the following explicit forms
to get a zero or NaN:
$zero = Math::BigInt->bzero();
$nan = Math::BigInt->bnan();
"bnorm()" on a BigInt object is now effectively a no-op,
since the numbers are always stored in normalized form. If
passed a string, creates a BigInt object from the input.
Output
Output values are BigInt objects (normalized), except for
the methods which return a string (see SYNOPSIS).
Some routines ("is_odd()", "is_even()", "is_zero()",
"is_one()", "is_nan()", etc.) return true or false, while
others ("bcmp()", "bacmp()") return either undef (if NaN
is involved), <0, 0 or >0 and are suited for sort.
METHODS
Each of the methods below (except config(), accuracy() and
precision()) accepts three additional parameters. These
arguments $A, $P and $R are "accuracy", "precision" and
"round_mode". Please see the section about "ACCURACY and
PRECISION" for more information.
config
use Data::Dumper;
print Dumper ( Math::BigInt->config() );
print Math::BigInt->config()->{lib},"\n";
Returns a hash containing the configuration, e.g. the ver-
sion number, lib loaded etc. The following hash keys are
currently filled in with the appropriate information.
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key Description
Example
============================================================
lib Name of the low-level math library
Math::BigInt::Calc
lib_version Version of low-level math library (see 'lib')
0.30
class The class name of config() you just called
Math::BigInt
upgrade To which class math operations might be upgraded
Math::BigFloat
downgrade To which class math operations might be downgraded
undef
precision Global precision
undef
accuracy Global accuracy
undef
round_mode Global round mode
even
version version number of the class you used
1.61
div_scale Fallback acccuracy for div
40
trap_nan If true, traps creation of NaN via croak()
1
trap_inf If true, traps creation of +inf/-inf via croak()
1
The following values can be set by passing "config()" a
reference to a hash:
trap_inf trap_nan
upgrade downgrade precision accuracy round_mode div_scale
Example:
$new_cfg = Math::BigInt->config( { trap_inf => 1, precision => 5 } );
accuracy
$x->accuracy(5); # local for $x
CLASS->accuracy(5); # global for all members of CLASS
# Note: This also applies to new()!
$A = $x->accuracy(); # read out accuracy that affects $x
$A = CLASS->accuracy(); # read out global accuracy
Set or get the global or local accuracy, aka how many signi-
ficant digits the results have. If you set a global accu-
racy, then this also applies to new()!
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Warning! The accuracy sticks, e.g. once you created a number
under the influence of "CLASS->accuracy($A)", all results
from math operations with that number will also be rounded.
In most cases, you should probably round the results expli-
citely using one of round(), bround() or bfround() or by
passing the desired accuracy to the math operation as addi-
tional parameter:
my $x = Math::BigInt->new(30000);
my $y = Math::BigInt->new(7);
print scalar $x->copy()->bdiv($y, 2); # print 4300
print scalar $x->copy()->bdiv($y)->bround(2); # print 4300
Please see the section about "ACCURACY AND PRECISION" for
further details.
Value must be greater than zero. Pass an undef value to dis-
able it:
$x->accuracy(undef);
Math::BigInt->accuracy(undef);
Returns the current accuracy. For "$x-"accuracy()> it will
return either the local accuracy, or if not defined, the
global. This means the return value represents the accuracy
that will be in effect for $x:
$y = Math::BigInt->new(1234567); # unrounded
print Math::BigInt->accuracy(4),"\n"; # set 4, print 4
$x = Math::BigInt->new(123456); # $x will be automatically rounded!
print "$x $y\n"; # '123500 1234567'
print $x->accuracy(),"\n"; # will be 4
print $y->accuracy(),"\n"; # also 4, since global is 4
print Math::BigInt->accuracy(5),"\n"; # set to 5, print 5
print $x->accuracy(),"\n"; # still 4
print $y->accuracy(),"\n"; # 5, since global is 5
Note: Works also for subclasses like Math::BigFloat. Each
class has it's own globals separated from Math::BigInt, but
it is possible to subclass Math::BigInt and make the globals
of the subclass aliases to the ones from Math::BigInt.
precision
$x->precision(-2); # local for $x, round at the second digit right of the dot
$x->precision(2); # ditto, round at the second digit left of the dot
CLASS->precision(5); # Global for all members of CLASS
# This also applies to new()!
CLASS->precision(-5); # ditto
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$P = CLASS->precision(); # read out global precision
$P = $x->precision(); # read out precision that affects $x
Note: You probably want to use accuracy() instead. With
accuracy you set the number of digits each result should
have, with precision you set the place where to round!
"precision()" sets or gets the global or local precision,
aka at which digit before or after the dot to round all
results. A set global precision also applies to all newly
created numbers!
In Math::BigInt, passing a negative number precision has no
effect since no numbers have digits after the dot. In
Math::BigFloat, it will round all results to P digits after
the dot.
Please see the section about "ACCURACY AND PRECISION" for
further details.
Pass an undef value to disable it:
$x->precision(undef);
Math::BigInt->precision(undef);
Returns the current precision. For "$x-"precision()> it will
return either the local precision of $x, or if not defined,
the global. This means the return value represents the prev-
ision that will be in effect for $x:
$y = Math::BigInt->new(1234567); # unrounded
print Math::BigInt->precision(4),"\n"; # set 4, print 4
$x = Math::BigInt->new(123456); # will be automatically rounded
print $x; # print "120000"!
Note: Works also for subclasses like Math::BigFloat. Each
class has its own globals separated from Math::BigInt, but
it is possible to subclass Math::BigInt and make the globals
of the subclass aliases to the ones from Math::BigInt.
brsft
$x->brsft($y,$n);
Shifts $x right by $y in base $n. Default is base 2, used
are usually 10 and 2, but others work, too.
Right shifting usually amounts to dividing $x by $n ** $y
and truncating the result:
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$x = Math::BigInt->new(10);
$x->brsft(1); # same as $x >> 1: 5
$x = Math::BigInt->new(1234);
$x->brsft(2,10); # result 12
There is one exception, and that is base 2 with negative $x:
$x = Math::BigInt->new(-5);
print $x->brsft(1);
This will print -3, not -2 (as it would if you divide -5 by
2 and truncate the result).
new
$x = Math::BigInt->new($str,$A,$P,$R);
Creates a new BigInt object from a scalar or another BigInt
object. The input is accepted as decimal, hex (with leading
'0x') or binary (with leading '0b').
