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AK: Format floats with precision in scientific notation where applicable
This commit is contained in:
Callum Law
Sam Atkins
parent
1474da31c7
commit
861bcbd9ad
Notes:
github-actions[bot]
2025-08-11 16:11:59 +00:00
Author: https://github.com/Calme1709
Commit: 861bcbd9ad
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5734
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/gmta
Reviewed-by: https://github.com/tcl3
2 changed files with 75 additions and 54 deletions
123
AK/Format.cpp
123
AK/Format.cpp
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@ -590,6 +590,61 @@ ErrorOr<void> FormatBuilder::put_f32_or_f64(
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return put_string(special_case_builder.string_view(), align, min_width, NumericLimits<size_t>::max(), fill);
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}
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auto const [sign, mantissa, exponent] = convert_floating_point_to_decimal_exponential_form(value);
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auto convert_to_decimal_digits_array = [](auto x, auto& digits) -> size_t {
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size_t length = 0;
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for (; x; x /= 10)
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digits[length++] = x % 10 | '0';
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for (size_t i = 0; 2 * i + 1 < length; ++i)
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swap(digits[i], digits[length - i - 1]);
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return length;
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};
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Array<u8, 20> mantissa_digits;
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auto mantissa_length = convert_to_decimal_digits_array(mantissa, mantissa_digits);
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auto const n = exponent + static_cast<i32>(mantissa_length);
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auto mantissa_text = StringView { mantissa_digits.span().slice(0, mantissa_length) };
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// NOTE: Range from ECMA262, seems like an okay default.
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if (n < -5 || n > 21) {
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StringBuilder scientific_notation_builder;
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if (sign)
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TRY(scientific_notation_builder.try_append('-'));
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else if (sign_mode == SignMode::Always)
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TRY(scientific_notation_builder.try_append('+'));
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else if (sign_mode == SignMode::Reserved)
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TRY(scientific_notation_builder.try_append(' '));
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auto const exponent_sign = n < 0 ? '-' : '+';
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Array<u8, 5> exponent_digits;
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auto const exponent_length = convert_to_decimal_digits_array(abs(n - 1), exponent_digits);
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auto const exponent_text = StringView { exponent_digits.span().slice(0, exponent_length) };
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if (precision.has_value())
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mantissa_text = mantissa_text.substring_view(0, min(*precision + 1, mantissa_text.length())).trim("0"sv, TrimMode::Right);
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if (mantissa_text.length() == 1) {
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// <mantissa>e<exponent>
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TRY(scientific_notation_builder.try_append(mantissa_text));
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TRY(scientific_notation_builder.try_append('e'));
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TRY(scientific_notation_builder.try_append(exponent_sign));
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TRY(scientific_notation_builder.try_append(exponent_text));
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} else {
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// <mantissa>.<mantissa[1..]>e<exponent>
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TRY(scientific_notation_builder.try_append(mantissa_text.substring_view(0, 1)));
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TRY(scientific_notation_builder.try_append('.'));
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TRY(scientific_notation_builder.try_append(mantissa_text.substring_view(1)));
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TRY(scientific_notation_builder.try_append('e'));
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TRY(scientific_notation_builder.try_append(exponent_sign));
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TRY(scientific_notation_builder.try_append(exponent_text));
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}
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return put_string(scientific_notation_builder.string_view(), align, min_width, NumericLimits<size_t>::max(), fill);
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}
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if (precision.has_value() || base != 10)
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return put_f64_with_precision(value, base, upper_case, zero_pad, use_separator, align, min_width, precision.value_or(6), fill, sign_mode, display_mode);
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@ -609,20 +664,6 @@ ErrorOr<void> FormatBuilder::put_f32_or_f64(
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}
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// No precision specified, so pick the best precision with roundtrip guarantees.
