This is a little trick I came up with that lets us restructure our float
classification code so we can exit earlier when the float is normal,
which is the case more often than not.
First we shift left by 1 to get rid of the sign bit, and then we count
the number of leading sign bits. If the result is less than 10 (for
doubles) or 7 (for floats), the float is normal. This is because, if the
float isn't normal, the exponent is either all zeroes or all ones.
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