See Input for more info on accepted input formats.
bnan
$x = Math::BigInt->bnan();
Creates a new BigInt object representing NaN (Not A Number).
If used on an object, it will set it to NaN:
$x->bnan();
bzero
$x = Math::BigInt->bzero();
Creates a new BigInt object representing zero. If used on an
object, it will set it to zero:
$x->bzero();
binf
$x = Math::BigInt->binf($sign);
Creates a new BigInt object representing infinity. The
optional argument is either '-' or '+', indicating whether
you want infinity or minus infinity. If used on an object,
it will set it to infinity:
$x->binf();
$x->binf('-');
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bone
$x = Math::BigInt->binf($sign);
Creates a new BigInt object representing one. The optional
argument is either '-' or '+', indicating whether you want
one or minus one. If used on an object, it will set it to
one:
$x->bone(); # +1
$x->bone('-'); # -1
is_one()/is_zero()/is_nan()/is_inf()
$x->is_zero(); # true if arg is +0
$x->is_nan(); # true if arg is NaN
$x->is_one(); # true if arg is +1
$x->is_one('-'); # true if arg is -1
$x->is_inf(); # true if +inf
$x->is_inf('-'); # true if -inf (sign is default '+')
These methods all test the BigInt for beeing one specific
value and return true or false depending on the input. These
are faster than doing something like:
if ($x == 0)
is_pos()/is_neg()
$x->is_pos(); # true if > 0
$x->is_neg(); # true if < 0
The methods return true if the argument is positive or nega-
tive, respectively. "NaN" is neither positive nor negative,
while "+inf" counts as positive, and "-inf" is negative. A
"zero" is neither positive nor negative.
These methods are only testing the sign, and not the value.
"is_positive()" and "is_negative()" are aliase to "is_pos()"
and "is_neg()", respectively. "is_positive()" and
"is_negative()" were introduced in v1.36, while "is_pos()"
and "is_neg()" were only introduced in v1.68.
is_odd()/is_even()/is_int()
$x->is_odd(); # true if odd, false for even
$x->is_even(); # true if even, false for odd
$x->is_int(); # true if $x is an integer
The return true when the argument satisfies the condition.
"NaN", "+inf", "-inf" are not integers and are neither odd
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nor even.
In BigInt, all numbers except "NaN", "+inf" and "-inf" are
integers.
bcmp
$x->bcmp($y);
Compares $x with $y and takes the sign into account. Returns
-1, 0, 1 or undef.
bacmp
$x->bacmp($y);
Compares $x with $y while ignoring their. Returns -1, 0, 1
or undef.
sign
$x->sign();
Return the sign, of $x, meaning either "+", "-", "-inf",
"+inf" or NaN.
If you want $x to have a certain sign, use one of the fol-
lowing methods:
$x->babs(); # '+'
$x->babs()->bneg(); # '-'
$x->bnan(); # 'NaN'
$x->binf(); # '+inf'
$x->binf('-'); # '-inf'
digit
$x->digit($n); # return the nth digit, counting from right
If $n is negative, returns the digit counting from left.
bneg
$x->bneg();
Negate the number, e.g. change the sign between '+' and '-',
or between '+inf' and '-inf', respectively. Does nothing for
NaN or zero.
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babs
$x->babs();
Set the number to it's absolute value, e.g. change the sign
from '-' to '+' and from '-inf' to '+inf', respectively.
Does nothing for NaN or positive numbers.
bnorm
$x->bnorm(); # normalize (no-op)
bnot
$x->bnot();
Two's complement (bit wise not). This is equivalent to
$x->binc()->bneg();
but faster.
binc
$x->binc(); # increment x by 1
bdec
$x->bdec(); # decrement x by 1
badd
$x->badd($y); # addition (add $y to $x)
bsub
$x->bsub($y); # subtraction (subtract $y from $x)
bmul
$x->bmul($y); # multiplication (multiply $x by $y)
bdiv
$x->bdiv($y); # divide, set $x to quotient
# return (quo,rem) or quo if scalar
bmod
$x->bmod($y); # modulus (x % y)
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bmodinv
num->bmodinv($mod); # modular inverse
Returns the inverse of $num in the given modulus $mod.
'"NaN"' is returned unless $num is relatively prime to $mod,
i.e. unless "bgcd($num, $mod)==1".
bmodpow
$num->bmodpow($exp,$mod); # modular exponentation
# ($num**$exp % $mod)
Returns the value of $num taken to the power $exp in the
modulus $mod using binary exponentation. "bmodpow" is far
superior to writing
$num ** $exp % $mod
because it is much faster - it reduces internal variables
into the modulus whenever possible, so it operates on
smaller numbers.
"bmodpow" also supports negative exponents.
bmodpow($num, -1, $mod)
is exactly equivalent to
bmodinv($num, $mod)
bpow
$x->bpow($y); # power of arguments (x ** y)
blsft
$x->blsft($y); # left shift
$x->blsft($y,$n); # left shift, in base $n (like 10)
brsft
$x->brsft($y); # right shift
$x->brsft($y,$n); # right shift, in base $n (like 10)
band
$x->band($y); # bitwise and
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bior
$x->bior($y); # bitwise inclusive or
bxor
$x->bxor($y); # bitwise exclusive or
bnot
$x->bnot(); # bitwise not (two's complement)
bsqrt
$x->bsqrt(); # calculate square-root
bfac
$x->bfac(); # factorial of $x (1*2*3*4*..$x)
round
$x->round($A,$P,$round_mode);
Round $x to accuracy $A or precision $P using the round mode
$round_mode.
bround
$x->bround($N); # accuracy: preserve $N digits
bfround
$x->bfround($N); # round to $Nth digit, no-op for BigInts
bfloor
$x->bfloor();
Set $x to the integer less or equal than $x. This is a no-op
in BigInt, but does change $x in BigFloat.
bceil
$x->bceil();
Set $x to the integer greater or equal than $x. This is a
no-op in BigInt, but does change $x in BigFloat.
