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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-19 00:47:55 +0000 |
commit | 26a029d407be480d791972afb5975cf62c9360a6 (patch) | |
tree | f435a8308119effd964b339f76abb83a57c29483 /third_party/rust/serde_json/src/lexical/exponent.rs | |
parent | Initial commit. (diff) | |
download | firefox-26a029d407be480d791972afb5975cf62c9360a6.tar.xz firefox-26a029d407be480d791972afb5975cf62c9360a6.zip |
Adding upstream version 124.0.1.upstream/124.0.1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'third_party/rust/serde_json/src/lexical/exponent.rs')
-rw-r--r-- | third_party/rust/serde_json/src/lexical/exponent.rs | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/third_party/rust/serde_json/src/lexical/exponent.rs b/third_party/rust/serde_json/src/lexical/exponent.rs new file mode 100644 index 0000000000..6fc51977ed --- /dev/null +++ b/third_party/rust/serde_json/src/lexical/exponent.rs @@ -0,0 +1,50 @@ +// Adapted from https://github.com/Alexhuszagh/rust-lexical. + +//! Utilities to calculate exponents. + +/// Convert usize into i32 without overflow. +/// +/// This is needed to ensure when adjusting the exponent relative to +/// the mantissa we do not overflow for comically-long exponents. +#[inline] +fn into_i32(value: usize) -> i32 { + if value > i32::max_value() as usize { + i32::max_value() + } else { + value as i32 + } +} + +// EXPONENT CALCULATION + +// Calculate the scientific notation exponent without overflow. +// +// For example, 0.1 would be -1, and 10 would be 1 in base 10. +#[inline] +pub(crate) fn scientific_exponent( + exponent: i32, + integer_digits: usize, + fraction_start: usize, +) -> i32 { + if integer_digits == 0 { + let fraction_start = into_i32(fraction_start); + exponent.saturating_sub(fraction_start).saturating_sub(1) + } else { + let integer_shift = into_i32(integer_digits - 1); + exponent.saturating_add(integer_shift) + } +} + +// Calculate the mantissa exponent without overflow. +// +// Remove the number of digits that contributed to the mantissa past +// the dot, and add the number of truncated digits from the mantissa, +// to calculate the scaling factor for the mantissa from a raw exponent. +#[inline] +pub(crate) fn mantissa_exponent(exponent: i32, fraction_digits: usize, truncated: usize) -> i32 { + if fraction_digits > truncated { + exponent.saturating_sub(into_i32(fraction_digits - truncated)) + } else { + exponent.saturating_add(into_i32(truncated - fraction_digits)) + } +} |