use murmur3_32 hash

it is more efficient than the previously used djb hash

1 files changed, 45 insertions, 6 deletions

diff --git a/src/blob.c b/src/blob.c
index 007a0cd..6a2fe92 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -200,17 +200,56 @@ apk_blob_t apk_blob_pushed(apk_blob_t buffer, apk_blob_t left)
 	return APK_BLOB_PTR_LEN(buffer.ptr, left.ptr - buffer.ptr);
 }
 
-unsigned long apk_blob_hash_seed(apk_blob_t blob, unsigned long seed)
-{
-	unsigned long hash = seed;
+static uint32_t murmur3_32(const char *key, uint32_t len, uint32_t seed)
+{
+	static const uint32_t c1 = 0xcc9e2d51;
+	static const uint32_t c2 = 0x1b873593;
+	static const uint32_t r1 = 15;
+	static const uint32_t r2 = 13;
+	static const uint32_t m = 5;
+	static const uint32_t n = 0xe6546b64;
+	uint32_t hash = seed;
+	const int nblocks = len / 4;
+	const uint32_t *blocks = (const uint32_t *) key;
 	int i;
+	for (i = 0; i < nblocks; i++) {
+		uint32_t k = blocks[i];
+		k *= c1;
+		k = (k << r1) | (k >> (32 - r1));
+		k *= c2;
+		hash ^= k;
+		hash = ((hash << r2) | (hash >> (32 - r2))) * m + n;
+	}
 
-        for (i = 0; i < blob.len; i++)
-		hash = hash * 33 + blob.ptr[i];
-
+	const uint8_t *tail = (const uint8_t *) (key + nblocks * 4);
+	uint32_t k1 = 0;
+
+	switch (len & 3) {
+	case 3:
+		k1 ^= tail[2] << 16;
+	case 2:
+		k1 ^= tail[1] << 8;
+	case 1:
+		k1 ^= tail[0];
+		k1 *= c1;
+		k1 = (k1 << r1) | (k1 >> (32 - r1));
+		k1 *= c2;
+		hash ^= k1;
+	}
+	hash ^= len;
+	hash ^= (hash >> 16);
+	hash *= 0x85ebca6b;
+	hash ^= (hash >> 13);
+	hash *= 0xc2b2ae35;
+	hash ^= (hash >> 16);
 	return hash;
 }
 
+unsigned long apk_blob_hash_seed(apk_blob_t blob, unsigned long seed)
+{
+	return murmur3_32(blob.ptr, blob.len, seed);
+}
+
 unsigned long apk_blob_hash(apk_blob_t blob)
 {
 	return apk_blob_hash_seed(blob, 5381);