1 files changed, 123 insertions, 0 deletions
diff --git a/lib/hash.h b/lib/hash.h
new file mode 100644
index 0000000..92f3180
--- /dev/null
+++ b/lib/hash.h
@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2010-2017 Richard Braun.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Upstream site with license notes :
+ * http://git.sceen.net/rbraun/librbraun.git/
+ *
+ *
+ * Hash functions for integers and strings.
+ *
+ * Integer hashing follows Thomas Wang's paper about his 32/64-bits mix
+ * functions :
+ * - https://gist.github.com/badboy/6267743
+ *
+ * String hashing uses a variant of the djb2 algorithm with k=31, as in
+ * the implementation of the hashCode() method of the Java String class :
+ * - http://www.javamex.com/tutorials/collections/hash_function_technical.shtml
+ *
+ * Note that this algorithm isn't suitable to obtain usable 64-bits hashes
+ * and is expected to only serve as an array index producer.
+ *
+ * These functions all have a bits parameter that indicates the number of
+ * relevant bits the caller is interested in. When returning a hash, its
+ * value must be truncated so that it can fit in the requested bit size.
+ * It can be used by the implementation to select high or low bits, depending
+ * on their relative randomness. To get complete, unmasked hashes, use the
+ * HASH_ALLBITS macro.
+ */
+
+#ifndef _HASH_H
+#define _HASH_H
+
+#include <assert.h>
+#include <stdint.h>
+
+#ifdef __LP64__
+#define HASH_ALLBITS 64
+#define hash_long(n, bits) hash_int64(n, bits)
+#else /* __LP64__ */
+#define HASH_ALLBITS 32
+#define hash_long(n, bits) hash_int32(n, bits)
+#endif
+
+static inline uint32_t
+hash_int32(uint32_t n, unsigned int bits)
+{
+    uint32_t hash;
+
+    hash = n;
+    hash = ~hash + (hash << 15);
+    hash ^= (hash >> 12);
+    hash += (hash << 2);
+    hash ^= (hash >> 4);
+    hash += (hash << 3) + (hash << 11);
+    hash ^= (hash >> 16);
+
+    return hash >> (32 - bits);
+}
+
+static inline uint64_t
+hash_int64(uint64_t n, unsigned int bits)
+{
+    uint64_t hash;
+
+    hash = n;
+    hash = ~hash + (hash << 21);
+    hash ^= (hash >> 24);
+    hash += (hash << 3) + (hash << 8);
+    hash ^= (hash >> 14);
+    hash += (hash << 2) + (hash << 4);
+    hash ^= (hash >> 28);
+    hash += (hash << 31);
+
+    return hash >> (64 - bits);
+}
+
+static inline uintptr_t
+hash_ptr(const void *ptr, unsigned int bits)
+{
+    if (sizeof(uintptr_t) == 8) {
+        return hash_int64((uintptr_t)ptr, bits);
+    } else {
+        return hash_int32((uintptr_t)ptr, bits);
+    }
+}
+
+static inline unsigned long
+hash_str(const char *str, unsigned int bits)
+{
+    unsigned long hash;
+    char c;
+
+    for (hash = 0; /* no condition */; str++) {
+        c = *str;
+
+        if (c == '\0') {
+            break;
+        }
+
+        hash = ((hash << 5) - hash) + c;
+    }
+
+    return hash & ((1 << bits) - 1);
+}
+
+#endif /* _HASH_H */