LOG2(3)

NAME
1.36 `log2', `log2f'-base 2 logarithm

SYNOPSIS
     #include <math.h>
     double log2(double X);
     float log2f(float X);

DESCRIPTION
The `log2' functions compute the base-2 logarithm of X. A domain error occurs if the argument is less than zero. A range error occurs if the argument is zero.
   The Newlib implementations are not full, intrinisic calculations, but rather are derivatives based on `log'. (Accuracy might be slightly off from a direct calculation.) In addition to functions, they are also implemented as macros defined in math.h:
      #define log2(x) (log (x) / _M_LOG2_E)
      #define log2f(x) (logf (x) / (float) _M_LOG2_E)
   To use the functions instead, just undefine the macros first.
   You can use the (non-ANSI) function `matherr' to specify error handling for these functions, indirectly through the respective `log' function.

RETURNS
The `log2' functions return `log base-2(X)' on success. When X is zero, the returned value is `-HUGE_VAL' and `errno' is set to `ERANGE'. When X is negative, the returned value is NaN (not a number) and `errno' is set to `EDOM'. You can control the error behavior via `matherr'.

PORTABILITY
C99, POSIX, System V Interface Definition (Issue 6).

SEE ALSO
log2 is part of the library. The full documentation for is maintained as a Texinfo manual. If info and are properly installed at your site, the command

    info

will give you access to the complete manual.