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bgcd
bgcd(@values); # greatest common divisor (no OO style)
blcm
blcm(@values); # lowest common multiplicator (no OO style)
head2 length
$x->length();
($xl,$fl) = $x->length();
Returns the number of digits in the decimal representation
of the number. In list context, returns the length of the
integer and fraction part. For BigInt's, the length of the
fraction part will always be 0.
exponent
$x->exponent();
Return the exponent of $x as BigInt.
mantissa
$x->mantissa();
Return the signed mantissa of $x as BigInt.
parts
$x->parts(); # return (mantissa,exponent) as BigInt
copy
$x->copy(); # make a true copy of $x (unlike $y = $x;)
as_int
$x->as_int();
Returns $x as a BigInt (truncated towards zero). In BigInt
this is the same as "copy()".
"as_number()" is an alias to this method. "as_number" was
introduced in v1.22, while "as_int()" was only introduced in
v1.68.
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bstr
$x->bstr();
Returns a normalized string represantation of $x.
bsstr
$x->bsstr(); # normalized string in scientific notation
as_hex
$x->as_hex(); # as signed hexadecimal string with prefixed 0x
as_bin
$x->as_bin(); # as signed binary string with prefixed 0b
ACCURACY and PRECISION
Since version v1.33, Math::BigInt and Math::BigFloat have
full support for accuracy and precision based rounding, both
automatically after every operation, as well as manually.
This section describes the accuracy/precision handling in
Math::Big* as it used to be and as it is now, complete with
an explanation of all terms and abbreviations.
Not yet implemented things (but with correct description)
are marked with '!', things that need to be answered are
marked with '?'.
In the next paragraph follows a short description of terms
used here (because these may differ from terms used by oth-
ers people or documentation).
During the rest of this document, the shortcuts A (for accu-
racy), P (for precision), F (fallback) and R (rounding mode)
will be used.
Precision P
A fixed number of digits before (positive) or after (nega-
tive) the decimal point. For example, 123.45 has a precision
of -2. 0 means an integer like 123 (or 120). A precision of
2 means two digits to the left of the decimal point are
zero, so 123 with P = 1 becomes 120. Note that numbers with
zeros before the decimal point may have different preci-
sions, because 1200 can have p = 0, 1 or 2 (depending on
what the inital value was). It could also have p < 0, when
the digits after the decimal point are zero.
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The string output (of floating point numbers) will be padded
with zeros:
Initial value P A Result String
------------------------------------------------------------
1234.01 -3 1000 1000
1234 -2 1200 1200
1234.5 -1 1230 1230
1234.001 1 1234 1234.0
1234.01 0 1234 1234
1234.01 2 1234.01 1234.01
1234.01 5 1234.01 1234.01000
For BigInts, no padding occurs.
Accuracy A
Number of significant digits. Leading zeros are not counted.
A number may have an accuracy greater than the non-zero
digits when there are zeros in it or trailing zeros. For
example, 123.456 has A of 6, 10203 has 5, 123.0506 has 7,
123.450000 has 8 and 0.000123 has 3.
The string output (of floating point numbers) will be padded
with zeros:
Initial value P A Result String
------------------------------------------------------------
1234.01 3 1230 1230
1234.01 6 1234.01 1234.01
1234.1 8 1234.1 1234.1000
For BigInts, no padding occurs.
Fallback F
When both A and P are undefined, this is used as a fallback
accuracy when dividing numbers.
Rounding mode R
When rounding a number, different 'styles' or 'kinds' of
rounding are possible. (Note that random rounding, as in
Math::Round, is not implemented.)
'trunc'
truncation invariably removes all digits following the
rounding place, replacing them with zeros. Thus, 987.65
rounded to tens (P=1) becomes 980, and rounded to the
fourth sigdig becomes 987.6 (A=4). 123.456 rounded to the
second place after the decimal point (P=-2) becomes
123.46.
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All other implemented styles of rounding attempt to round
to the "nearest digit." If the digit D immediately to the
right of the rounding place (skipping the decimal point)
is greater than 5, the number is incremented at the round-
ing place (possibly causing a cascade of incrementation):
e.g. when rounding to units, 0.9 rounds to 1, and -19.9
rounds to -20. If D < 5, the number is similarly truncated
at the rounding place: e.g. when rounding to units, 0.4
rounds to 0, and -19.4 rounds to -19.
However the results of other styles of rounding differ if
the digit immediately to the right of the rounding place
(skipping the decimal point) is 5 and if there are no
digits, or no digits other than 0, after that 5. In such
cases:
'even'
rounds the digit at the rounding place to 0, 2, 4, 6, or 8
if it is not already. E.g., when rounding to the first
sigdig, 0.45 becomes 0.4, -0.55 becomes -0.6, but 0.4501
becomes 0.5.
'odd'
rounds the digit at the rounding place to 1, 3, 5, 7, or 9
if it is not already. E.g., when rounding to the first
sigdig, 0.45 becomes 0.5, -0.55 becomes -0.5, but 0.5501
becomes 0.6.
'+inf'
round to plus infinity, i.e. always round up. E.g., when
rounding to the first sigdig, 0.45 becomes 0.5, -0.55
becomes -0.5, and 0.4501 also becomes 0.5.
'-inf'
round to minus infinity, i.e. always round down. E.g.,
when rounding to the first sigdig, 0.45 becomes 0.4, -0.55
becomes -0.6, but 0.4501 becomes 0.5.
'zero'
round to zero, i.e. positive numbers down, negative ones
up. E.g., when rounding to the first sigdig, 0.45 becomes
0.4, -0.55 becomes -0.5, but 0.4501 becomes 0.5.
The handling of A & P in MBI/MBF (the old core code shipped
with Perl versions <= 5.7.2) is like this:
Precision
* ffround($p) is able to round to $p number of digits after the decimal
point
* otherwise P is unused
Accuracy (significant digits)
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* fround($a) rounds to $a significant digits
* only fdiv() and fsqrt() take A as (optional) paramater
+ other operations simply create the same number (fneg etc), or more (fmul)
of digits
+ rounding/truncating is only done when explicitly calling one of fround
or ffround, and never for BigInt (not implemented)
* fsqrt() simply hands its accuracy argument over to fdiv.
* the documentation and the comment in the code indicate two different ways
on how fdiv() determines the maximum number of digits it should calculate,
and the actual code does yet another thing
POD:
max($Math::BigFloat::div_scale,length(dividend)+length(divisor))
Comment:
result has at most max(scale, length(dividend), length(divisor)) digits
Actual code:
scale = max(scale, length(dividend)-1,length(divisor)-1);
scale += length(divisior) - length(dividend);
So for lx = 3, ly = 9, scale = 10, scale will actually be 16 (10+9-3).
