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gawk: Checking for MPFR

 15.6 How To Check If MPFR Is Available
 Occasionally, you might like to be able to check if 'gawk' was invoked
 with the '-M' option, enabling arbitrary-precision arithmetic.  You can
 do so with the following function, contributed by Andrew Schorr:
      # adequate_math_precision --- return true if we have enough bits
      function adequate_math_precision(n)
          return (1 != (1+(1/(2^(n-1)))))
    Here is code that invokes the function in order to check if
 arbitrary-precision arithmetic is available:
      BEGIN {
          # How many bits of mantissa precision are required
          # for this program to function properly?
          fpbits = 123
          # We hope that we were invoked with MPFR enabled. If so, the
          # following statement should configure calculations to our desired
          # precision.
          PREC = fpbits
          if (! adequate_math_precision(fpbits)) {
              print("Error: insufficient computation precision available.\n" \
                    "Try again with the -M argument?") > "/dev/stderr"
              exit 1
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