diff options
Diffstat (limited to 'object.c')
| -rw-r--r-- | object.c | 29 |
1 files changed, 28 insertions, 1 deletions
@@ -43,14 +43,32 @@ int type_from_string(const char *str) die("invalid object type \"%s\"", str); } +/* + * Return a numerical hash value between 0 and n-1 for the object with + * the specified sha1. n must be a power of 2. Please note that the + * return value is *not* consistent across computer architectures. + */ static unsigned int hash_obj(const unsigned char *sha1, unsigned int n) { unsigned int hash; + + /* + * Since the sha1 is essentially random, we just take the + * required number of bits directly from the first + * sizeof(unsigned int) bytes of sha1. First we have to copy + * the bytes into a properly aligned integer. If we cared + * about getting consistent results across architectures, we + * would have to call ntohl() here, too. + */ memcpy(&hash, sha1, sizeof(unsigned int)); - /* Assumes power-of-2 hash sizes in grow_object_hash */ return hash & (n - 1); } +/* + * Insert obj into the hash table hash, which has length size (which + * must be a power of 2). On collisions, simply overflow to the next + * empty bucket. + */ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size) { unsigned int j = hash_obj(obj->sha1, size); @@ -63,6 +81,10 @@ static void insert_obj_hash(struct object *obj, struct object **hash, unsigned i hash[j] = obj; } +/* + * Look up the record for the given sha1 in the hash map stored in + * obj_hash. Return NULL if it was not found. + */ struct object *lookup_object(const unsigned char *sha1) { unsigned int i, first; @@ -92,6 +114,11 @@ struct object *lookup_object(const unsigned char *sha1) return obj; } +/* + * Increase the size of the hash map stored in obj_hash to the next + * power of 2 (but at least 32). Copy the existing values to the new + * hash map. + */ static void grow_object_hash(void) { int i; |