Common: Add convenience function for hashing a struct

This commit is contained in:
Yuri Kunde Schlesner 2018-01-15 01:05:15 -08:00
parent 7f77820460
commit d93ee65164
3 changed files with 15 additions and 5 deletions

View file

@ -20,4 +20,17 @@ static inline u64 ComputeHash64(const void* data, size_t len) {
return CityHash64(static_cast<const char*>(data), len); return CityHash64(static_cast<const char*>(data), len);
} }
/**
* Computes a 64-bit hash of a struct. In addition to being POD (trivially copyable and having
* standard layout), it is also critical that either the struct includes no padding, or that any
* padding is initialized to a known value by memsetting the struct to 0 before filling it in.
*/
template <typename T>
static inline u64 ComputeStructHash64(const T& data) {
static_assert(
std::is_trivially_copyable<T>::value && std::is_standard_layout<T>::value,
"Type passed to ComputeStructHash64 must be trivially copyable and standard layout");
return ComputeHash64(&data, sizeof(data));
}
} // namespace Common } // namespace Common

View file

@ -65,6 +65,7 @@ PicaShaderConfig PicaShaderConfig::BuildFromRegs(const Pica::Regs& regs) {
PicaShaderConfig res; PicaShaderConfig res;
auto& state = res.state; auto& state = res.state;
// Memset structure to zero padding bits, so that they will be deterministic when hashing
std::memset(&state, 0, sizeof(PicaShaderConfig::State)); std::memset(&state, 0, sizeof(PicaShaderConfig::State));
state.scissor_test_mode = regs.rasterizer.scissor_test.mode; state.scissor_test_mode = regs.rasterizer.scissor_test.mode;

View file

@ -131,10 +131,6 @@ union PicaShaderConfig {
} state; } state;
}; };
#if (__GNUC__ >= 5) || defined(__clang__) || defined(_MSC_VER)
static_assert(std::is_trivially_copyable<PicaShaderConfig::State>::value,
"PicaShaderConfig::State must be trivially copyable");
#endif
/** /**
* Generates the GLSL vertex shader program source code for the current Pica state * Generates the GLSL vertex shader program source code for the current Pica state
@ -156,7 +152,7 @@ namespace std {
template <> template <>
struct hash<GLShader::PicaShaderConfig> { struct hash<GLShader::PicaShaderConfig> {
size_t operator()(const GLShader::PicaShaderConfig& k) const { size_t operator()(const GLShader::PicaShaderConfig& k) const {
return Common::ComputeHash64(&k.state, sizeof(GLShader::PicaShaderConfig::State)); return Common::ComputeStructHash64(k.state);
} }
}; };
} // namespace std } // namespace std