erofs: Add xxh32 hash function

This is a copy of the upstream bsd-2 licences code
which is also used by the kernel.

Signed-off-by: Alexander Larsson <alexl@redhat.com>

libcomposefs/lcfs-writer-erofs.c

@@ -36,6 +36,121 @@
 #include <assert.h>
 #include <linux/fsverity.h>
 
+/* The xxh32 hash function is copied from xxhash with this copyright:
+ *
+ * xxHash - Extremely 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.
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License version 2 as published by the
+ * Free Software Foundation. This program is dual-licensed; you may select
+ * either version 2 of the GNU General Public License ("GPL") or BSD license
+ * ("BSD").
+ *
+ * You can contact the author at:
+ * - xxHash homepage: https://cyan4973.github.io/xxHash/
+ * - xxHash source repository: https://github.com/Cyan4973/xxHash
+ */
+
+static const uint32_t PRIME32_1 = 2654435761U;
+static const uint32_t PRIME32_2 = 2246822519U;
+static const uint32_t PRIME32_3 = 3266489917U;
+static const uint32_t PRIME32_4 = 668265263U;
+static const uint32_t PRIME32_5 = 374761393U;
+
+static inline uint32_t get_unaligned_le32(const uint8_t *p)
+{
+	return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
+}
+
+#define xxh_rotl32(x, r) ((x << r) | (x >> (32 - r)))
+
+static uint32_t xxh32_round(uint32_t seed, const uint32_t input)
+{
+	seed += input * PRIME32_2;
+	seed = xxh_rotl32(seed, 13);
+	seed *= PRIME32_1;
+	return seed;
+}
+
+static uint32_t xxh32(const void *input, const size_t len, const uint32_t seed)
+{
+	const uint8_t *p = (const uint8_t *)input;
+	const uint8_t *b_end = p + len;
+	uint32_t h32;
+
+	if (len >= 16) {
+		const uint8_t *const limit = b_end - 16;
+		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 = xxh32_round(v1, get_unaligned_le32(p));
+			p += 4;
+			v2 = xxh32_round(v2, get_unaligned_le32(p));
+			p += 4;
+			v3 = xxh32_round(v3, get_unaligned_le32(p));
+			p += 4;
+			v4 = xxh32_round(v4, get_unaligned_le32(p));
+			p += 4;
+		} 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 += (uint32_t)len;
+
+	while (p + 4 <= b_end) {
+		h32 += get_unaligned_le32(p) * PRIME32_3;
+		h32 = xxh_rotl32(h32, 17) * PRIME32_4;
+		p += 4;
+	}
+
+	while (p < b_end) {
+		h32 += (*p) * PRIME32_5;
+		h32 = xxh_rotl32(h32, 11) * PRIME32_1;
+		p++;
+	}
+
+	h32 ^= h32 >> 15;
+	h32 *= PRIME32_2;
+	h32 ^= h32 >> 13;
+	h32 *= PRIME32_3;
+	h32 ^= h32 >> 16;
+
+	return h32;
+}
+
 struct lcfs_ctx_erofs_s {
 	struct lcfs_ctx_s base;