Free42 possible accuracy flaw

[Thomas Okken]

0.1^2=9.999999999999999999999999999999996e-3

Estimate for exactness: take the number of significant digits, that is, the mantissa length minus the number of trailing zeroes, and multiply that by the exponent; if <= 34, use squaring?

The estimate doesn't have to be sharp: multiply the mantissa by such a power of 10 that you get the smallest possible integer, then perform the repeated-squaring algorithm, and if the result is < 10^35, fix the exponent and return it, and otherwise, let bid128_pow() do its thing.