From 2cd20d3c4c68e34672ce625f7bd172df7b4455d7 Mon Sep 17 00:00:00 2001 From: antirez Date: Thu, 17 Apr 2014 18:02:45 +0200 Subject: [PATCH] Speedup hllRawSum() processing 8 bytes per iteration. The internal HLL raw encoding used by PFCOUNT when merging multiple keys is aligned to 8 bits (1 byte per register) so we can exploit this to improve performances by processing multiple bytes per iteration. In benchmarks the new code was several times faster with HLLs with many registers set to zero, while no slowdown was observed with populated HLLs. --- src/hyperloglog.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/src/hyperloglog.c b/src/hyperloglog.c index c951c09f..1c6ed45f 100644 --- a/src/hyperloglog.c +++ b/src/hyperloglog.c @@ -928,16 +928,24 @@ double hllSparseSum(uint8_t *sparse, int sparselen, double *PE, int *ezp, int *i double hllRawSum(uint8_t *registers, double *PE, int *ezp) { double E = 0; int j, ez = 0; - unsigned long reg; + uint64_t *word = (uint64_t*) registers; + uint8_t *bytes; - for (j = 0; j < HLL_REGISTERS; j++) { - reg = registers[j]; - if (reg == 0) { - ez++; - /* Increment E at the end of the loop. */ + for (j = 0; j < HLL_REGISTERS/8; j++) { + if (*word == 0) { + ez += 8; } else { - E += PE[reg]; /* Precomputed 2^(-reg[j]). */ + bytes = (uint8_t*) word; + if (bytes[0]) E += PE[bytes[0]]; else ez++; + if (bytes[1]) E += PE[bytes[1]]; else ez++; + if (bytes[2]) E += PE[bytes[2]]; else ez++; + if (bytes[3]) E += PE[bytes[3]]; else ez++; + if (bytes[4]) E += PE[bytes[4]]; else ez++; + if (bytes[5]) E += PE[bytes[5]]; else ez++; + if (bytes[6]) E += PE[bytes[6]]; else ez++; + if (bytes[7]) E += PE[bytes[7]]; else ez++; } + word++; } E += ez; /* 2^(-reg[j]) is 1 when m is 0, add it 'ez' times for every zero register in the HLL. */