Subject: [PATCH 1/4] hashmap: introduce memhash_feed to access the internals of FNV-1 hash

From: Stefan Beller <[email-masked]>
Date: Tue, 24 Oct 2017 11:59:14 -0700

This will be useful shortly.

Signed-off-by: Stefan Beller <[email-masked]>
---
 hashmap.c | 7 ++++++-
 hashmap.h | 3 +++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/hashmap.c b/hashmap.c
index d42f01ff5a..d103eb1fd2 100644
--- a/hashmap.c
+++ b/hashmap.c
@@ -26,13 +26,18 @@ unsigned int strihash(const char *str)
 	return hash;
 }
 
+unsigned int memhash_feed(unsigned int hash_seed, const unsigned char next)
+{
+	return (hash_seed * FNV32_PRIME) ^ next;
+}
+
 unsigned int memhash(const void *buf, size_t len)
 {
 	unsigned int hash = FNV32_BASE;
 	unsigned char *ucbuf = (unsigned char *) buf;
 	while (len--) {
 		unsigned int c = *ucbuf++;
-		hash = (hash * FNV32_PRIME) ^ c;
+		hash = memhash_feed(hash, c);
 	}
 	return hash;
 }
diff --git a/hashmap.h b/hashmap.h
index 7cb29a6aed..c2464385ed 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -105,10 +105,13 @@
  * `strihash` and `memihash` are case insensitive versions.
  * `memihash_cont` is a variant of `memihash` that allows a computation to be
  * continued with another chunk of data.
+ * `memhash_feed` takes just one character and returns the hash based off
+ * a previous hash.
  */
 extern unsigned int strhash(const char *buf);
 extern unsigned int strihash(const char *buf);
 extern unsigned int memhash(const void *buf, size_t len);
+extern unsigned int memhash_feed(unsigned int hash_seed, const unsigned char next);
 extern unsigned int memihash(const void *buf, size_t len);
 extern unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
 
-- 
2.15.0.rc2.6.g953226eb5f