Fix issues with floating point precision and rounding #163
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This was referenced Dec 18, 2025
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This commit started off because I wanted to remove MPFR as a dependency. After an initially-incorrect attempt at doing so, I discovered two more problems. First, the test suite didn't have any tests verifying that MPFR actually fixed the problem it was introduced to fix (correctly rounding results like 0.1*1000 to 100 instead of 99). Second, MPFR gets 0.1*1000, but still makes rounding mistakes in other cases--I found this out by fuzzing after my initial incorrect patch. So now I've replaced MPFR with exact rational math in libgmp, and added regression tests for the rounding errors in string parsing. To do this, I had to do the parsing manually; I followed the same regex approach that the existing function uses. Signed-off-by: Jon Oster <jon.i.oster@gmail.com>
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This commit started off because I wanted to remove MPFR as a dependency. After an initially-incorrect attempt at doing so in #161, and a nice review by @PlasmaPower, I discovered two more problems. First, the test suite didn't have any tests verifying that MPFR actually fixed the problem it was introduced to fix (correctly rounding results like 0.1*1000 to 100 instead of 99). Second, MPFR gets 0.1*1000 right, but still makes rounding mistakes in other cases--I found this out by doing some fuzzing after my initial incorrect patch.
So now I've replaced MPFR with exact rational math in libgmp, and added regression tests for the rounding errors in string parsing. To do this, I had to do the parsing manually; I followed the same regex approach that the existing bs_size_new_from_str function uses.