PROLOG  NAME  SYNOPSIS  DESCRIPTION  RETURN VALUE  ERRORS  EXAMPLES  APPLICATION USAGE  RATIONALE  FUTURE DIRECTIONS  SEE ALSO  COPYRIGHT 


EXPM1(3P) POSIX Programmer's Manual EXPM1(3P)
This 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.
expm1, expm1f, expm1l — compute exponential functions
#include <math.h> double expm1(double x); float expm1f(float x); long double expm1l(long double x);
The 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.1‐2017 defers to the ISO C standard. These functions shall compute ex1.0. 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 nonzero or fetestexcept(FE_INVALID  FE_DIVBYZERO  FE_OVERFLOW  FE_UNDERFLOW) is nonzero, an error has occurred.
Upon successful completion, these functions return ex1.0. 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 implementationdefined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
These functions shall fail if: Range Error The result overflows. If the integer expression (math_errhandling & MATH_ERRNO) is nonzero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is nonzero, then the overflow floatingpoint 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 nonzero, then errno shall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is nonzero, then the underflow floatingpoint exception shall be raised. The following sections are informative.
None.
The 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)n1)/x, namely: expm1(n * log1p(x))/x when x is very small (for example, when calculating small daily interest rates). These functions also simplify writing accurate inverse hyperbolic functions. 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 nonzero.
None.
None.
exp(3p), feclearexcept(3p), fetestexcept(3p), ilogb(3p), log1p(3p) The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of Error Conditions for Mathematical Functions, math.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.12017, Standard for Information
Technology  Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
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https://www.kernel.org/doc/manpages/reporting_bugs.html .
IEEE/The Open Group 2017 EXPM1(3P)
Pages that refer to this page: math.h(0p)