Copying the first bytes of a SHA1 is duplicated in six places, however,
the implications (wrong byte order on little-endian systems) is documented
only once.
Add a properly documented API for this.
Signed-off-by: Karsten Blees <blees@xxxxxxx>
---
Documentation/technical/api-hashmap.txt | 9 +++++++++
builtin/describe.c | 11 ++---------
decorate.c | 5 +----
diffcore-rename.c | 4 +---
hashmap.h | 11 +++++++++++
khash.h | 11 ++---------
object.c | 13 +------------
pack-objects.c | 5 ++---
8 files changed, 29 insertions(+), 40 deletions(-)
diff --git a/Documentation/technical/api-hashmap.txt b/Documentation/technical/api-hashmap.txt
index b977ae8..4689968 100644
--- a/Documentation/technical/api-hashmap.txt
+++ b/Documentation/technical/api-hashmap.txt
@@ -58,6 +58,15 @@ Functions
+
`strihash` and `memihash` are case insensitive versions.
+`unsigned int sha1hash(const unsigned char *sha1)`::
+
+ Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
+ for use in hash tables. Cryptographic hashes are supposed to have
+ uniform distribution, so in contrast to `memhash()`, this just copies
+ the first `sizeof(int)` bytes without shuffling any bits. Note that
+ the results will be different on big-endian and little-endian
+ platforms, so they should not be stored or transferred over the net!
+
`void hashmap_init(struct hashmap *map, hashmap_cmp_fn equals_function, size_t initial_size)`::
Initializes a hashmap structure.
diff --git a/builtin/describe.c b/builtin/describe.c
index 24d740c..57e84c8 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -56,17 +56,10 @@ static int commit_name_cmp(const struct commit_name *cn1,
return hashcmp(cn1->peeled, peeled ? peeled : cn2->peeled);
}
-static inline unsigned int hash_sha1(const unsigned char *sha1)
-{
- unsigned int hash;
- memcpy(&hash, sha1, sizeof(hash));
- return hash;
-}
-
static inline struct commit_name *find_commit_name(const unsigned char *peeled)
{
struct commit_name key;
- hashmap_entry_init(&key, hash_sha1(peeled));
+ hashmap_entry_init(&key, sha1hash(peeled));
return hashmap_get(&names, &key, peeled);
}
@@ -114,7 +107,7 @@ static void add_to_known_names(const char *path,
if (!e) {
e = xmalloc(sizeof(struct commit_name));
hashcpy(e->peeled, peeled);
- hashmap_entry_init(e, hash_sha1(peeled));
+ hashmap_entry_init(e, sha1hash(peeled));
hashmap_add(&names, e);
e->path = NULL;
}
diff --git a/decorate.c b/decorate.c
index 7cb5d29..b2aac90 100644
--- a/decorate.c
+++ b/decorate.c
@@ -8,10 +8,7 @@
static unsigned int hash_obj(const struct object *obj, unsigned int n)
{
- unsigned int hash;
-
- memcpy(&hash, obj->sha1, sizeof(unsigned int));
- return hash % n;
+ return sha1hash(obj->sha1) % n;
}
static void *insert_decoration(struct decoration *n, const struct object *base, void *decoration)
diff --git a/diffcore-rename.c b/diffcore-rename.c
index 749a35d..6fa97d4 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c
@@ -242,14 +242,12 @@ struct file_similarity {
static unsigned int hash_filespec(struct diff_filespec *filespec)
{
- unsigned int hash;
if (!filespec->sha1_valid) {
if (diff_populate_filespec(filespec, 0))
return 0;
hash_sha1_file(filespec->data, filespec->size, "blob", filespec->sha1);
}
- memcpy(&hash, filespec->sha1, sizeof(hash));
- return hash;
+ return sha1hash(filespec->sha1);
}
static int find_identical_files(struct hashmap *srcs,
diff --git a/hashmap.h b/hashmap.h
index a816ad4..ed5425a 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -13,6 +13,17 @@ 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);
+static inline unsigned int sha1hash(const unsigned char *sha1)
+{
+ /*
+ * Equivalent to 'return *(int *)sha1;', but safe on platforms that
+ * don't support unaligned reads.
+ */
+ unsigned int hash;
+ memcpy(&hash, sha1, sizeof(hash));
+ return hash;
+}
+
/* data structures */
struct hashmap_entry {
diff --git a/khash.h b/khash.h
index 57ff603..06c7906 100644
--- a/khash.h
+++ b/khash.h
@@ -320,19 +320,12 @@ static const double __ac_HASH_UPPER = 0.77;
code; \
} }
-static inline khint_t __kh_oid_hash(const unsigned char *oid)
-{
- khint_t hash;
- memcpy(&hash, oid, sizeof(hash));
- return hash;
-}
-
#define __kh_oid_cmp(a, b) (hashcmp(a, b) == 0)
-KHASH_INIT(sha1, const unsigned char *, void *, 1, __kh_oid_hash, __kh_oid_cmp)
+KHASH_INIT(sha1, const unsigned char *, void *, 1, sha1hash, __kh_oid_cmp)
typedef kh_sha1_t khash_sha1;
-KHASH_INIT(sha1_pos, const unsigned char *, int, 1, __kh_oid_hash, __kh_oid_cmp)
+KHASH_INIT(sha1_pos, const unsigned char *, int, 1, sha1hash, __kh_oid_cmp)
typedef kh_sha1_pos_t khash_sha1_pos;
#endif /* __AC_KHASH_H */
diff --git a/object.c b/object.c
index 57a0890..73acaea 100644
--- a/object.c
+++ b/object.c
@@ -50,18 +50,7 @@ int type_from_string(const char *str)
*/
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));
- return hash & (n - 1);
+ return sha1hash(sha1) & (n - 1);
}
/*
diff --git a/pack-objects.c b/pack-objects.c
index 4f36c32..9992f3e 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -7,10 +7,9 @@ static uint32_t locate_object_entry_hash(struct packing_data *pdata,
const unsigned char *sha1,
int *found)
{
- uint32_t i, hash, mask = (pdata->index_size - 1);
+ uint32_t i, mask = (pdata->index_size - 1);
- memcpy(&hash, sha1, sizeof(uint32_t));
- i = hash & mask;
+ i = sha1hash(sha1) & mask;
while (pdata->index[i] > 0) {
uint32_t pos = pdata->index[i] - 1;
--
1.9.4.msysgit.0.dirty
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