Actually, the 'difference' added to the scale is calculated from the
number of "significant digits" in dividend and divisor, which is derived
by looking at the length of the mantissa. Which is wrong, since it includes
the + sign (oops) and actually gets 2 for '+100' and 4 for '+101'. Oops
again. Thus 124/3 with div_scale=1 will get you '41.3' based on the strange
assumption that 124 has 3 significant digits, while 120/7 will get you
'17', not '17.1' since 120 is thought to have 2 significant digits.
The rounding after the division then uses the remainder and $y to determine
wether it must round up or down.
? I have no idea which is the right way. That's why I used a slightly more
? simple scheme and tweaked the few failing testcases to match it.
This is how it works now:
Setting/Accessing
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* You can set the A global via C<< Math::BigInt->accuracy() >> or
C<< Math::BigFloat->accuracy() >> or whatever class you are using.
* You can also set P globally by using C<< Math::SomeClass->precision() >>
likewise.
* Globals are classwide, and not inherited by subclasses.
* to undefine A, use C<< Math::SomeCLass->accuracy(undef); >>
* to undefine P, use C<< Math::SomeClass->precision(undef); >>
* Setting C<< Math::SomeClass->accuracy() >> clears automatically
C<< Math::SomeClass->precision() >>, and vice versa.
* To be valid, A must be > 0, P can have any value.
* If P is negative, this means round to the P'th place to the right of the
decimal point; positive values mean to the left of the decimal point.
P of 0 means round to integer.
* to find out the current global A, use C<< Math::SomeClass->accuracy() >>
* to find out the current global P, use C<< Math::SomeClass->precision() >>
* use C<< $x->accuracy() >> respective C<< $x->precision() >> for the local
setting of C<< $x >>.
* Please note that C<< $x->accuracy() >> respecive C<< $x->precision() >>
return eventually defined global A or P, when C<< $x >>'s A or P is not
set.
Creating numbers
* When you create a number, you can give it's desired A or P via:
$x = Math::BigInt->new($number,$A,$P);
* Only one of A or P can be defined, otherwise the result is NaN
* If no A or P is give ($x = Math::BigInt->new($number) form), then the
globals (if set) will be used. Thus changing the global defaults later on
will not change the A or P of previously created numbers (i.e., A and P of
$x will be what was in effect when $x was created)
* If given undef for A and P, B<no> rounding will occur, and the globals will
B<not> be used. This is used by subclasses to create numbers without
suffering rounding in the parent. Thus a subclass is able to have it's own
globals enforced upon creation of a number by using
C<< $x = Math::BigInt->new($number,undef,undef) >>:
use Math::BigInt::SomeSubclass;
use Math::BigInt;
Math::BigInt->accuracy(2);
Math::BigInt::SomeSubClass->accuracy(3);
$x = Math::BigInt::SomeSubClass->new(1234);
$x is now 1230, and not 1200. A subclass might choose to implement
this otherwise, e.g. falling back to the parent's A and P.
Usage
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* If A or P are enabled/defined, they are used to round the result of each
operation according to the rules below
* Negative P is ignored in Math::BigInt, since BigInts never have digits
after the decimal point
* Math::BigFloat uses Math::BigInt internally, but setting A or P inside
Math::BigInt as globals does not tamper with the parts of a BigFloat.
A flag is used to mark all Math::BigFloat numbers as 'never round'.
Precedence
* It only makes sense that a number has only one of A or P at a time.
If you set either A or P on one object, or globally, the other one will
be automatically cleared.
* If two objects are involved in an operation, and one of them has A in
effect, and the other P, this results in an error (NaN).
* A takes precendence over P (Hint: A comes before P).
If neither of them is defined, nothing is used, i.e. the result will have
as many digits as it can (with an exception for fdiv/fsqrt) and will not
be rounded.
* There is another setting for fdiv() (and thus for fsqrt()). If neither of
A or P is defined, fdiv() will use a fallback (F) of $div_scale digits.
If either the dividend's or the divisor's mantissa has more digits than
the value of F, the higher value will be used instead of F.
This is to limit the digits (A) of the result (just consider what would
happen with unlimited A and P in the case of 1/3 :-)
* fdiv will calculate (at least) 4 more digits than required (determined by
A, P or F), and, if F is not used, round the result
(this will still fail in the case of a result like 0.12345000000001 with A
or P of 5, but this can not be helped - or can it?)
* Thus you can have the math done by on Math::Big* class in two modi:
+ never round (this is the default):
This is done by setting A and P to undef. No math operation
will round the result, with fdiv() and fsqrt() as exceptions to guard
against overflows. You must explicitely call bround(), bfround() or
round() (the latter with parameters).
Note: Once you have rounded a number, the settings will 'stick' on it
and 'infect' all other numbers engaged in math operations with it, since
local settings have the highest precedence. So, to get SaferRound[tm],
use a copy() before rounding like this:
$x = Math::BigFloat->new(12.34);
$y = Math::BigFloat->new(98.76);
$z = $x * $y; # 1218.6984
print $x->copy()->fround(3); # 12.3 (but A is now 3!)
$z = $x * $y; # still 1218.6984, without
# copy would have been 1210!
+ round after each op:
After each single operation (except for testing like is_zero()), the
method round() is called and the result is rounded appropriately. By
setting proper values for A and P, you can have all-the-same-A or
all-the-same-P modes. For example, Math::Currency might set A to undef,
and P to -2, globally.
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Math::BigInt(3p)Perl Programmers Reference Guide Math::BigInt(3p)
?Maybe an extra option that forbids local A & P settings would be in order,
?so that intermediate rounding does not 'poison' further math?
Overriding globals
* you will be able to give A, P and R as an argument to all the calculation
routines; the second parameter is A, the third one is P, and the fourth is
R (shift right by one for binary operations like badd). P is used only if
the first parameter (A) is undefined. These three parameters override the
globals in the order detailed as follows, i.e. the first defined value
wins:
(local: per object, global: global default, parameter: argument to sub)
+ parameter A
+ parameter P
+ local A (if defined on both of the operands: smaller one is taken)
+ local P (if defined on both of the operands: bigger one is taken)
+ global A
+ global P
+ global F
* fsqrt() will hand its arguments to fdiv(), as it used to, only now for two
arguments (A and P) instead of one
Local settings
* You can set A or P locally by using C<< $x->accuracy() >> or
C<< $x->precision() >>
and thus force different A and P for different objects/numbers.
