pub(crate) fn parse_long_mantissa<F: RawFloat>(s: &[u8]) -> BiasedFpdec2flt)Expand description
Parse the significant digits and biased, binary exponent of a float.
This is a fallback algorithm that uses a big-integer representation of the float, and therefore is considerably slower than faster approximations. However, it will always determine how to round the significant digits to the nearest machine float, allowing use to handle near half-way cases.
Near half-way cases are halfway between two consecutive machine floats.
For example, the float 16777217.0 has a bitwise representation of
100000000000000000000000 1. Rounding to a single-precision float,
the trailing 1 is truncated. Using round-nearest, tie-even, any
value above 16777217.0 must be rounded up to 16777218.0, while
any value before or equal to 16777217.0 must be rounded down
to 16777216.0. These near-halfway conversions therefore may require
a large number of digits to unambiguously determine how to round.
The algorithms described here are based on “Processing Long Numbers Quickly”, available here: https://arxiv.org/pdf/2101.11408.pdf#section.11.