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EXPM1(3P)                  POSIX Programmer's Manual                 EXPM1(3P)
PROLOG
       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
       expm1, expm1f, expm1l -- compute exponential functions
SYNOPSIS
       #include <math.h>
       double expm1(double x);
       float expm1f(float x);
       long double expm1l(long double x);
DESCRIPTION
       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.1-2008
       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 VALUE
       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
       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
       None.
APPLICATION USAGE
       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 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.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       exp(), feclearexcept(), fetestexcept(), ilogb(), log1p()
       The Base Definitions volume of POSIX.1-2008, Section 4.19, Treatment of
       Error Conditions for Mathematical Functions, <math.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  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)