compat: mess around with fnv hash

1 files changed, 24 insertions, 5 deletions

diff --git a/compat/int-hash.cpp b/compat/int-hash.cpp
index 5c009b4e..79b5dfad 100644
--- a/compat/int-hash.cpp
+++ b/compat/int-hash.cpp
@@ -35,15 +35,34 @@ fm_UNROLL_8
 
 } // namespace
 
+#define fnvhash_64_ROUND() do { hash *= 0x01000193u; hash ^= (uint8_t)*str++; } while(false)
+
 uint64_t fnvhash_64(const void* str_, size_t size)
 {
-    const auto *str = (const char*)str_, *end = str + size;
+    const auto *str = (const char*)str_;
     uint32_t hash = 0x811c9dc5u;
-fm_UNROLL_4
-    for (; str != end; ++str)
+    size_t full = size / 8;
+    for (size_t i = 0; i < full; i++)
     {
-        hash *= 0x01000193u;
-        hash ^= (uint8_t)*str;
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+        fnvhash_64_ROUND();
+    }
+    switch (size & 7u)
+    {
+    case 7: fnvhash_64_ROUND(); [[fallthrough]];
+    case 6: fnvhash_64_ROUND(); [[fallthrough]];
+    case 5: fnvhash_64_ROUND(); [[fallthrough]];
+    case 4: fnvhash_64_ROUND(); [[fallthrough]];
+    case 3: fnvhash_64_ROUND(); [[fallthrough]];
+    case 2: fnvhash_64_ROUND(); [[fallthrough]];
+    case 1: fnvhash_64_ROUND(); [[fallthrough]];
+    case 0: break;
     }
     return hash;
 }