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`fabs', `fabsf'--absolute value (magnitude)

     #include <math.h>
     double fabs(double X);
     float fabsf(float X);
`fabs' and `fabsf' calculate the absolute value (magnitude) of the
argument X, by direct manipulation of the bit representation of X.
The calculated value is returned.  No errors are detected.
`fabs' is ANSI.  `fabsf' is an extension.