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auto const [sign, mantissa, exponent] = convert_floating_point_to_decimal_exponential_form(value);
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auto convert_to_decimal_digits_array = [](auto x, auto& digits) -> size_t {
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size_t length = 0;
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for (; x; x /= 10)
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digits[length++] = x % 10 | '0';
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for (size_t i = 0; 2 * i + 1 < length; ++i)
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swap(digits[i], digits[length - i - 1]);
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return length;
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};
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Array<u8, 20> mantissa_digits;
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auto mantissa_length = convert_to_decimal_digits_array(mantissa, mantissa_digits);
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StringBuilder builder;
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if (sign)
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@ -632,48 +673,22 @@ ErrorOr<void> FormatBuilder::put_f32_or_f64(
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else if (sign_mode == SignMode::Reserved)
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TRY(builder.try_append(' '));
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auto const n = exponent + static_cast<i32>(mantissa_length);
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auto const mantissa_text = StringView { mantissa_digits.span().slice(0, mantissa_length) };
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size_t integral_part_end = 0;
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// NOTE: Range from ECMA262, seems like an okay default.
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if (n >= -5 && n <= 21) {
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if (exponent >= 0) {
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TRY(builder.try_append(mantissa_text));
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TRY(builder.try_append_repeated('0', exponent));
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integral_part_end = builder.length();
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} else if (n > 0) {
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TRY(builder.try_append(mantissa_text.substring_view(0, n)));
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integral_part_end = builder.length();
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TRY(builder.try_append('.'));
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TRY(builder.try_append(mantissa_text.substring_view(n)));
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} else {
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TRY(builder.try_append("0."sv));
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TRY(builder.try_append_repeated('0', -n));
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TRY(builder.try_append(mantissa_text));
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integral_part_end = 1;
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}
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} else {
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auto const exponent_sign = n < 0 ? '-' : '+';
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Array<u8, 5> exponent_digits;
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auto const exponent_length = convert_to_decimal_digits_array(abs(n - 1), exponent_digits);
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auto const exponent_text = StringView { exponent_digits.span().slice(0, exponent_length) };
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integral_part_end = 1;
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if (mantissa_length == 1) {
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// <mantissa>e<exponent>
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TRY(builder.try_append(mantissa_text));
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TRY(builder.try_append('e'));
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TRY(builder.try_append(exponent_sign));
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TRY(builder.try_append(exponent_text));
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} else {
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// <mantissa>.<mantissa[1..]>e<exponent>
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TRY(builder.try_append(mantissa_text.substring_view(0, 1)));
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TRY(builder.try_append('.'));
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TRY(builder.try_append(mantissa_text.substring_view(1)));
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TRY(builder.try_append('e'));
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TRY(builder.try_append(exponent_sign));
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TRY(builder.try_append(exponent_text));
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}
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if (exponent >= 0) {
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TRY(builder.try_append(mantissa_text));
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TRY(builder.try_append_repeated('0', exponent));
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integral_part_end = builder.length();
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} else if (n > 0) {
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TRY(builder.try_append(mantissa_text.substring_view(0, n)));
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integral_part_end = builder.length();
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TRY(builder.try_append('.'));
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TRY(builder.try_append(mantissa_text.substring_view(n)));
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} else {
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TRY(builder.try_append("0."sv));
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TRY(builder.try_append_repeated('0', -n));
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TRY(builder.try_append(mantissa_text));
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integral_part_end = 1;
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}
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if (use_separator && integral_part_end > 3) {
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@ -267,6 +267,12 @@ TEST_CASE(floating_point_numbers)
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EXPECT_EQ(ByteString::formatted("{:'.4}", 1234.5678), "1,234.5678");
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EXPECT_EQ(ByteString::formatted("{:'.4}", -1234.5678), "-1,234.5678");
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EXPECT_EQ(ByteString::formatted("{:.5}", 1.2345678e-15), "1.23456e-15");
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EXPECT_EQ(ByteString::formatted("{:.5}", AK::NumericLimits<float>::max()), "3.40282e+38");
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EXPECT_EQ(ByteString::formatted("{:.5}", AK::NumericLimits<float>::lowest()), "-3.40282e+38");
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EXPECT_EQ(ByteString::formatted("{:.5}", 3.000001e30), "3e+30");
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EXPECT_EQ(ByteString::formatted("{:.5}", 3.1e30), "3.1e+30");
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EXPECT_EQ(ByteString::formatted("{:.30f}", 1.0), "1.000000000000000000000000000000");
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EXPECT_EQ(ByteString::formatted("{:.30f}", 1.5), "1.500000000000000000000000000000");
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EXPECT_EQ(ByteString::formatted("{:.30f}", -2.0), "-2.000000000000000000000000000000");
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