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Synopsis:
    #include <math.h>
    double log2( double x );

Description:
    The log2 function computes the logarithm (base 2) of x.  A domain error
    occurs if the argument is negative.  A range error occurs if the
    argument is zero.

Returns:
    The log2 function returns the logarithm (base 2) of the argument.  When
    the argument is outside the permissible range, the  matherr function is
    called.  Unless the default  matherr function is replaced, it will set
    the global variable  errno to  EDOM, and print a "DOMAIN error"
    diagnostic message using the  stderr stream.

See Also:
    exp, log, log10, pow, matherr

Example:
    #include <stdio.h>
    #include <math.h>

    void main()
      {
        printf( "%f\n", log2(.25) );
      }

    produces the following:

    -2.000000

Classification:
    WATCOM

Systems:
    All