[Qemu-devel] [PATCH 06/10] include: add xxhash.h

["Emilio G. Cota" <cota@braap.org>]

xxhash is a fast, high-quality hashing function. The appended
brings in the 32-bit version of it, with the small modification that
it assumes the data to be hashed is made of 32-bit chunks; this increases
speed slightly for the use-case we care about, i.e. tb-hash.

The original algorithm, as well as a 64-bit implementation, can be found at:
  https://github.com/Cyan4973/xxHash

Signed-off-by: Emilio G. Cota <cota@braap.org>
---
 include/qemu/xxhash.h | 106 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 106 insertions(+)
 create mode 100644 include/qemu/xxhash.h

diff --git a/include/qemu/xxhash.h b/include/qemu/xxhash.h
new file mode 100644
index 0000000..a13a665
--- /dev/null
+++ b/include/qemu/xxhash.h
@@ -0,0 +1,106 @@
+/*
+ * xxHash - Fast Hash algorithm
+ * Copyright (C) 2012-2016, Yann Collet
+ *
+ * BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * + Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * + Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * You can contact the author at :
+ * - xxHash source repository : https://github.com/Cyan4973/xxHash
+ */
+#ifndef QEMU_XXHASH_H
+#define QEMU_XXHASH_H
+
+#define PRIME32_1   2654435761U
+#define PRIME32_2   2246822519U
+#define PRIME32_3   3266489917U
+#define PRIME32_4    668265263U
+#define PRIME32_5    374761393U
+
+/*
+ * Note : although _rotl exists for minGW (GCC under windows), performance
+ * seems poor.
+ */
+#if defined(_MSC_VER)
+#  define XXH_rotl32(x, r) _rotl(x, r)
+#else
+#  define XXH_rotl32(x, r) ((x << r) | (x >> (32 - r)))
+#endif
+
+/* u32 hash of @n contiguous chunks of u32's */
+static inline uint32_t qemu_xxh32(const uint32_t *p, size_t n, uint32_t seed)
+{
+    const uint32_t *end = p + n;
+    uint32_t h32;
+
+    if (n >= 4) {
+        const uint32_t * const limit = end - 4;
+        uint32_t v1 = seed + PRIME32_1 + PRIME32_2;
+        uint32_t v2 = seed + PRIME32_2;
+        uint32_t v3 = seed + 0;
+        uint32_t v4 = seed - PRIME32_1;
+
+        do {
+            v1 += *p * PRIME32_2;
+            v1 = XXH_rotl32(v1, 13);
+            v1 *= PRIME32_1;
+            p++;
+            v2 += *p * PRIME32_2;
+            v2 = XXH_rotl32(v2, 13);
+            v2 *= PRIME32_1;
+            p++;
+            v3 += *p * PRIME32_2;
+            v3 = XXH_rotl32(v3, 13);
+            v3 *= PRIME32_1;
+            p++;
+            v4 += *p * PRIME32_2;
+            v4 = XXH_rotl32(v4, 13);
+            v4 *= PRIME32_1;
+            p++;
+        } while (p <= limit);
+        h32 = XXH_rotl32(v1, 1) + XXH_rotl32(v2, 7) + XXH_rotl32(v3, 12) +
+            XXH_rotl32(v4, 18);
+    } else {
+        h32  = seed + PRIME32_5;
+    }
+
+    h32 += n * sizeof(uint32_t);
+
+    while (p < end) {
+        h32 += *p * PRIME32_3;
+        h32  = XXH_rotl32(h32, 17) * PRIME32_4 ;
+        p++;
+    }
+
+    h32 ^= h32 >> 15;
+    h32 *= PRIME32_2;
+    h32 ^= h32 >> 13;
+    h32 *= PRIME32_3;
+    h32 ^= h32 >> 16;
+
+    return h32;
+}
+
+#endif /* QEMU_XXHASH_H */
-- 
2.5.0