From c077f0f904cce505e15543b855b4330ca547b53d Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Thu, 14 Sep 2023 09:02:23 +0200
Subject: replace hash with fnv1

---
 compat/int-hash.cpp | 36 ++++++++++++++++--------------------
 1 file changed, 16 insertions(+), 20 deletions(-)

(limited to 'compat')

diff --git a/compat/int-hash.cpp b/compat/int-hash.cpp
index 00f2e474..72c38179 100644
--- a/compat/int-hash.cpp
+++ b/compat/int-hash.cpp
@@ -3,35 +3,31 @@
 
 namespace floormat {
 
-size_t int_hash(uint32_t x) noexcept
+template<typename T, T offset_basis, T prime>
+static CORRADE_ALWAYS_INLINE
+T FNVHash(const char* str, size_t size)
 {
-    if constexpr(sizeof(size_t) == 4)
+    const auto* end = str + size;
+    T hash = offset_basis;
+    for (; str != end; ++str)
     {
-        // by Chris Wellons <https://nullprogram.com/blog/2018/07/31/>
-
-        x ^= x >> 15;
-        x *= 0x2c1b3c6dU;
-        x ^= x >> 12;
-        x *= 0x297a2d39U;
-        x ^= x >> 15;
-
-        return x;
+        hash *= prime;
+        hash ^= (uint8_t)*str;
     }
+    return hash;
+}
+
+size_t int_hash(uint32_t x) noexcept
+{
+    if constexpr(sizeof(size_t) == 4)
+        return FNVHash<uint32_t, 0x811c9dc5u, 0x01000193u>((const char*)&x, 4);
     else
         return int_hash(uint64_t(x));
 }
 
 size_t int_hash(uint64_t x) noexcept
 {
-    // NASAM by Pelle Evensen <https://mostlymangling.blogspot.com/2020/01/nasam-not-another-strange-acronym-mixer.html>
-
-    x ^= std::rotr(x, 25) ^ std::rotr(x, 47);
-    x *= 0x9E6C63D0676A9A99UL;
-    x ^= x >> 23 ^ x >> 51;
-    x *= 0x9E6D62D06F6A9A9BUL;
-    x ^= x >> 23 ^ x >> 51;
-
-    return x;
+    return FNVHash<uint64_t, 0xcbf29ce484222325u, 0x100000001b3u>((const char*)&x, 8);
 }
 
 } // namespace floormat
-- 
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