From f528f24036698e2014f370f174abab286ef397b6 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Thu, 18 Jan 2024 13:03:38 +0100
Subject: codec: Changed hashing to crc32 and made the calculation constexpr

---
 modules/codec/c++/schema_hash.h | 60 +++++++++++++++++++++++++----------------
 1 file changed, 37 insertions(+), 23 deletions(-)

(limited to 'modules/codec/c++/schema_hash.h')

diff --git a/modules/codec/c++/schema_hash.h b/modules/codec/c++/schema_hash.h
index d4312c4..48e8d6c 100644
--- a/modules/codec/c++/schema_hash.h
+++ b/modules/codec/c++/schema_hash.h
@@ -2,22 +2,14 @@
 
 #include <forstio/string_literal.h>
 #include "schema.h"
+#include "crc32.h"
 
 namespace saw {
-struct schema_hash_combine {
-		static constexpr uint64_t apply(uint64_t seed, uint64_t v){
-				return seed ^( std::hash<uint64_t>{}(v) + 0x9e3779b9 + (seed<<6) + (seed >> 2));
-		}
-};
-
 template<string_literal lit>
 struct hash_literal {
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		constexpr std::string_view view = lit.view();
-		for(uint64_t i = 0; i < view.size(); ++i){
-			seed = schema_hash_combine::apply(seed, static_cast<uint64_t>(view[i]));
-		}
-		return seed;
+		return hash<algs::crc32>::update(seed, view);
 	}
 };
 
@@ -30,7 +22,7 @@ template<>
 struct schema_hash_seed<schema::SignedInteger> {
 	using Schema = schema::SignedInteger;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		return hash_literal<Schema::name>::apply(seed);
 	}
 };
@@ -39,7 +31,7 @@ template<>
 struct schema_hash_seed<schema::UnsignedInteger> {
 	using Schema = schema::UnsignedInteger;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		return hash_literal<Schema::name>::apply(seed);
 	}
 };
@@ -48,7 +40,7 @@ template<>
 struct schema_hash_seed<schema::FloatingPoint> {
 	using Schema = schema::FloatingPoint;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		return hash_literal<Schema::name>::apply(seed);
 	}
 };
@@ -57,7 +49,7 @@ template<>
 struct schema_hash_seed<schema::String> {
 	using Schema = schema::String;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		return hash_literal<Schema::name>::apply(seed);
 	}
 };
@@ -66,10 +58,21 @@ template<typename P, uint64_t N>
 struct schema_hash_seed<schema::Primitive<P,N>> {
 	using Schema = schema::Primitive<P,N>;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		seed = hash_literal<Schema::name>::apply(seed);
 		seed = schema_hash_seed<P>::apply(seed);
-		seed = schema_hash_combine::apply(seed, N);
+		uint64_t val = N;
+		std::array<uint8_t,sizeof(uint64_t)> dat{
+			static_cast<uint8_t>(val >> 0),
+			static_cast<uint8_t>(val >> 8),
+			static_cast<uint8_t>(val >> 16),
+			static_cast<uint8_t>(val >> 24),
+			static_cast<uint8_t>(val >> 32),
+			static_cast<uint8_t>(val >> 40),
+			static_cast<uint8_t>(val >> 48),
+			static_cast<uint8_t>(val >> 56)
+		};
+		seed = hash<algs::crc32>::update(seed, &dat[0], dat.size());
 		return seed;
 	}
 };
@@ -78,10 +81,21 @@ template<typename T, uint64_t N>
 struct schema_hash_seed<schema::Array<T,N>> {
 	using Schema = schema::Array<T,N>;
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		seed = hash_literal<Schema::name>::apply(seed);
 		seed = schema_hash_seed<T>::apply(seed);
-		seed = schema_hash_combine::apply(seed, N);
+		uint64_t val = N;
+		std::array<uint8_t,sizeof(uint64_t)> dat{
+			static_cast<uint8_t>(val >> 0),
+			static_cast<uint8_t>(val >> 8),
+			static_cast<uint8_t>(val >> 16),
+			static_cast<uint8_t>(val >> 24),
+			static_cast<uint8_t>(val >> 32),
+			static_cast<uint8_t>(val >> 40),
+			static_cast<uint8_t>(val >> 48),
+			static_cast<uint8_t>(val >> 56)
+		};
+		seed = hash<algs::crc32>::update(seed, &dat[0], dat.size());
 		return seed;
 	}
 };
@@ -91,7 +105,7 @@ struct schema_hash_seed<schema::Struct<schema::Member<V,K>...>> {
 	using Schema = schema::Struct<schema::Member<V,K>...>;
 
 	template<uint64_t i>
-	static constexpr uint64_t apply_ele(uint64_t seed){
+	static constexpr uint32_t apply_ele(uint32_t seed){
 		using Type = typename parameter_pack_type<i,V...>::type;
 		constexpr string_literal Lit = parameter_key_pack_type<i,K...>::literal;
 		using MemberT = typename parameter_pack_type<i,schema::Member<V,K>...>::type;
@@ -106,7 +120,7 @@ struct schema_hash_seed<schema::Struct<schema::Member<V,K>...>> {
 		return seed;
 	}
 
-	static constexpr uint64_t apply(uint64_t seed){
+	static constexpr uint32_t apply(uint32_t seed){
 		seed = hash_literal<Schema::name>::apply(seed);
 		if constexpr (sizeof...(V) > 0){
 			seed = apply_ele<0>(seed);
@@ -117,8 +131,8 @@ struct schema_hash_seed<schema::Struct<schema::Member<V,K>...>> {
 
 template<typename Schema>
 struct schema_hash {
-	static constexpr uint64_t apply() {
-		constexpr uint64_t seed = 0;
+	static constexpr uint32_t apply() {
+		constexpr uint32_t seed = 0;
 		return schema_hash_seed<Schema>::apply(seed);
 	}
 };
-- 
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