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`log10', `log10f'--base 10 logarithms

     #include <math.h>
     double log10(double X);
     float log10f(float X);
`log10' returns the base 10 logarithm of X.  It is implemented as
`log(X) / log(10)'.
   `log10f' is identical, save that it takes and returns `float' values.
`log10' and `log10f' return the calculated value.
   See the description of `log' for information on errors.
`log10' is ANSI C.  `log10f' is an extension.