hash: add a function to lookup hash algorithm by length

bk2204 · gitster · commit 95399788d158 · 2019-04-01T11:57:39.000+09:00
There are some cases, such as the dumb HTTP transport and bundles, where
we can only determine the hash algorithm in use by the length of the
object IDs. Provide a function that looks up the algorithm by length.

Signed-off-by: brian m. carlson &lt;sandals@crustytoothpaste.net&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/hash.h b/hash.h
@@ -131,6 +131,8 @@ extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];
 int hash_algo_by_name(const char *name);
 /* Identical, except based on the format ID. */
 int hash_algo_by_id(uint32_t format_id);
+/* Identical, except based on the length. */
+int hash_algo_by_length(int len);
 /* Identical, except for a pointer to struct git_hash_algo. */
 static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
 {
diff --git a/sha1-file.c b/sha1-file.c
@@ -189,6 +189,14 @@ int hash_algo_by_id(uint32_t format_id)
 	return GIT_HASH_UNKNOWN;
 }
 
+int hash_algo_by_length(int len)
+{
+	int i;
+	for (i = 1; i < GIT_HASH_NALGOS; i++)
+		if (len == hash_algos[i].rawsz)
+			return i;
+	return GIT_HASH_UNKNOWN;
+}
 
 /*
  * This is meant to hold a *small* number of objects that you would

Original file line number	Diff line number	Diff line change
`@@ -131,6 +131,8 @@ extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];`
`131`	`131`	`int hash_algo_by_name(const char *name);`
`132`	`132`	`/* Identical, except based on the format ID. */`
`133`	`133`	`int hash_algo_by_id(uint32_t format_id);`
	`134`	`+/* Identical, except based on the length. */`
	`135`	`+int hash_algo_by_length(int len);`
`134`	`136`	`/* Identical, except for a pointer to struct git_hash_algo. */`
`135`	`137`	`static inline int hash_algo_by_ptr(const struct git_hash_algo *p)`
`136`	`138`	`{`