* Setting A or P this way immediately rounds $x to the new value.
* C<< $x->accuracy() >> clears C<< $x->precision() >>, and vice versa.
Rounding
* the rounding routines will use the respective global or local settings.
fround()/bround() is for accuracy rounding, while ffround()/bfround()
is for precision
* the two rounding functions take as the second parameter one of the
following rounding modes (R):
'even', 'odd', '+inf', '-inf', 'zero', 'trunc'
* you can set/get the global R by using C<< Math::SomeClass->round_mode() >>
or by setting C<< $Math::SomeClass::round_mode >>
* after each operation, C<< $result->round() >> is called, and the result may
eventually be rounded (that is, if A or P were set either locally,
globally or as parameter to the operation)
* to manually round a number, call C<< $x->round($A,$P,$round_mode); >>
this will round the number by using the appropriate rounding function
and then normalize it.
* rounding modifies the local settings of the number:
$x = Math::BigFloat->new(123.456);
$x->accuracy(5);
$x->bround(4);
Here 4 takes precedence over 5, so 123.5 is the result and $x->accuracy()
will be 4 from now on.
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Default values
* R: 'even'
* F: 40
* A: undef
* P: undef
Remarks
* The defaults are set up so that the new code gives the same results as
the old code (except in a few cases on fdiv):
+ Both A and P are undefined and thus will not be used for rounding
after each operation.
+ round() is thus a no-op, unless given extra parameters A and P
Infinity and Not a Number
While BigInt has extensive handling of inf and NaN, certain
quirks remain.
oct()/hex()
These perl routines currently (as of Perl v.5.8.6) cannot
handle passed inf.
te@linux:~> perl -wle 'print 2 ** 3333'
inf
te@linux:~> perl -wle 'print 2 ** 3333 == 2 ** 3333'
1
te@linux:~> perl -wle 'print oct(2 ** 3333)'
0
te@linux:~> perl -wle 'print hex(2 ** 3333)'
Illegal hexadecimal digit 'i' ignored at -e line 1.
0
The same problems occur if you pass them
Math::BigInt->binf() objects. Since overloading these rou-
tines is not possible, this cannot be fixed from BigInt.
==, !=, <, >, <=, >= with NaNs
BigInt's bcmp() routine currently returns undef to signal
that a NaN was involved in a comparisation. However, the
overload code turns that into either 1 or '' and thus
operations like "NaN != NaN" might return wrong values.
log(-inf)
"log(-inf)" is highly weird. Since log(-x)=pi*i+log(x),
then log(-inf)=pi*i+inf. However, since the imaginary part
is finite, the real infinity "overshadows" it, so the
number might as well just be infinity. However, the result
is a complex number, and since BigInt/BigFloat can only
have real numbers as results, the result is NaN.
exp(), cos(), sin(), atan2()
These all might have problems handling infinity right.
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Math::BigInt(3p)Perl Programmers Reference Guide Math::BigInt(3p)INTERNALS
The actual numbers are stored as unsigned big integers (with
seperate sign).
You should neither care about nor depend on the internal
representation; it might change without notice. Use ONLY
method calls like "$x->sign();" instead relying on the
internal representation.
MATH LIBRARY
Math with the numbers is done (by default) by a module
called "Math::BigInt::Calc". This is equivalent to saying:
use Math::BigInt lib => 'Calc';
You can change this by using:
use Math::BigInt lib => 'BitVect';
The following would first try to find Math::BigInt::Foo,
then Math::BigInt::Bar, and when this also fails, revert to
Math::BigInt::Calc:
use Math::BigInt lib => 'Foo,Math::BigInt::Bar';
Since Math::BigInt::GMP is in almost all cases faster than
Calc (especially in math involving really big numbers, where
it is much faster), and there is no penalty if
Math::BigInt::GMP is not installed, it is a good idea to
always use the following:
use Math::BigInt lib => 'GMP';
Different low-level libraries use different formats to store
the numbers. You should NOT depend on the number having a
specific format internally.
See the respective math library module documentation for
further details.
SIGN
The sign is either '+', '-', 'NaN', '+inf' or '-inf'.
A sign of 'NaN' is used to represent the result when input
arguments are not numbers or as a result of 0/0. '+inf' and
'-inf' represent plus respectively minus infinity. You will
get '+inf' when dividing a positive number by 0, and '-inf'
when dividing any negative number by 0.
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Math::BigInt(3p)Perl Programmers Reference Guide Math::BigInt(3p)mantissa(), exponent() and parts()
"mantissa()" and "exponent()" return the said parts of the
BigInt such that:
$m = $x->mantissa();
$e = $x->exponent();
$y = $m * ( 10 ** $e );
print "ok\n" if $x == $y;
"($m,$e) = $x->parts()" is just a shortcut that gives you
both of them in one go. Both the returned mantissa and
exponent have a sign.
Currently, for BigInts $e is always 0, except for NaN, +inf
and -inf, where it is "NaN"; and for "$x == 0", where it is
1 (to be compatible with Math::BigFloat's internal represen-
tation of a zero as 0E1).
$m is currently just a copy of the original number. The
relation between $e and $m will stay always the same, though
their real values might change.
