log#

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