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uucore: num_format: Move common scientific formatting code to a function

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Both format_float_scientific and format_float_shortest carry the
same code, moving it to a single function will make it possible
to optimize both.
This commit is contained in:
Nicolas Boichat
2025-08-07 14:29:21 +08:00
parent 1c6be20c00
commit f5e8609163
1 changed files with 23 additions and 25 deletions
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src/uucore/src/lib/features/format/num_format.rs
+23 -25
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@@ -374,6 +374,27 @@ fn format_float_decimal(
format!("{bd:.precision$}")
}
/// Converts a `&BigDecimal` to a scientific-like `X.XX * 10^e`.
/// - The returned `String` contains the digits `XXX`, _without_ the separating
/// `.` (the caller must add that to get a valid scientific format number).
/// - `e` is an integer exponent.
fn bd_to_string_exp_with_prec(bd: &BigDecimal, precision: u64) -> (String, i64) {
// Round bd to precision digits (including the leading digit)
// We call `with_prec` twice as it will produce an extra digit if rounding overflows
// (e.g. 9995.with_prec(3) => 1000 * 10^1, but we want 100 * 10^2).
let bd_round = bd.with_prec(precision).with_prec(precision);
// Convert to the form XXX * 10^-p (XXX is precision digit long)
let (frac, p) = bd_round.as_bigint_and_exponent();
let digits = frac.to_str_radix(10);
// If we end up with scientific formatting, we would convert XXX to X.XX:
// that divides by 10^(precision-1), so add that to the exponent.
let exponent = -p + precision as i64 - 1;
(digits, exponent)
}
fn format_float_scientific(
bd: &BigDecimal,
precision: Option<usize>,
@@ -395,20 +416,8 @@ fn format_float_scientific(
};
}
// Round bd to (1 + precision) digits (including the leading digit)
// We call `with_prec` twice as it will produce an extra digit if rounding overflows
// (e.g. 9995.with_prec(3) => 1000 * 10^1, but we want 100 * 10^2).
let bd_round = bd
.with_prec(precision as u64 + 1)
.with_prec(precision as u64 + 1);
// Convert to the form XXX * 10^-e (XXX is 1+precision digit long)
let (frac, e) = bd_round.as_bigint_and_exponent();
// Scale down "XXX" to "X.XX": that divides by 10^precision, so add that to the exponent.
let digits = frac.to_str_radix(10);
let (digits, exponent) = bd_to_string_exp_with_prec(bd, precision as u64 + 1);
let (first_digit, remaining_digits) = digits.split_at(1);
let exponent = -e + precision as i64;
let dot =
if !remaining_digits.is_empty() || (precision == 0 && ForceDecimal::Yes == force_decimal) {
@@ -445,18 +454,7 @@ fn format_float_shortest(
};
}
// Round bd to precision digits (including the leading digit)
// We call `with_prec` twice as it will produce an extra digit if rounding overflows
// (e.g. 9995.with_prec(3) => 1000 * 10^1, but we want 100 * 10^2).
let bd_round = bd.with_prec(precision as u64).with_prec(precision as u64);
// Convert to the form XXX * 10^-p (XXX is precision digit long)
let (frac, e) = bd_round.as_bigint_and_exponent();
let digits = frac.to_str_radix(10);
// If we end up with scientific formatting, we would convert XXX to X.XX:
// that divides by 10^(precision-1), so add that to the exponent.
let exponent = -e + precision as i64 - 1;
let (digits, exponent) = bd_to_string_exp_with_prec(bd, precision as u64);
if exponent < -4 || exponent >= precision as i64 {
// Scientific-ish notation (with a few differences)