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`modf', `modff'--split fractional and integer parts

     #include <math.h>
     double modf(double VAL, double *IPART);
     float modff(float VAL, float *IPART);
`modf' splits the double VAL apart into an integer part and a
fractional part, returning the fractional part and storing the integer
part in `*IPART'.  No rounding whatsoever is done; the sum of the
integer and fractional parts is guaranteed to be exactly  equal to VAL.
 That is, if . REALPART = modf(VAL, &INTPART); then
``REALPART+INTPART'' is the same as VAL.  `modff' is identical, save
that it takes and returns `float' rather than `double' values.
The fractional part is returned.  Each result has the same sign as the
supplied argument VAL.
`modf' is ANSI C. `modff' is an extension.