From b3f6a2415e525b68c7893d36cb7d224e02646872 Mon Sep 17 00:00:00 2001
From: Andrii Mytroshyn <retsetA@gmail.com>
Date: Wed, 1 Jan 2025 22:20:39 +0200
Subject: [PATCH] Optimize while loop to use 4 elements instead of 7 for
 calculation, improving performance on older CPUs

---
 src/bitops.c | 29 +++++++++--------------------
 1 file changed, 9 insertions(+), 20 deletions(-)

diff --git a/src/bitops.c b/src/bitops.c
index 44312c6af..0caaea881 100644
--- a/src/bitops.c
+++ b/src/bitops.c
@@ -59,41 +59,30 @@ long long redisPopcount(void *s, long count) {
         goto remain;
     }
 
-    /* Count bits 28 bytes at a time */
+    /* Count bits 16 bytes at a time */
     p4 = (uint32_t*)p;
-    while(count>=28) {
-        uint32_t aux1, aux2, aux3, aux4, aux5, aux6, aux7;
+    while(count>=16) {
+        uint32_t aux1, aux2, aux3, aux4;
 
         aux1 = *p4++;
         aux2 = *p4++;
         aux3 = *p4++;
         aux4 = *p4++;
-        aux5 = *p4++;
-        aux6 = *p4++;
-        aux7 = *p4++;
-        count -= 28;
+        count -= 16;
 
         aux1 = aux1 - ((aux1 >> 1) & 0x55555555);
         aux1 = (aux1 & 0x33333333) + ((aux1 >> 2) & 0x33333333);
+        aux1 = (aux1 + (aux1 >> 4)) & 0x0F0F0F0F;
         aux2 = aux2 - ((aux2 >> 1) & 0x55555555);
         aux2 = (aux2 & 0x33333333) + ((aux2 >> 2) & 0x33333333);
+        aux2 = (aux2 + (aux2 >> 4)) & 0x0F0F0F0F;
         aux3 = aux3 - ((aux3 >> 1) & 0x55555555);
         aux3 = (aux3 & 0x33333333) + ((aux3 >> 2) & 0x33333333);
+        aux3 = (aux3 + (aux3 >> 4)) & 0x0F0F0F0F;
         aux4 = aux4 - ((aux4 >> 1) & 0x55555555);
         aux4 = (aux4 & 0x33333333) + ((aux4 >> 2) & 0x33333333);
-        aux5 = aux5 - ((aux5 >> 1) & 0x55555555);
-        aux5 = (aux5 & 0x33333333) + ((aux5 >> 2) & 0x33333333);
-        aux6 = aux6 - ((aux6 >> 1) & 0x55555555);
-        aux6 = (aux6 & 0x33333333) + ((aux6 >> 2) & 0x33333333);
-        aux7 = aux7 - ((aux7 >> 1) & 0x55555555);
-        aux7 = (aux7 & 0x33333333) + ((aux7 >> 2) & 0x33333333);
-        bits += ((((aux1 + (aux1 >> 4)) & 0x0F0F0F0F) +
-                    ((aux2 + (aux2 >> 4)) & 0x0F0F0F0F) +
-                    ((aux3 + (aux3 >> 4)) & 0x0F0F0F0F) +
-                    ((aux4 + (aux4 >> 4)) & 0x0F0F0F0F) +
-                    ((aux5 + (aux5 >> 4)) & 0x0F0F0F0F) +
-                    ((aux6 + (aux6 >> 4)) & 0x0F0F0F0F) +
-                    ((aux7 + (aux7 >> 4)) & 0x0F0F0F0F))* 0x01010101) >> 24;
+        aux4 = (aux4 + (aux4 >> 4)) & 0x0F0F0F0F;
+        bits += ((aux1 + aux2 + aux3 + aux4)* 0x01010101) >> 24;
     }
     p = (unsigned char*)p4;