EXAMPLES
use Math::BigInt;
sub bint { Math::BigInt->new(shift); }
$x = Math::BigInt->bstr("1234") # string "1234"
$x = "$x"; # same as bstr()
$x = Math::BigInt->bneg("1234"); # BigInt "-1234"
$x = Math::BigInt->babs("-12345"); # BigInt "12345"
$x = Math::BigInt->bnorm("-0 00"); # BigInt "0"
$x = bint(1) + bint(2); # BigInt "3"
$x = bint(1) + "2"; # ditto (auto-BigIntify of "2")
$x = bint(1); # BigInt "1"
$x = $x + 5 / 2; # BigInt "3"
$x = $x ** 3; # BigInt "27"
$x *= 2; # BigInt "54"
$x = Math::BigInt->new(0); # BigInt "0"
$x--; # BigInt "-1"
$x = Math::BigInt->badd(4,5) # BigInt "9"
print $x->bsstr(); # 9e+0
Examples for rounding:
use Math::BigFloat;
use Test;
$x = Math::BigFloat->new(123.4567);
$y = Math::BigFloat->new(123.456789);
Math::BigFloat->accuracy(4); # no more A than 4
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ok ($x->copy()->fround(),123.4); # even rounding
print $x->copy()->fround(),"\n"; # 123.4
Math::BigFloat->round_mode('odd'); # round to odd
print $x->copy()->fround(),"\n"; # 123.5
Math::BigFloat->accuracy(5); # no more A than 5
Math::BigFloat->round_mode('odd'); # round to odd
print $x->copy()->fround(),"\n"; # 123.46
$y = $x->copy()->fround(4),"\n"; # A = 4: 123.4
print "$y, ",$y->accuracy(),"\n"; # 123.4, 4
Math::BigFloat->accuracy(undef); # A not important now
Math::BigFloat->precision(2); # P important
print $x->copy()->bnorm(),"\n"; # 123.46
print $x->copy()->fround(),"\n"; # 123.46
Examples for converting:
my $x = Math::BigInt->new('0b1'.'01' x 123);
print "bin: ",$x->as_bin()," hex:",$x->as_hex()," dec: ",$x,"\n";
Autocreating constants
After "use Math::BigInt ':constant'" all the integer
decimal, hexadecimal and binary constants in the given scope
are converted to "Math::BigInt". This conversion happens at
compile time.
In particular,
perl -MMath::BigInt=:constant -e 'print 2**100,"\n"'
prints the integer value of "2**100". Note that without
conversion of constants the expression 2**100 will be calcu-
lated as perl scalar.
Please note that strings and floating point constants are
not affected, so that
use Math::BigInt qw/:constant/;
$x = 1234567890123456789012345678901234567890
+ 123456789123456789;
$y = '1234567890123456789012345678901234567890'
+ '123456789123456789';
do not work. You need an explicit Math::BigInt->new() around
one of the operands. You should also quote large constants
to protect loss of precision:
use Math::BigInt;
$x = Math::BigInt->new('1234567889123456789123456789123456789');
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Without the quotes Perl would convert the large number to a
floating point constant at compile time and then hand the
result to BigInt, which results in an truncated result or a
NaN.
This also applies to integers that look like floating point
constants:
use Math::BigInt ':constant';
print ref(123e2),"\n";
print ref(123.2e2),"\n";
will print nothing but newlines. Use either bignum or
Math::BigFloat to get this to work.
PERFORMANCE
Using the form $x += $y; etc over $x = $x + $y is faster,
since a copy of $x must be made in the second case. For long
numbers, the copy can eat up to 20% of the work (in the case
of addition/subtraction, less for multiplication/division).
If $y is very small compared to $x, the form $x += $y is
MUCH faster than $x = $x + $y since making the copy of $x
takes more time then the actual addition.
With a technique called copy-on-write, the cost of copying
with overload could be minimized or even completely avoided.
A test implementation of COW did show performance gains for
overloaded math, but introduced a performance loss due to a
constant overhead for all other operatons. So Math::BigInt
does currently not COW.
The rewritten version of this module (vs. v0.01) is slower
on certain operations, like "new()", "bstr()" and "num-
ify()". The reason are that it does now more work and han-
dles much more cases. The time spent in these operations is
usually gained in the other math operations so that code on
the average should get (much) faster. If they don't, please
contact the author.
Some operations may be slower for small numbers, but are
significantly faster for big numbers. Other operations are
now constant (O(1), like "bneg()", "babs()" etc), instead of
O(N) and thus nearly always take much less time. These
optimizations were done on purpose.
If you find the Calc module to slow, try to install any of
the replacement modules and see if they help you.
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Alternative math libraries
You can use an alternative library to drive Math::BigInt
via:
use Math::BigInt lib => 'Module';
See "MATH LIBRARY" for more information.
For more benchmark results see
<http://bloodgate.com/perl/benchmarks.html>.
SUBCLASSING
Subclassing Math::BigInt
The basic design of Math::BigInt allows simple subclasses
with very little work, as long as a few simple rules are
followed:
+ The public API must remain consistent, i.e. if a sub-class
is overloading addition, the sub-class must use the same
name, in this case badd(). The reason for this is that
Math::BigInt is optimized to call the object methods
directly.
+ The private object hash keys like "$x-"{sign}> may not be
changed, but additional keys can be added, like
"$x-"{_custom}>.
+ Accessor functions are available for all existing object
hash keys and should be used instead of directly accessing
the internal hash keys. The reason for this is that
Math::BigInt itself has a pluggable interface which per-
mits it to support different storage methods.
More complex sub-classes may have to replicate more of the
logic internal of Math::BigInt if they need to change more
basic behaviors. A subclass that needs to merely change the
output only needs to overload "bstr()".
All other object methods and overloaded functions can be
directly inherited from the parent class.
At the very minimum, any subclass will need to provide it's
own "new()" and can store additional hash keys in the
object. There are also some package globals that must be
defined, e.g.:
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# Globals
$accuracy = undef;
$precision = -2; # round to 2 decimal places
$round_mode = 'even';
$div_scale = 40;
Additionally, you might want to provide the following two
globals to allow auto-upgrading and auto-downgrading to work
correctly:
$upgrade = undef;
$downgrade = undef;
This allows Math::BigInt to correctly retrieve package glo-
bals from the subclass, like $SubClass::precision. See
t/Math/BigInt/Subclass.pm or t/Math/BigFloat/SubClass.pm
completely functional subclass examples.
Don't forget to
use overload;
in your subclass to automatically inherit the overloading
from the parent. If you like, you can change part of the
overloading, look at Math::String for an example.
UPGRADING
When used like this:
use Math::BigInt upgrade => 'Foo::Bar';
certain operations will 'upgrade' their calculation and thus
the result to the class Foo::Bar. Usually this is used in
conjunction with Math::BigFloat:
use Math::BigInt upgrade => 'Math::BigFloat';
As a shortcut, you can use the module "bignum":
use bignum;
Also good for oneliners:
perl -Mbignum -le 'print 2 ** 255'
This makes it possible to mix arguments of different classes
(as in 2.5 + 2) as well es preserve accuracy (as in
sqrt(3)).
Beware: This feature is not fully implemented yet.
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Auto-upgrade
The following methods upgrade themselves unconditionally;
that is if upgrade is in effect, they will always hand up
their work:
bsqrt()div()blog()
Beware: This list is not complete.
