439fea92c2
Allow the initial hash value to be passed in, as the examples do. Incrementally hash in the dvp->v_id (using the official api) rather than add it. This seems to help power-of-two predictable filename trees where the filenames repeat on a power-of-two cycle and the directory trees have power-of-two components in it. The simple add then mask was causing things like 12000+ entry collision chains while most other entries have between 0 and 3 entries each. This way seems to improve things.
69 lines
1.3 KiB
C
69 lines
1.3 KiB
C
/*
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* Fowler / Noll / Vo Hash (FNV Hash)
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* http://www.isthe.com/chongo/tech/comp/fnv/
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*
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* This is an implementation of the algorithms posted above.
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* This file is placed in the public domain by Peter Wemm.
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*
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* $FreeBSD$
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*/
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typedef u_int32_t Fnv32_t;
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typedef u_int64_t Fnv64_t;
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#define FNV1_32_INIT ((Fnv32_t) 33554467UL)
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#define FNV1_64_INIT ((Fnv64_t) 0xcbf29ce484222325ULL)
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#define FNV_32_PRIME ((Fnv32_t) 0x01000193UL)
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#define FNV_64_PRIME ((Fnv64_t) 0x100000001b3ULL)
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static __inline Fnv32_t
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fnv_32_buf(const void *buf, size_t len, Fnv32_t hval)
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{
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const u_int8_t *s = (const u_int8_t *)buf;
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while (len-- != 0) {
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hval *= FNV_32_PRIME;
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hval ^= *s++;
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}
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return hval;
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}
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static __inline Fnv32_t
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fnv_32_str(const char *str, Fnv32_t hval)
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{
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const u_int8_t *s = (const u_int8_t *)str;
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Fnv32_t c;
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while ((c = *s++) != 0) {
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hval *= FNV_32_PRIME;
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hval ^= c;
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}
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return hval;
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}
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static __inline Fnv64_t
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fnv_64_buf(const void *buf, size_t len, Fnv64_t hval)
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{
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const u_int8_t *s = (const u_int8_t *)buf;
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while (len-- != 0) {
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hval *= FNV_64_PRIME;
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hval ^= *s++;
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}
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return hval;
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}
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static __inline Fnv64_t
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fnv_64_str(const char *str, Fnv64_t hval)
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{
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const u_int8_t *s = (const u_int8_t *)str;
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u_register_t c; /* 32 bit on i386, 64 bit on alpha,ia64 */
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while ((c = *s++) != 0) {
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hval *= FNV_64_PRIME;
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hval ^= c;
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}
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return hval;
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}
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