From f75619bd6d21760e1da416d4e27bce6468beffcd Mon Sep 17 00:00:00 2001 From: Jeff Hostetler Date: Wed, 22 Mar 2017 17:14:21 +0000 Subject: [PATCH] hashmap: allow memihash computation to be continued Add variant of memihash() to allow the hash computation to be continued. There are times when we compute the hash on a full path and then the hash on just the path to the parent directory. This can be expensive on large repositories. With this, we can hash the parent directory first. And then continue the computation to include the "/filename". Signed-off-by: Jeff Hostetler Signed-off-by: Junio C Hamano --- hashmap.c | 17 +++++++++++++++++ hashmap.h | 1 + 2 files changed, 18 insertions(+) diff --git a/hashmap.c b/hashmap.c index b10b642229..93793cb954 100644 --- a/hashmap.c +++ b/hashmap.c @@ -50,6 +50,23 @@ unsigned int memihash(const void *buf, size_t len) return hash; } +/* + * Incoporate another chunk of data into a memihash + * computation. + */ +unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len) +{ + unsigned int hash = hash_seed; + unsigned char *ucbuf = (unsigned char *) buf; + while (len--) { + unsigned int c = *ucbuf++; + if (c >= 'a' && c <= 'z') + c -= 'a' - 'A'; + hash = (hash * FNV32_PRIME) ^ c; + } + return hash; +} + #define HASHMAP_INITIAL_SIZE 64 /* grow / shrink by 2^2 */ #define HASHMAP_RESIZE_BITS 2 diff --git a/hashmap.h b/hashmap.h index ab7958ae33..45eda693bd 100644 --- a/hashmap.h +++ b/hashmap.h @@ -12,6 +12,7 @@ extern unsigned int strhash(const char *buf); extern unsigned int strihash(const char *buf); extern unsigned int memhash(const void *buf, size_t len); extern unsigned int memihash(const void *buf, size_t len); +extern unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len); static inline unsigned int sha1hash(const unsigned char *sha1) {