From dcd75a4f09839e727598e5001bed4330e3e55500 Mon Sep 17 00:00:00 2001
From: Philip Rebohle <philip.rebohle@tu-dortmund.de>
Date: Thu, 9 May 2019 16:37:45 +0200
Subject: [PATCH] [util] Optimize popcnt operation

---
 src/util/util_bit.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/util/util_bit.h b/src/util/util_bit.h
index 9d9cdfc3..7a6fe347 100644
--- a/src/util/util_bit.h
+++ b/src/util/util_bit.h
@@ -14,12 +14,18 @@ namespace dxvk::bit {
   T extract(T value, uint32_t fst, uint32_t lst) {
     return (value >> fst) & ~(~T(0) << (lst - fst + 1));
   }
+
+  inline uint32_t popcntStep(uint32_t n, uint32_t mask, uint32_t shift) {
+    return (n & mask) + ((n & ~mask) >> shift);
+  }
   
-  template<typename T>
-  T popcnt(T value) {
-    return value != 0
-      ? (value & 1) + popcnt(value >> 1)
-      : 0;
+  inline uint32_t popcnt(uint32_t n) {
+    n = popcntStep(n, 0x55555555, 1);
+    n = popcntStep(n, 0x33333333, 2);
+    n = popcntStep(n, 0x0F0F0F0F, 4);
+    n = popcntStep(n, 0x00FF00FF, 8);
+    n = popcntStep(n, 0x0000FFFF, 16);
+    return n;
   }
   
   inline uint32_t tzcnt(uint32_t n) {