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Fix up comments and readme

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wheremyfoodat 2023-07-16 19:23:42 +03:00
parent 786c3e8a5c
commit 826f0ac039
2 changed files with 8 additions and 1 deletions
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8
src/core/PICA/dynapica/shader_rec_emitter_x64.cpp
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@ -945,14 +945,19 @@ void ShaderEmitter::printLog(const PICAShader& shaderUnit) {
Xbyak::Label ShaderEmitter::emitLog2Func() {
Xbyak::Label subroutine;
// This code uses the fact that log2(float) = log2(2^exponent * mantissa)
// = log2(2^exponent) + log2(mantissa) = exponent + log2(mantissa) where mantissa has a limited range of values
// https://stackoverflow.com/a/45787548
// SSE does not have a log instruction, thus we must approximate.
// We perform this approximation first performaing a range reduction into the range [1.0, 2.0).
// We perform this approximation first performing a range reduction into the range [1.0, 2.0).
// A minimax polynomial which was fit for the function log2(x) / (x - 1) is then evaluated.
// We multiply the result by (x - 1) then restore the result into the appropriate range.
// Coefficients for the minimax polynomial.
// f(x) computes approximately log2(x) / (x - 1).
// f(x) = c4 + x * (c3 + x * (c2 + x * (c1 + x * c0)).
// We align the table of coefficients to 64 bytes, so that the whole thing will fit in 1 cache line
align(64);
const void* c0 = getCurr();
dd(0x3d74552f);
@ -1055,6 +1060,7 @@ Xbyak::Label ShaderEmitter::emitExp2Func() {
// A minimax polynomial which was fit for the function exp2(x) is then evaluated.
// We then restore the result into the appropriate range.
// Similarly to log2, we align our literal pool to 64 bytes to make sure the whole thing fits in 1 cache line
align(64);
const void* input_max = getCurr();
dd(0x43010000);