Synopsis

#include <math.h>

double log(double x);

float logf(float x);

long double logl(long double x);

Status

Partially implemented

Conformance

IEEE Std 1003.1-2017

Description

These functions shall compute the natural logarithm of their argument x, loge(x).

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 shall return the natural logarithm of x.

If x is ±0, a pole error shall occur and log(), logf(), and logl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively.

For finite values of x that are less than 0,  or if x is -Inf, a domain error shall occur, and  either a NaN (if supported), or  an implementation-defined value shall be returned.

If x is NaN, a NaN shall be returned.

If x is 1, +0 shall be returned.

If x is +Inf, x shall be returned.

Errors

These functions shall fail if:

  • Domain Error - The finite value of x is negative,  or x is -Inf. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to EDOM. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

  • Pole Error - The value of x is zero. 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 divide-by-zero floating-point exception shall be raised.

Tests

Untested

Known bugs

None

See Also

  1. Standard library functions
  2. Table of Contents