All other methods upgrade themselves only when one (or all)
of their arguments are of the class mentioned in $upgrade
(This might change in later versions to a more sophisticated
scheme):
BUGSbroot() does not work
The broot() function in BigInt may only work for small
values. This will be fixed in a later version.
Out of Memory!
Under Perl prior to 5.6.0 having an "use Math::BigInt
':constant';" and "eval()" in your code will crash with
"Out of memory". This is probably an overload/exporter
bug. You can workaround by not having "eval()" and ':con-
stant' at the same time or upgrade your Perl to a newer
version.
Fails to load Calc on Perl prior 5.6.0
Since eval(' use ...') can not be used in conjunction with
':constant', BigInt will fall back to eval { require ... }
when loading the math lib on Perls prior to 5.6.0. This
simple replaces '::' with '/' and thus might fail on
filesystems using a different seperator.
CAVEATS
Some things might not work as you expect them. Below is
documented what is known to be troublesome:
bstr(), bsstr() and 'cmp'
Both "bstr()" and "bsstr()" as well as automated stringify
via overload now drop the leading '+'. The old code would
return '+3', the new returns '3'. This is to be consistent
with Perl and to make "cmp" (especially with overloading)
to work as you expect. It also solves problems with
"Test.pm", because it's "ok()" uses 'eq' internally.
Mark Biggar said, when asked about to drop the '+' alto-
gether, or make only "cmp" work:
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I agree (with the first alternative), don't add the '+' on positive
numbers. It's not as important anymore with the new internal
form for numbers. It made doing things like abs and neg easier,
but those have to be done differently now anyway.
So, the following examples will now work all as expected:
use Test;
BEGIN { plan tests => 1 }
use Math::BigInt;
my $x = new Math::BigInt 3*3;
my $y = new Math::BigInt 3*3;
ok ($x,3*3);
print "$x eq 9" if $x eq $y;
print "$x eq 9" if $x eq '9';
print "$x eq 9" if $x eq 3*3;
Additionally, the following still works:
print "$x == 9" if $x == $y;
print "$x == 9" if $x == 9;
print "$x == 9" if $x == 3*3;
There is now a "bsstr()" method to get the string in scien-
tific notation aka 1e+2 instead of 100. Be advised that
overloaded 'eq' always uses bstr() for comparisation, but
Perl will represent some numbers as 100 and others as
1e+308. If in doubt, convert both arguments to Math::BigInt
before comparing them as strings:
use Test;
BEGIN { plan tests => 3 }
use Math::BigInt;
$x = Math::BigInt->new('1e56'); $y = 1e56;
ok ($x,$y); # will fail
ok ($x->bsstr(),$y); # okay
$y = Math::BigInt->new($y);
ok ($x,$y); # okay
Alternatively, simple use "<=>" for comparisations, this
will get it always right. There is not yet a way to get a
number automatically represented as a string that matches
exactly the way Perl represents it.
See also the section about "Infinity and Not a Number" for
problems in comparing NaNs.
int()
"int()" will return (at least for Perl v5.7.1 and up)
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another BigInt, not a Perl scalar:
$x = Math::BigInt->new(123);
$y = int($x); # BigInt 123
$x = Math::BigFloat->new(123.45);
$y = int($x); # BigInt 123
In all Perl versions you can use "as_number()" or "as_int"
for the same effect:
$x = Math::BigFloat->new(123.45);
$y = $x->as_number(); # BigInt 123
$y = $x->as_int(); # ditto
This also works for other subclasses, like Math::String.
It is yet unlcear whether overloaded int() should return a
scalar or a BigInt.
If you want a real Perl scalar, use "numify()":
$y = $x->numify(); # 123 as scalar
This is seldom necessary, though, because this is done
automatically, like when you access an array:
$z = $array[$x]; # does work automatically
length
The following will probably not do what you expect:
$c = Math::BigInt->new(123);
print $c->length(),"\n"; # prints 30
It prints both the number of digits in the number and in
the fraction part since print calls "length()" in list con-
text. Use something like:
print scalar $c->length(),"\n"; # prints 3
bdiv
The following will probably not do what you expect:
print $c->bdiv(10000),"\n";
It prints both quotient and remainder since print calls
"bdiv()" in list context. Also, "bdiv()" will modify $c, so
be carefull. You probably want to use
print $c / 10000,"\n";
print scalar $c->bdiv(10000),"\n"; # or if you want to modify $c
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instead.
The quotient is always the greatest integer less than or
equal to the real-valued quotient of the two operands, and
the remainder (when it is nonzero) always has the same sign
as the second operand; so, for example,
1 / 4 => ( 0, 1)
1 / -4 => (-1,-3)
-3 / 4 => (-1, 1)
-3 / -4 => ( 0,-3)
-11 / 2 => (-5,1)
11 /-2 => (-5,-1)
As a consequence, the behavior of the operator % agrees
with the behavior of Perl's built-in % operator (as docu-
mented in the perlop manpage), and the equation
$x == ($x / $y) * $y + ($x % $y)
holds true for any $x and $y, which justifies calling the
two return values of bdiv() the quotient and remainder. The
only exception to this rule are when $y == 0 and $x is
negative, then the remainder will also be negative. See
below under "infinity handling" for the reasoning behing
this.
Perl's 'use integer;' changes the behaviour of % and / for
scalars, but will not change BigInt's way to do things.
This is because under 'use integer' Perl will do what the
underlying C thinks is right and this is different for each
system. If you need BigInt's behaving exactly like Perl's
'use integer', bug the author to implement it ;)
infinity handling
Here are some examples that explain the reasons why certain
results occur while handling infinity:
The following table shows the result of the division and
the remainder, so that the equation above holds true. Some
"ordinary" cases are strewn in to show more clearly the
reasoning:
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A / B = C, R so that C * B + R = A
=========================================================
5 / 8 = 0, 5 0 * 8 + 5 = 5
0 / 8 = 0, 0 0 * 8 + 0 = 0
0 / inf = 0, 0 0 * inf + 0 = 0
0 /-inf = 0, 0 0 * -inf + 0 = 0
5 / inf = 0, 5 0 * inf + 5 = 5
5 /-inf = 0, 5 0 * -inf + 5 = 5
-5/ inf = 0, -5 0 * inf + -5 = -5
-5/-inf = 0, -5 0 * -inf + -5 = -5
inf/ 5 = inf, 0 inf * 5 + 0 = inf
-inf/ 5 = -inf, 0 -inf * 5 + 0 = -inf
inf/ -5 = -inf, 0 -inf * -5 + 0 = inf
-inf/ -5 = inf, 0 inf * -5 + 0 = -inf
5/ 5 = 1, 0 1 * 5 + 0 = 5
-5/ -5 = 1, 0 1 * -5 + 0 = -5
inf/ inf = 1, 0 1 * inf + 0 = inf
-inf/-inf = 1, 0 1 * -inf + 0 = -inf
inf/-inf = -1, 0 -1 * -inf + 0 = inf
-inf/ inf = -1, 0 1 * -inf + 0 = -inf
8/ 0 = inf, 8 inf * 0 + 8 = 8
inf/ 0 = inf, inf inf * 0 + inf = inf
0/ 0 = NaN
These cases below violate the "remainder has the sign of
the second of the two arguments", since they wouldn't match
up otherwise.
