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+#ifndef _JHASH_H
+#define _JHASH_H
+
+/*
+ * jhash.h
+ *
+ * Example hash function.
+ *
+ * Copyright 2009-2012 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
+ * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
+ *
+ * Permission is hereby granted to use or copy this program for any
+ * purpose, provided the above notices are retained on all copies.
+ * Permission to modify the code and to distribute modified code is
+ * granted, provided the above notices are retained, and a notice that
+ * the code was modified is included with the above copyright notice.
+ */
+
+/*
+ * Hash function
+ * Source: http://burtleburtle.net/bob/c/lookup3.c
+ * Originally Public Domain
+ */
+
+#define rot(x, k) (((x) << (k)) | ((x) >> (32 - (k))))
+
+#define mix(a, b, c) \
+do { \
+ a -= c; a ^= rot(c, 4); c += b; \
+ b -= a; b ^= rot(a, 6); a += c; \
+ c -= b; c ^= rot(b, 8); b += a; \
+ a -= c; a ^= rot(c, 16); c += b; \
+ b -= a; b ^= rot(a, 19); a += c; \
+ c -= b; c ^= rot(b, 4); b += a; \
+} while (0)
+
+#define final(a, b, c) \
+{ \
+ c ^= b; c -= rot(b, 14); \
+ a ^= c; a -= rot(c, 11); \
+ b ^= a; b -= rot(a, 25); \
+ c ^= b; c -= rot(b, 16); \
+ a ^= c; a -= rot(c, 4); \
+ b ^= a; b -= rot(a, 14); \
+ c ^= b; c -= rot(b, 24); \
+}
+
+#if (BYTE_ORDER == LITTLE_ENDIAN)
+#define HASH_LITTLE_ENDIAN 1
+#else
+#define HASH_LITTLE_ENDIAN 0
+#endif
+
+/*
+ *
+ * hashlittle() -- hash a variable-length key into a 32-bit value
+ * k : the key (the unaligned variable-length array of bytes)
+ * length : the length of the key, counting by bytes
+ * initval : can be any 4-byte value
+ * Returns a 32-bit value. Every bit of the key affects every bit of
+ * the return value. Two keys differing by one or two bits will have
+ * totally different hash values.
+ *
+ * The best hash table sizes are powers of 2. There is no need to do
+ * mod a prime (mod is sooo slow!). If you need less than 32 bits,
+ * use a bitmask. For example, if you need only 10 bits, do
+ * h = (h & hashmask(10));
+ * In which case, the hash table should have hashsize(10) elements.
+ *
+ * If you are hashing n strings (uint8_t **)k, do it like this:
+ * for (i = 0, h = 0; i < n; ++i) h = hashlittle(k[i], len[i], h);
+ *
+ * By Bob Jenkins, 2006. bob_jenkins@burtleburtle.net. You may use this
+ * code any way you wish, private, educational, or commercial. It's free.
+ *
+ * Use for hash table lookup, or anything where one collision in 2^^32 is
+ * acceptable. Do NOT use for cryptographic purposes.
+ */
+static
+uint32_t hashlittle(const void *key, size_t length, uint32_t initval)
+{
+ uint32_t a, b, c; /* internal state */
+ union {
+ const void *ptr;
+ size_t i;
+ } u;
+
+ /* Set up the internal state */
+ a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
+
+ u.ptr = key;
+ if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
+ const uint32_t *k = (const uint32_t *) key; /* read 32-bit chunks */
+
+ /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
+ while (length > 12) {
+ a += k[0];
+ b += k[1];
+ c += k[2];
+ mix(a, b, c);
+ length -= 12;
+ k += 3;
+ }
+
+ /*----------------------------- handle the last (probably partial) block */
+ /*
+ * "k[2]&0xffffff" actually reads beyond the end of the string, but
+ * then masks off the part it's not allowed to read. Because the
+ * string is aligned, the masked-off tail is in the same word as the
+ * rest of the string. Every machine with memory protection I've seen
+ * does it on word boundaries, so is OK with this. But VALGRIND will
+ * still catch it and complain. The masking trick does make the hash
+ * noticably faster for short strings (like English words).
