Document some functions defined in object.c
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Acked-by: Nicolas Pitre <nico@fluxnic.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Michael Haggerty committed
Feb 28, 2014 at 17:29 UTC
33bef7ea256e620c579aeff0e672b0becc79c75c
2 files changed
+35
-1
object.c
+28
-1
@@ -43,14 +43,32 @@ int type_from_string(const char *str)
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die("invalid object type \"%s\"", str);
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}
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+/*
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+ * Return a numerical hash value between 0 and n-1 for the object with
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+ * the specified sha1. n must be a power of 2. Please note that the
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+ * return value is *not* consistent across computer architectures.
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+ */
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static unsigned int hash_obj(const unsigned char *sha1, unsigned int n)
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{
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unsigned int hash;
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+
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+ /*
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+ * Since the sha1 is essentially random, we just take the
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+ * required number of bits directly from the first
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+ * sizeof(unsigned int) bytes of sha1. First we have to copy
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+ * the bytes into a properly aligned integer. If we cared
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+ * about getting consistent results across architectures, we
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+ * would have to call ntohl() here, too.
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+ */
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memcpy(&hash, sha1, sizeof(unsigned int));
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- /* Assumes power-of-2 hash sizes in grow_object_hash */
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return hash & (n - 1);
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}
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+/*
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+ * Insert obj into the hash table hash, which has length size (which
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+ * must be a power of 2). On collisions, simply overflow to the next
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+ * empty bucket.
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+ */
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static void insert_obj_hash(struct object *obj, struct object **hash, unsigned int size)
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{
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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
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hash[j] = obj;
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}
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+/*
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+ * Look up the record for the given sha1 in the hash map stored in
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+ * obj_hash. Return NULL if it was not found.
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+ */
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struct object *lookup_object(const unsigned char *sha1)
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{
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unsigned int i, first;
@@ -92,6 +114,11 @@ struct object *lookup_object(const unsigned char *sha1)
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return obj;
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}
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+/*
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+ * Increase the size of the hash map stored in obj_hash to the next
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+ * power of 2 (but at least 32). Copy the existing values to the new
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+ * hash map.
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+ */
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static void grow_object_hash(void)
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{
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int i;
object.h
+7
@@ -42,7 +42,14 @@ struct object {
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extern const char *typename(unsigned int type);
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extern int type_from_string(const char *str);
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+/*
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+ * Return the current number of buckets in the object hashmap.
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+ */
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extern unsigned int get_max_object_index(void);
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+
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+/*
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+ * Return the object from the specified bucket in the object hashmap.
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+ */
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extern struct object *get_indexed_object(unsigned int);
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/*