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`log1p', `log1pf'--log of `1 + X'

     #include <math.h>
     double log1p(double X);
     float log1pf(float X);
`log1p' calculates the natural logarithm of `1+X'.  You can use `log1p'
rather than ``log(1+X)'' for greater precision when X is very small.
   `log1pf' calculates the same thing, but accepts and returns `float'
values rather than `double'.
`log1p' returns a `double', the natural log of `1+X'.  `log1pf' returns
a `float', the natural log of `1+X'.
Neither `log1p' nor `log1pf' is required by ANSI C or by the System V
Interface Definition (Issue 2).