Computes the exponent of x, which is the integral part of logr |x|, as a signed floating-point value, for non-zero x, where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the <float.h> header.

If x is subnormal it is treated as though it were normalized; thus for finite positive x:

1 <= x * FLT_RADIX-logb(x) < FLT_RADIX

#include <math.h>

double logb (double x);

Return Values

Upon successful completion, these functions shall return the exponent of x.

If x is +/-0, a pole error shall occur and logb() shall return -HUGE_VAL.

If x is NaN, a NaN shall be returned.

If x is +/-Inf, +Inf shall be returned.

Requirements