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Merge pull request #109887 from aaronfranke/range-rescale

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Rescale values to better utilize R128 range before snapping
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Thaddeus Crews 2025-08-26 19:01:13 -05:00
commit b267c2fc6c
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1 changed files with 32 additions and 15 deletions
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47
scene/gui/range.cpp
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@ -33,22 +33,39 @@
#include "thirdparty/misc/r128.h" #include "thirdparty/misc/r128.h"
double Range::_snapped_r128(double p_value, double p_step) { double Range::_snapped_r128(double p_value, double p_step) {
if (p_step != 0) { if (p_step == 0.0) {
// All these lines are the equivalent of: p_value = Math::floor(p_value / p_step + 0.5) * p_step; return p_value;
// Convert to String to force rounding to a decimal value (not a binary one).
String step_str = String::num(p_step);
String value_str = String::num(p_value);
R128 step_r128;
R128 value_r128;
const R128 half_r128 = R128(0.5);
r128FromString(&step_r128, step_str.ascii().get_data(), nullptr);
r128FromString(&value_r128, value_str.ascii().get_data(), nullptr);
r128Div(&value_r128, &value_r128, &step_r128);
r128Add(&value_r128, &value_r128, &half_r128);
r128Floor(&value_r128, &value_r128);
r128Mul(&value_r128, &value_r128, &step_r128);
p_value = value_r128;
} }
if (p_value > (1e18 * p_step) || p_value < -(1e18 * p_step)) {
// If the value goes outside of the range R128 supports, fallback to normal snapping.
return Math::snapped(p_value, p_step);
}
// Rescale values to better utilize R128's range before snapping.
// R128 is fixed-precision with 64 bits after the decimal point, but double already uses 53 of those,
// so a step size finer than 2^-11 will lose precision, and in practice even 1e-3 can be problematic.
// By rescaling the value and step, we can shift precision into the higher bits (effectively turning R128 into a makeshift float).
const int decimals = 14 - Math::floor(std::log10(MAX(Math::abs(p_value), p_step)));
const double scale = Math::pow(10.0, decimals);
p_value *= scale;
p_step *= scale;
// All these lines are the equivalent of: p_value = Math::floor(p_value / p_step + 0.5) * p_step;
// Convert to String to force rounding to a decimal value (not a binary one).
String step_str = String::num(p_step);
String value_str = String::num(p_value);
R128 step_r128;
R128 value_r128;
const R128 half_r128 = R128(0.5);
r128FromString(&step_r128, step_str.ascii().get_data(), nullptr);
r128FromString(&value_r128, value_str.ascii().get_data(), nullptr);
r128Div(&value_r128, &value_r128, &step_r128);
r128Add(&value_r128, &value_r128, &half_r128);
r128Floor(&value_r128, &value_r128);
r128Mul(&value_r128, &value_r128, &step_r128);
if (scale != 1.0) {
const R128 scale_r128 = R128(scale);
r128Div(&value_r128, &value_r128, &scale_r128);
}
p_value = (double)value_r128;
return p_value; return p_value;
} }