##### Synopsis

    #include <math.h>
    float logf(float x);

##### Description

logf computes the base-e logarithm of x.

##### Fast math library behavior

If x = 0, errno is set to ERANGE and logf returns -HUGE_VALF.
If x < 0, errno is set to EDOM and logf returns -HUGE_VALF.

##### IEC 60559 math library behavior

If x < 0 or x = -∞, logf returns NaN with signal.
If x = 0, logf returns -∞ with signal.
If x = ∞, logf returns ∞.
If x = NaN, logf returns x with no signal.

##### Portability

logf conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).