expm1(3p) — Linux manual page

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

EXPM1(3P)               POSIX Programmer's Manual               EXPM1(3P)

PROLOG         top

       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.

NAME         top

       expm1, expm1f, expm1l — compute exponential functions

SYNOPSIS         top

       #include <math.h>

       double expm1(double x);
       float expm1f(float x);
       long double expm1l(long double x);

DESCRIPTION         top

       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 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 VALUE         top

       Upon 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.

ERRORS         top

       These 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.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       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)n-1)/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 non-zero.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       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)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, 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
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                2017                         EXPM1(3P)

Pages that refer to this page: math.h(0p)