Returns the radix-independent exponent of the argument.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <math.h>

      double logb  (double x);

      float logbf  (float x);

      long double logbl  (long double x);

1 - Argument

 x

    A nonzero, real number.

2 - Description

    The logb functions return the exponent of x, which is the
    integral part of log(2)|x|, as a signed floating-point value,
    for nonzero x.

3 - Return Values

    x                  The exponent of x.
    -HUGE_VAL          x = 0.0; errno is set to EDOM.
    +Infinity          x is +Infinity or -Infinity.
    NaN                y is NaN; errno is set to EDOM.