From fdf5ef27fec1368a33801a98bbc5ed3556476979 Mon Sep 17 00:00:00 2001
From: Douglas Rumbaugh <dbr4@psu.edu>
Date: Mon, 8 May 2023 12:59:46 -0400
Subject: Began porting source files over from other repository

---
 include/util/hash.h | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 include/util/hash.h

(limited to 'include/util/hash.h')

diff --git a/include/util/hash.h b/include/util/hash.h
new file mode 100644
index 0000000..04871dc
--- /dev/null
+++ b/include/util/hash.h
@@ -0,0 +1,61 @@
+/*
+ * include/util/hash.h
+ *
+ * Copyright (C) 2023 Dong Xie <dongx@psu.edu>
+ *
+ * All rights reserved. Published under the Modified BSD License.
+ *
+ */
+#pragma once
+
+#include <cstdlib>
+#include <cstdint>
+
+namespace de {
+
+// 40343 is a "magic constant" that works well,
+// 38299 is another good value.
+// Both are primes and have a good distribution of bits.
+const uint64_t kHashMagicNum = 40343;
+
+inline uint64_t rotr64(uint64_t x, size_t n) {
+    return (((x) >> n) | ((x) << (64 - n)));
+}
+
+inline uint64_t hash(uint64_t input) {
+    uint64_t local_rand = input;
+    uint64_t local_rand_hash = 8;
+    local_rand_hash = 40343 * local_rand_hash + ((local_rand) & 0xFFFF);
+    local_rand_hash = 40343 * local_rand_hash + ((local_rand >> 16) & 0xFFFF);
+    local_rand_hash = 40343 * local_rand_hash + ((local_rand >> 32) & 0xFFFF);
+    local_rand_hash = 40343 * local_rand_hash + (local_rand >> 48);
+    local_rand_hash = 40343 * local_rand_hash;
+    return rotr64(local_rand_hash, 43);
+}
+
+inline uint64_t hash_bytes(const char* str, size_t len) {
+    uint64_t hashState = len;
+
+    for(size_t idx = 0; idx < len; ++idx) {
+      hashState = kHashMagicNum * hashState + str[idx];
+    }
+
+    // The final scrambling helps with short keys that vary only on the high order bits.
+    // Low order bits are not always well distributed so shift them to the high end, where they'll
+    // form part of the 14-bit tag.
+    return rotr64(kHashMagicNum * hashState, 6);
+}
+
+inline uint64_t hash_bytes_with_salt(const char* str, size_t len, uint16_t salt) {
+    uint64_t hashState = len;
+
+    for(size_t idx = 0; idx < len; ++idx) {
+      hashState = kHashMagicNum * hashState + str[idx];
+    }
+
+    hashState = kHashMagicNum * hashState + salt;
+
+    return rotr64(kHashMagicNum * hashState, 6);
+}
+
+}
-- 
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