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AK: Add Formatter<FixedPoint<...>> without floating point

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Rather than casting the FixedPoint to double, format the FixedPoint
directly. This avoids using floating point instruction, which in
turn enables this to be used even in the kernel.
This commit is contained in:
Tom 2021-12-27 18:23:04 -07:00 • committed by Linus Groh
parent 77b3230c80
commit f021baf255
4 changed files with 124 additions and 15 deletions
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66
AK/Format.cpp
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@ -356,6 +356,72 @@ ErrorOr<void> FormatBuilder::put_i64(
return {};
}
ErrorOr<void> FormatBuilder::put_fixed_point(
i64 integer_value,
u64 fraction_value,
u64 fraction_one,
u8 base,
bool upper_case,
bool zero_pad,
Align align,
size_t min_width,
size_t precision,
char fill,
SignMode sign_mode)
{
StringBuilder string_builder;
FormatBuilder format_builder { string_builder };
bool is_negative = integer_value < 0;
if (is_negative)
integer_value = -integer_value;
TRY(format_builder.put_u64(static_cast<u64>(integer_value), base, false, upper_case, false, Align::Right, 0, ' ', sign_mode, is_negative));
if (precision > 0) {
// FIXME: This is a terrible approximation but doing it properly would be a lot of work. If someone is up for that, a good
// place to start would be the following video from CppCon 2019:
// https://youtu.be/4P_kbF0EbZM (Stephan T. Lavavej “Floating-Point <charconv>: Making Your Code 10x Faster With C++17's Final Boss”)
#ifdef KERNEL
// We don't have pow() in kernel land
u64 scale = 10;
for (size_t i = 0; i < precision - 1; i++) // TODO: not efficient
scale *= 10;
#else
u64 scale = pow(10.0, (double)precision);
#endif
auto fraction = (scale * fraction_value) / fraction_one; // TODO: overflows
if (is_negative)
fraction = scale - fraction;
while (fraction != 0 && fraction % 10 == 0)
fraction /= 10;
size_t visible_precision = 0;
{
auto fraction_tmp = fraction;
for (; visible_precision < precision; ++visible_precision) {
if (fraction_tmp == 0)
break;
fraction_tmp /= 10;
}
}
if (zero_pad || visible_precision > 0)
TRY(string_builder.try_append('.'));
if (visible_precision > 0)
TRY(format_builder.put_u64(fraction, base, false, upper_case, true, Align::Right, visible_precision));
if (zero_pad && (precision - visible_precision) > 0)
TRY(format_builder.put_u64(0, base, false, false, true, Align::Right, precision - visible_precision));
}
TRY(put_string(string_builder.string_view(), align, min_width, NumericLimits<size_t>::max(), fill));
return {};
}
#ifndef KERNEL
ErrorOr<void> FormatBuilder::put_f64(
double value,