diff options
Diffstat (limited to 'src/siphash.c')
| -rw-r--r-- | src/siphash.c | 29 |
1 files changed, 15 insertions, 14 deletions
diff --git a/src/siphash.c b/src/siphash.c index 7219d4b88..6c41fe6b6 100644 --- a/src/siphash.c +++ b/src/siphash.c @@ -19,18 +19,23 @@ This version was modified by Salvatore Sanfilippo <antirez@gmail.com> in the following ways: - 1. Hard-code 2-4 rounds in the hope the compiler can optimize it more + 1. We use SipHash 1-2. This is not believed to be as strong as the + suggested 2-4 variant, but AFAIK there are not trivial attacks + against this reduced-rounds version, and it runs at the same speed + as Murmurhash2 that we used previously, why the 2-4 variant slowed + down Redis by a 4% figure more or less. + 2. Hard-code rounds in the hope the compiler can optimize it more in this raw from. Anyway we always want the standard 2-4 variant. - 2. Modify the prototype and implementation so that the function directly + 3. Modify the prototype and implementation so that the function directly returns an uint64_t value, the hash itself, instead of receiving an output buffer. This also means that the output size is set to 8 bytes and the 16 bytes output code handling was removed. - 3. Provide a case insensitive variant to be used when hashing strings that + 4. Provide a case insensitive variant to be used when hashing strings that must be considered identical by the hash table regardless of the case. If we don't have directly a case insensitive hash function, we need to perform a text transformation in some temporary buffer, which is costly. - 4. Remove debugging code. - 5. Modified the original test.c file to be a stand-alone function testing + 5. Remove debugging code. + 6. Modified the original test.c file to be a stand-alone function testing the function in the new form (returing an uint64_t) using just the relevant test vector. */ @@ -132,7 +137,6 @@ uint64_t siphash(const uint8_t *in, const size_t inlen, const uint8_t *k) { v3 ^= m; SIPROUND; - SIPROUND; v0 ^= m; } @@ -151,15 +155,12 @@ uint64_t siphash(const uint8_t *in, const size_t inlen, const uint8_t *k) { v3 ^= b; SIPROUND; - SIPROUND; v0 ^= b; v2 ^= 0xff; SIPROUND; SIPROUND; - SIPROUND; - SIPROUND; b = v0 ^ v1 ^ v2 ^ v3; #ifndef UNALIGNED_LE_CPU @@ -196,7 +197,6 @@ uint64_t siphash_nocase(const uint8_t *in, const size_t inlen, const uint8_t *k) v3 ^= m; SIPROUND; - SIPROUND; v0 ^= m; } @@ -215,15 +215,12 @@ uint64_t siphash_nocase(const uint8_t *in, const size_t inlen, const uint8_t *k) v3 ^= b; SIPROUND; - SIPROUND; v0 ^= b; v2 ^= 0xff; SIPROUND; SIPROUND; - SIPROUND; - SIPROUND; b = v0 ^ v1 ^ v2 ^ v3; #ifndef UNALIGNED_LE_CPU @@ -308,7 +305,11 @@ const uint8_t vectors_sip64[64][8] = { /* Test siphash using a test vector. Returns 0 if the function passed - * all the tests, otherwise 1 is returned. */ + * all the tests, otherwise 1 is returned. + * + * IMPORTANT: The test vector is for SipHash 2-4. Before running + * the test revert back the siphash() function to 2-4 rounds since + * now it uses 1-2 rounds. */ int siphash_test(void) { uint8_t in[64], k[16]; int i; |