EXPM1(3P) POSIX Programmer's Manual EXPM1(3P)[top]PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAMEexpm1, expm1f, expm1l — compute exponential functionsSYNOPSIS#include <math.h> double expm1(double x); float expm1f(float x); long double expm1l(long double x);DESCRIPTIONThe functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard. These functions shall compute ex−1.0. An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.RETURN VALUEUpon successful completion, these functions return ex−1.0. If the correct value would cause overflow, a range error shall occur and expm1(), expm1f(), and expm1l() shall return the value of the macro HUGE_VAL, HUGE_VALF, and HUGE_VALL, respectively. If x is NaN, a NaN shall be returned. If x is ±0, ±0 shall be returned. If x is −Inf, −1 shall be returned. If x is +Inf, x shall be returned. If x is subnormal, a range error may occur and x should be returned. If x is not returned, expm1(), expm1f(), and expm1l() shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.ERRORSThese functions shall fail if: Range Error The result overflows. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised. These functions may fail if: Range Error The value of x is subnormal. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the underflow floating-point exception shall be raised. The following sections are informative.EXAMPLESNone.APPLICATION USAGEThe value of expm1(x) may be more accurate than exp(x)−1.0 for small values of x. The expm1() and log1p() functions are useful for financial calculations of ((1+x)n−1)/x, namely: expm1(n * log1p(x))/x when x is very small (for example, when calculating small daily inter‐ est rates). These functions also simplify writing accurate inverse hyperbolic functions. For IEEE Std 754‐1985 double, 709.8 < x implies expm1(x) has over‐ flowed. On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.RATIONALENone.FUTURE DIRECTIONSNone.SEE ALSOexp(), feclearexcept(), fetestexcept(), ilogb(), log1p() The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of Error Conditions for Mathematical Functions, <math.h>COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information TechnologyPortable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐ cal and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.ker‐ nel.org/doc/man-pages/reporting_bugs.html .--IEEE/The Open Group 2013 EXPM1(3P)

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