hash: add a function to lookup hash algorithm by length

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 <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/hash.h b/hash.h
index adde708cf26d90ffd7ae10e6cdb8bfd7c08b1db5..661c9f228128c2036fa4c5c238f2e35f9a42f13b 100644 (file)
--- 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
index 494606f7716923468e6f838dae0486a61b454101..bcd9470bce089012ab942973cd841262d35749eb 100644 (file)
--- 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