Added corner cases around max value/infinity

[toughengineer]

Adding corner cases for rounding to max value or infinity according to the following comment:

@toughengineer Your statement is anything greater than the maximum value (FLT_MAX in this case) overflows to infinity. That's correct, although we first have to apply rounding.

So the last few large 32-bit numbers are $2^{127} \times (2 - 3\times 2^{-23}) $, $2^{127} \times (2 - 2\times 2^{-23}) $, $2^{127} \times (2 - 2^{-23}) $. The next number in the sequence would be $2^{128} $ but it is outside the scope. We round the number strings. Up to the midpoint between $2^{127} \times (2 - 2^{-23})$ and $2^{128} $, we round down to $2^{127} \times (2 - 2^{-23})$, then we round up (virtually) to $2^{128} $, falling into infinity.

The smallest numbers that will round to infinity are

• (32 bits) $2^{127} \times (2 - 1/2 \times 2^{-23})$ or 340282356779733661637539395458142568448.0f
• (64 bits) $2^{1023} \times (2 - 1/2 \times 2^{-52})$ or 179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497792.0

Originally posted by @lemire in #328 (comment)