float: Fix panic at max exponential precision#154052
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cdown wants to merge 1 commit intorust-lang:mainfrom
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float: Fix panic at max exponential precision#154052cdown wants to merge 1 commit intorust-lang:mainfrom
cdown wants to merge 1 commit intorust-lang:mainfrom
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Rust's formatting machinery allows precision values of up to u16::MAX. Exponential formatting works out the number of significant digits to use by adding one for the digit before the decimal point (for the single digit before the decimal point). This previously used usize precision, so the maximum validated precision did not overflow, but in commit fb9ce02 ("Limit formatting width and precision to 16 bits.") the precision type was narrowed to u16 without widening that addition first. As a result an exponential precision value of 65535 is no longer handled correctly, because the digit count wraps to 0, and thus "{:.65535e}" panics in flt2dec::to_exact_exp_str with "assertion failed: ndigits > 0". Other formats (and the parser) accept values up to u16::MAX, so the deviance seems unintentional. Widen the internal exponential digit count to usize and convert before adding the additional digit.
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Rust's formatting machinery allows precision values of up to u16::MAX. Exponential formatting works out the number of significant digits to use by adding one for the digit before the decimal point (for the single digit before the decimal point).
This previously used usize precision, so the maximum validated precision did not overflow, but in commit fb9ce02 ("Limit formatting width and precision to 16 bits.") the precision type was narrowed to u16 without widening that addition first.
As a result an exponential precision value of 65535 is no longer handled correctly, because the digit count wraps to 0, and thus "{:.65535e}" panics in flt2dec::to_exact_exp_str with "assertion failed: ndigits > 0". Other formats (and the parser) accept values up to u16::MAX, so the deviance seems unintentional.
Widen the internal exponential digit count to usize and convert before adding the additional digit.