From ecb7b77326b0d72e0d468316531e4d6a3f348ec4 Mon Sep 17 00:00:00 2001
From: Exzap <13877693+Exzap@users.noreply.github.com>
Date: Sat, 15 Apr 2023 10:02:56 +0200
Subject: [PATCH] Latte: Use better hashing algorithm for cache invalidation

Decreases chance of hash collisions while also being faster due to 4 channel vectorization
---
 src/Cafe/HW/Latte/Core/LatteBufferCache.cpp | 38 ++++++++++++++-------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/src/Cafe/HW/Latte/Core/LatteBufferCache.cpp b/src/Cafe/HW/Latte/Core/LatteBufferCache.cpp
index 7c484bcb..b5c1d901 100644
--- a/src/Cafe/HW/Latte/Core/LatteBufferCache.cpp
+++ b/src/Cafe/HW/Latte/Core/LatteBufferCache.cpp
@@ -734,20 +734,34 @@ private:
 
 	static uint64 hashPage(uint8* mem)
 	{
-		// note - this algorithm is/was also baked into pageWriteStreamoutSignatures()
-		uint64 h = 0;
-		uint64* memU64 = (uint64*)mem;
-		for (uint32 i = 0; i < CACHE_PAGE_SIZE / 8; i++)
-		{
-			//h = _rotr64(h, 7);
-			//h ^= *memU64;
-			//memU64++;
+		static const uint64 k0 = 0x55F23EAD;
+		static const uint64 k1 = 0x185FDC6D;
+		static const uint64 k2 = 0xF7431F49;
+		static const uint64 k3 = 0xA4C7AE9D;
 
-			h = std::rotr<uint64>(h, 7);
-			h += (*memU64 + (uint64)i);
-			memU64++;
+		cemu_assert_debug((CACHE_PAGE_SIZE % 32) == 0);
+		const uint64* ptr = (const uint64*)mem;
+		const uint64* end = ptr + (CACHE_PAGE_SIZE / sizeof(uint64));
+
+		uint64 h0 = 0;
+		uint64 h1 = 0;
+		uint64 h2 = 0;
+		uint64 h3 = 0;
+		while (ptr < end)
+		{
+			h0 = std::rotr(h0, 7);
+			h1 = std::rotr(h1, 7);
+			h2 = std::rotr(h2, 7);
+			h3 = std::rotr(h3, 7);
+
+			h0 += ptr[0] * k0;
+			h1 += ptr[1] * k1;
+			h2 += ptr[2] * k2;
+			h3 += ptr[3] * k3;
+			ptr += 4;
 		}
-		return h;
+
+		return h0 + h1 + h2 + h3;
 	}
 
 	// flag page as having streamout data, also write streamout signatures to page memory