+ */
+#ifndef VALGRIND
+
+ switch (length) {
+ case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
+ case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
+ case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
+ case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
+ case 8 : b+=k[1]; a+=k[0]; break;
+ case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
+ case 6 : b+=k[1]&0xffff; a+=k[0]; break;
+ case 5 : b+=k[1]&0xff; a+=k[0]; break;
+ case 4 : a+=k[0]; break;
+ case 3 : a+=k[0]&0xffffff; break;
+ case 2 : a+=k[0]&0xffff; break;
+ case 1 : a+=k[0]&0xff; break;
+ case 0 : return c; /* zero length strings require no mixing */
+ }
+
+#else /* make valgrind happy */
+ {
+ const uint8_t *k8;
+
+ k8 = (const uint8_t *) k;
+ switch (length) {
+ case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
+ case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
+ case 10: c+=((uint32_t) k8[9])<<8; /* fall through */
+ case 9 : c+=k8[8]; /* fall through */
+ case 8 : b+=k[1]; a+=k[0]; break;
+ case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
+ case 6 : b+=((uint32_t) k8[5])<<8; /* fall through */
+ case 5 : b+=k8[4]; /* fall through */
+ case 4 : a+=k[0]; break;
+ case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
+ case 2 : a+=((uint32_t) k8[1])<<8; /* fall through */
+ case 1 : a+=k8[0]; break;
+ case 0 : return c;
+ }
+ }
+#endif /* !valgrind */
+
+ } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
+ const uint16_t *k = (const uint16_t *) key; /* read 16-bit chunks */
+ const uint8_t *k8;
+
+ /*--------------- all but last block: aligned reads and different mixing */
+ while (length > 12)
+ {
+ a += k[0] + (((uint32_t) k[1])<<16);
+ b += k[2] + (((uint32_t) k[3])<<16);
+ c += k[4] + (((uint32_t) k[5])<<16);
+ mix(a, b, c);
+ length -= 12;
+ k += 6;
+ }
+
+ /*----------------------------- handle the last (probably partial) block */
+ k8 = (const uint8_t *) k;
+ switch(length)
+ {
+ case 12: c+=k[4]+(((uint32_t) k[5])<<16);
+ b+=k[2]+(((uint32_t) k[3])<<16);
+ a+=k[0]+(((uint32_t) k[1])<<16);
+ break;
+ case 11: c+=((uint32_t) k8[10])<<16; /* fall through */
+ case 10: c+=k[4];
+ b+=k[2]+(((uint32_t) k[3])<<16);
+ a+=k[0]+(((uint32_t) k[1])<<16);
+ break;
+ case 9 : c+=k8[8]; /* fall through */
+ case 8 : b+=k[2]+(((uint32_t) k[3])<<16);
+ a+=k[0]+(((uint32_t) k[1])<<16);
+ break;
+ case 7 : b+=((uint32_t) k8[6])<<16; /* fall through */
+ case 6 : b+=k[2];
+ a+=k[0]+(((uint32_t) k[1])<<16);
+ break;
+ case 5 : b+=k8[4]; /* fall through */
+ case 4 : a+=k[0]+(((uint32_t) k[1])<<16);
+ break;
+ case 3 : a+=((uint32_t) k8[2])<<16; /* fall through */
+ case 2 : a+=k[0];
+ break;
+ case 1 : a+=k8[0];
+ break;
+ case 0 : return c; /* zero length requires no mixing */
+ }
+
+ } else { /* need to read the key one byte at a time */
+ const uint8_t *k = (const uint8_t *)key;
+
+ /*--------------- all but the last block: affect some 32 bits of (a, b, c) */
+ while (length > 12) {
+ a += k[0];
+ a += ((uint32_t) k[1])<<8;
+ a += ((uint32_t) k[2])<<16;
+ a += ((uint32_t) k[3])<<24;
+ b += k[4];
+ b += ((uint32_t) k[5])<<8;
+ b += ((uint32_t) k[6])<<16;
+ b += ((uint32_t) k[7])<<24;
+ c += k[8];
+ c += ((uint32_t) k[9])<<8;
+ c += ((uint32_t) k[10])<<16;
+ c += ((uint32_t) k[11])<<24;
+ mix(a,b,c);
+ length -= 12;
+ k += 12;
+ }
+
+ /*-------------------------------- last block: affect all 32 bits of (c) */
+ switch (length) { /* all the case statements fall through */
+ case 12: c+=((uint32_t) k[11])<<24;
+ case 11: c+=((uint32_t) k[10])<<16;
+ case 10: c+=((uint32_t) k[9])<<8;
+ case 9 : c+=k[8];
+ case 8 : b+=((uint32_t) k[7])<<24;
+ case 7 : b+=((uint32_t) k[6])<<16;
+ case 6 : b+=((uint32_t) k[5])<<8;
+ case 5 : b+=k[4];
+ case 4 : a+=((uint32_t) k[3])<<24;
+ case 3 : a+=((uint32_t) k[2])<<16;
+ case 2 : a+=((uint32_t) k[1])<<8;
+ case 1 : a+=k[0];
+ break;
+ case 0 : return c;
+ }
+ }
+
+ final(a, b, c);
+ return c;
+}
+
+static inline
+uint32_t jhash(const void *key, size_t length, uint32_t seed)
+{
+ return hashlittle(key, length, seed);
+}
+
+#endif /* _JHASH_H */
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