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LibWeb: Add propper rounding to PixelUnits::operator*

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Also moves related constants into the class to make them accessible for
tests.
This commit is contained in:
Hendiadyoin1 2023-07-26 15:02:03 +02:00 • committed by Alexander Kalenik
parent 4896ba11dc
commit f9fc0505fb
3 changed files with 36 additions and 6 deletions
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26
Userland/Libraries/LibWeb/PixelUnits.cpp
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@ -9,9 +9,6 @@
namespace Web {
static i32 const fractional_bits = 6;
static constexpr i32 fixed_point_denominator = 1 << fractional_bits;
CSSPixels::CSSPixels(int value)
{
m_value = value * fixed_point_denominator;
@ -103,9 +100,26 @@ CSSPixels CSSPixels::operator-(CSSPixels const& other) const
CSSPixels CSSPixels::operator*(CSSPixels const& other) const
{
CSSPixels result;
result.set_raw_value((static_cast<i64>(raw_value()) * other.raw_value()) >> fractional_bits);
return result;
i64 value = raw_value();
value *= other.raw_value();
int int_value = AK::clamp_to_int(value >> fractional_bits);
// Rounding:
// If last bit cut off was 1:
if (value & (1u << (fractional_bits - 1))) {
// If the bit after was 1 as well
if (value & (radix_mask >> 2u)) {
// We need to round away from 0
int_value = Checked<int>::saturating_add(int_value, 1);
} else {
// Otherwise we round to the next even value
// Which means we add the least significant bit of the raw integer value
int_value = Checked<int>::saturating_add(int_value, int_value & 1);
}
}
return from_raw(int_value);
}
CSSPixels CSSPixels::operator/(CSSPixels const& other) const