From bd62a91d03034f9f1600b6994b7f3cff2f76bc7d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Fri, 28 Apr 2023 12:01:21 -0600
Subject: [PATCH] [algs] 64bit popcount

---
 src/hb-algs.hh | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/hb-algs.hh b/src/hb-algs.hh
index 13587eac0..faf467c76 100644
--- a/src/hb-algs.hh
+++ b/src/hb-algs.hh
@@ -618,16 +618,18 @@ hb_popcount (T v)
   if (sizeof (T) <= 4)
   {
     /* "HACKMEM 169" */
-    uint32_t y;
-    y = (v >> 1) &033333333333;
+    uint32_t y = (uint32_t) v;
+    y = (y >> 1) &033333333333;
     y = v - y - ((y >>1) & 033333333333);
     return (((y + (y >> 3)) & 030707070707) % 077);
   }
 
   if (sizeof (T) == 8)
   {
-    unsigned int shift = 32;
-    return hb_popcount<uint32_t> ((uint32_t) v) + hb_popcount ((uint32_t) (v >> shift));
+    uint64_t y = (uint64_t) v;
+    y -= ((y >> 1) & 0x5555555555555555ull);
+    y = (y & 0x3333333333333333ull) + (y >> 2 & 0x3333333333333333ull);
+    return ((y + (y >> 4)) & 0xf0f0f0f0f0f0f0full) * 0x101010101010101ull >> 56;
   }
 
   if (sizeof (T) == 16)