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[Shader JIT] Use rotl+xor for combining hashes

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Co-Authored-By: Wunk <wunkolo@gmail.com>
This commit is contained in:
wheremyfoodat 2023-06-15 01:58:00 +03:00
parent b34d009520
commit 3cf4bdd95f
1 changed files with 5 additions and 4 deletions
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9
src/core/PICA/dynapica/shader_rec.cpp
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@ -1,5 +1,5 @@
#include "PICA/dynapica/shader_rec.hpp"
#include "cityhash.hpp"
#include <bit>
#ifdef PANDA3DS_SHADER_JIT_SUPPORTED
void ShaderJIT::reset() {
@ -8,10 +8,11 @@ void ShaderJIT::reset() {
void ShaderJIT::prepare(PICAShader& shaderUnit) {
shaderUnit.pc = shaderUnit.entrypoint;
// We construct a shader hash from both the code and operand descriptor hashes
// We combine the code and operand descriptor hashes into a single hash
// This is so that if only one of them changes, we still properly recompile the shader
// This code is inspired from how Citra solves this problem
Hash hash = shaderUnit.getCodeHash() ^ shaderUnit.getOpdescHash();
// The combine does rotl(x, 1) ^ y for the merging instead of x ^ y because xor is commutative, hence creating possible collisions
// re: https://github.com/wheremyfoodat/Panda3DS/pull/15#discussion_r1229925372
Hash hash = std::rotl(shaderUnit.getCodeHash(), 1) ^ shaderUnit.getOpdescHash();
auto it = cache.find(hash);
if (it == cache.end()) { // Block has not been compiled yet