Manpages - log1p.3

log1p, log1pf, log1pl - logarithm of 1 plus argument

  #include <math.h>

  double log1p(double x);
  float log1pf(float x);
  long double log1pl(long double x);

Link with -lm.

Feature Test Macro Requirements for glibc (see *feature_test_macros*(7)):

  log1p():
      _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
          || _XOPEN_SOURCE >= 500
          || /* Since glibc 2.19: */ _DEFAULT_SOURCE
          || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

*log1pf*(), *log1pl*():

      _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
          || /* Since glibc 2.19: */ _DEFAULT_SOURCE
          || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

These functions return a value equivalent to

      log (1 + x)

The result is computed in a way that is accurate even if the value of x is near zero.

On success, these functions return the natural logarithm of (1 + x).

If x is a NaN, a NaN is returned.

If x is positive infinity, positive infinity is returned.

If x is -1, a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

If x is less than -1 (including negative infinity), a domain error occurs, and a NaN (not a number) is returned.

See *math_error*(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x is less than -1

errno is set to EDOM (but see BUGS). An invalid floating-point exception (FE_INVALID) is raised.

Pole error: x is -1

errno is set to ERANGE (but see BUGS). A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised.

For an explanation of the terms used in this section, see *attributes*(7).

C99, POSIX.1-2001, POSIX.1-2008.

Before version 2.22, the glibc implementation did not set errno to EDOM when a domain error occurred.

Before version 2.22, the glibc implementation did not set errno to ERANGE when a range error occurred.

*exp*(3), *expm1*(3), *log*(3)

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