A / B = C, R so that C * B + R = A
========================================================
-inf/ 0 = -inf, -inf -inf * 0 + inf = -inf
-8/ 0 = -inf, -8 -inf * 0 + 8 = -8
Modifying and =
Beware of:
$x = Math::BigFloat->new(5);
$y = $x;
It will not do what you think, e.g. making a copy of $x.
Instead it just makes a second reference to the same object
and stores it in $y. Thus anything that modifies $x (except
overloaded operators) will modify $y, and vice versa. Or in
other words, "=" is only safe if you modify your BigInts
only via overloaded math. As soon as you use a method call
it breaks:
$x->bmul(2);
print "$x, $y\n"; # prints '10, 10'
If you want a true copy of $x, use:
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$y = $x->copy();
You can also chain the calls like this, this will make
first a copy and then multiply it by 2:
$y = $x->copy()->bmul(2);
See also the documentation for overload.pm regarding "=".
bpow
"bpow()" (and the rounding functions) now modifies the
first argument and returns it, unlike the old code which
left it alone and only returned the result. This is to be
consistent with "badd()" etc. The first three will modify
$x, the last one won't:
print bpow($x,$i),"\n"; # modify $x
print $x->bpow($i),"\n"; # ditto
print $x **= $i,"\n"; # the same
print $x ** $i,"\n"; # leave $x alone
The form "$x **= $y" is faster than "$x = $x ** $y;",
though.
Overloading -$x
The following:
$x = -$x;
is slower than
$x->bneg();
since overload calls "sub($x,0,1);" instead of "neg($x)".
The first variant needs to preserve $x since it does not
know that it later will get overwritten. This makes a copy
of $x and takes O(N), but $x->bneg() is O(1).
Mixing different object types
In Perl you will get a floating point value if you do one
of the following:
$float = 5.0 + 2;
$float = 2 + 5.0;
$float = 5 / 2;
With overloaded math, only the first two variants will
result in a BigFloat:
use Math::BigInt;
use Math::BigFloat;
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$mbf = Math::BigFloat->new(5);
$mbi2 = Math::BigInteger->new(5);
$mbi = Math::BigInteger->new(2);
# what actually gets called:
$float = $mbf + $mbi; # $mbf->badd()
$float = $mbf / $mbi; # $mbf->bdiv()
$integer = $mbi + $mbf; # $mbi->badd()
$integer = $mbi2 / $mbi; # $mbi2->bdiv()
$integer = $mbi2 / $mbf; # $mbi2->bdiv()
This is because math with overloaded operators follows the
first (dominating) operand, and the operation of that is
called and returns thus the result. So,
Math::BigInt::bdiv() will always return a Math::BigInt,
regardless whether the result should be a Math::BigFloat or
the second operant is one.
To get a Math::BigFloat you either need to call the opera-
tion manually, make sure the operands are already of the
proper type or casted to that type via
Math::BigFloat->new():
$float = Math::BigFloat->new($mbi2) / $mbi; # = 2.5
Beware of simple "casting" the entire expression, this
would only convert the already computed result:
$float = Math::BigFloat->new($mbi2 / $mbi); # = 2.0 thus wrong!
Beware also of the order of more complicated expressions
like:
$integer = ($mbi2 + $mbi) / $mbf; # int / float => int
$integer = $mbi2 / Math::BigFloat->new($mbi); # ditto
If in doubt, break the expression into simpler terms, or
cast all operands to the desired resulting type.
Scalar values are a bit different, since:
$float = 2 + $mbf;
$float = $mbf + 2;
will both result in the proper type due to the way the
overloaded math works.
This section also applies to other overloaded math pack-
ages, like Math::String.
One solution to you problem might be
autoupgrading|upgrading. See the pragmas bignum, bigint and
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bigrat for an easy way to do this.
bsqrt()
"bsqrt()" works only good if the result is a big integer,
e.g. the square root of 144 is 12, but from 12 the square
root is 3, regardless of rounding mode. The reason is that
the result is always truncated to an integer.
If you want a better approximation of the square root, then
use:
$x = Math::BigFloat->new(12);
Math::BigFloat->precision(0);
Math::BigFloat->round_mode('even');
print $x->copy->bsqrt(),"\n"; # 4
Math::BigFloat->precision(2);
print $x->bsqrt(),"\n"; # 3.46
print $x->bsqrt(3),"\n"; # 3.464
brsft()
For negative numbers in base see also brsft.
LICENSE
This program is free software; you may redistribute it
and/or modify it under the same terms as Perl itself.
SEE ALSO
Math::BigFloat, Math::BigRat and Math::Big as well as
Math::BigInt::BitVect, Math::BigInt::Pari and
Math::BigInt::GMP.
The pragmas bignum, bigint and bigrat also might be of
interest because they solve the autoupgrading/downgrading
issue, at least partly.
The package at
<http://search.cpan.org/search?mode=module&query=Math%3A%3ABigInt>
contains more documentation including a full version his-
tory, testcases, empty subclass files and benchmarks.
AUTHORS
Original code by Mark Biggar, overloaded interface by Ilya
Zakharevich. Completely rewritten by Tels
http://bloodgate.com in late 2000, 2001 - 2004 and still at
it in 2005.
Many people contributed in one or more ways to the final
beast, see the file CREDITS for an (uncomplete) list. If you
miss your name, please drop me a mail. Thank you!
perl v5.8.8 2005-02-05 36
