[PATCH v2 26/35] hash: add a function to lookup hash algorithm by length

["brian m. carlson" <sandals@crustytoothpaste.net>]

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>
---
 hash.h      | 2 ++
 sha1-file.c | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/hash.h b/hash.h
index adde708cf2..661c9f2281 100644
--- 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 494606f771..bcd9470bce 100644
--- 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