From fd734f387d8780d9989d750942d026167de8cf3c Mon Sep 17 00:00:00 2001 From: Jeff Davis Date: Thu, 30 Jul 2020 08:44:58 -0700 Subject: [PATCH] Use pg_bitutils for HyperLogLog. Using pg_leftmost_one_post32() yields substantial performance benefits. Backpatching to version 13 because HLL is used for HashAgg improvements in 9878b643, which was also backpatched to 13. Reviewed-by: Peter Geoghegan Discussion: https://postgr.es/m/CAH2-WzkGvDKVDo+0YvfvZ+1CE=iCi88DCOGFF3i1hTGGaxcKPw@mail.gmail.com Backpatch-through: 13 --- src/backend/lib/hyperloglog.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/src/backend/lib/hyperloglog.c b/src/backend/lib/hyperloglog.c index a5cc1f8b83b..351fed8186f 100644 --- a/src/backend/lib/hyperloglog.c +++ b/src/backend/lib/hyperloglog.c @@ -49,6 +49,7 @@ #include #include "lib/hyperloglog.h" +#include "port/pg_bitutils.h" #define POW_2_32 (4294967296.0) #define NEG_POW_2_32 (-4294967296.0) @@ -242,11 +243,13 @@ rho(uint32 x, uint8 b) { uint8 j = 1; - while (j <= b && !(x & 0x80000000)) - { - j++; - x <<= 1; - } + if (x == 0) + return b + 1; + + j = 32 - pg_leftmost_one_pos32(x); + + if (j > b) + return b + 1; return j; }