81 lines
1.6 KiB
C
81 lines
1.6 KiB
C
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#ifndef JHASH_H_
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#define JHASH_H_
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/*
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* Jenkins One-at-a-time hash.
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* http://burtleburtle.net/bob/hash/doobs.html
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* Also used in perl, see PERL_HASH in hv.h.
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*/
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static inline
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unsigned int jhashStringAppend(const char *str, unsigned int hash)
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{
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const char *p = str;
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while (*p) {
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hash += *p++;
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hash += (hash << 10);
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hash ^= (hash >> 6);
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}
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hash += (hash << 3);
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hash ^= (hash >> 11);
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hash += (hash << 15);
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return hash;
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}
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static inline
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unsigned int jhashDataAppend(const void *data, unsigned int len,
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unsigned int hash)
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{
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const char *p = data;
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while (len--) {
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hash += *p++;
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hash += (hash << 10);
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hash ^= (hash >> 6);
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}
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hash += (hash << 3);
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hash ^= (hash >> 11);
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hash += (hash << 15);
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return hash;
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}
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static inline
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unsigned int jhashInit(void)
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{
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/* The golden ratio really is an arbitrary value.
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* Its purpose is to avoid mapping all zeros to all zeros. */
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return 0x9e3779b9;
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}
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static inline
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unsigned int jhashString(const char *str)
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{
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return jhashStringAppend(str, jhashInit());
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}
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static inline
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unsigned int jhashData(const void *data, unsigned int len)
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{
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return jhashDataAppend(data, len, jhashInit());
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}
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/*
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* The best hash table sizes are powers of 2.
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*/
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static inline
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unsigned int jhashSize(unsigned int size)
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{
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if (size < 16)
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return 8;
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/* 640K ought to be enough for anybody. */
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if (size >= (1 << 20))
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return (1 << 20);
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/* Round down to proper power of 2.
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* See Perl_hv_ksplit in hv.c. */
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while ((size & (1 + ~size)) != size)
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size &= ~(size & (1 + ~size));
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return size;
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}
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#endif
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