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AK: Refactor FixedPoint's formatter

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The main change is the simplification of the expression
`(10^precision * fraction) / 2^precision` to `5^precision * fraction`.

Those expressions overflow or not depends on the value of `precision`
and `fraction`. For the maximum value of `fraction`, the following table
shows for which value of `precision` overflow will occur.

            Old   New
    u32      08    10
    u64      15    20
    u128     30    39

As of now `u64` type is used to calculate the result of the expression.
Meaning that before, only FixedPoints with `precision` less than 15
could be accurately rendered (for every value of fraction) in decimal.
Now, this limit gets increased to 20.

This refactor also fixes, broken decimal render for explicitly specified
precision width in format string, and broken hexadecimal render.
This commit is contained in:
ronak69 2023-08-13 15:34:00 +00:00 • committed by Andrew Kaster
parent d40807681d
commit 352480338e
4 changed files with 147 additions and 53 deletions
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5
AK/FixedPoint.h
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@ -420,12 +420,9 @@ struct Formatter<FixedPoint<precision, Underlying>> : StandardFormatter {
{
u8 base;
bool upper_case;
FormatBuilder::RealNumberDisplayMode real_number_display_mode = FormatBuilder::RealNumberDisplayMode::General;
if (m_mode == Mode::Default || m_mode == Mode::FixedPoint) {
base = 10;
upper_case = false;
if (m_mode == Mode::FixedPoint)
real_number_display_mode = FormatBuilder::RealNumberDisplayMode::FixedPoint;
} else if (m_mode == Mode::Hexfloat) {
base = 16;
upper_case = false;
@ -446,7 +443,7 @@ struct Formatter<FixedPoint<precision, Underlying>> : StandardFormatter {
i64 integer = value.ltrunc();
constexpr u64 one = static_cast<Underlying>(1) << precision;
u64 fraction_raw = value.raw() & (one - 1);
return builder.put_fixed_point(is_negative, integer, fraction_raw, one, base, upper_case, m_zero_pad, m_use_separator, m_align, m_width.value(), m_precision.value(), m_fill, m_sign_mode, real_number_display_mode);
return builder.put_fixed_point(is_negative, integer, fraction_raw, one, precision, base, upper_case, m_zero_pad, m_use_separator, m_align, m_width.value(), m_precision.value(), m_fill, m_sign_mode);
}
};