From 93eb35a61862e0f070bb49f9d92f019e6dab5fe8 Mon Sep 17 00:00:00 2001
From: Vladislav Belov <vladislavbelovdev@gmail.com>
Date: Mon, 21 Sep 2026 00:47:09 +0200
Subject: [PATCH] Replaces PopulationCount by std::popcount

---
 source/lib/bits.h                  | 39 +-----------------------------
 source/lib/sysdep/os/win/wcpu.cpp  |  6 +++--
 source/lib/sysdep/os/win/wnuma.cpp |  7 +++---
 source/lib/tests/test_bits.h       | 20 +--------------
 4 files changed, 10 insertions(+), 62 deletions(-)

diff --git a/source/lib/bits.h b/source/lib/bits.h
index cb85763af2..69f3908fea 100644
--- a/source/lib/bits.h
+++ b/source/lib/bits.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -128,43 +128,6 @@ inline T SetBitsTo(T num, size_t lo_idx, size_t hi_idx, size_t value)
 	return result;
 }
 
-
-/**
- * @return number of 1-bits in mask.
- * execution time is proportional to number of 1-bits in mask.
- **/
-template<typename T>
-inline size_t SparsePopulationCount(T mask)
-{
-	size_t num1Bits = 0;
-	while(mask)
-	{
-		mask &= mask-1; // clear least significant 1-bit
-		num1Bits++;
-	}
-
-	return num1Bits;
-}
-
-/**
- * @return number of 1-bits in mask.
- * execution time is logarithmic in the total number of bits.
- * supports up to 128-bit integers (if their arithmetic operators are defined).
- * [http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel]
- **/
-template<typename T>
-static inline size_t PopulationCount(T x)
-{
-	cassert(!std::numeric_limits<T>::is_signed);
-	const T mask = T(~T(0));
-	x -= (x >> 1) & (mask/3);	// count 2 bits
-	x = (x & (mask/15*3)) + ((x >> 2) & (mask/15*3));	// count 4 bits
-	x = (x + (x >> 4)) & (mask/255*15);	// count 8 bits
-	return T(x * (mask/255)) >> ((sizeof(T)-1)*CHAR_BIT);
-}
-
-
-
 /**
  * @return whether the given number is a power of two.
  **/
diff --git a/source/lib/sysdep/os/win/wcpu.cpp b/source/lib/sysdep/os/win/wcpu.cpp
index 3958ca6ac2..b9064be995 100644
--- a/source/lib/sysdep/os/win/wcpu.cpp
+++ b/source/lib/sysdep/os/win/wcpu.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2014 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -34,6 +34,8 @@
 #include "lib/sysdep/os/win/wutil.h"
 #include "lib/sysdep/arch/x86_x64/x86_x64.h"
 
+#include <bit>
+
 
 uintptr_t os_cpu_ProcessorMask()
 {
@@ -59,7 +61,7 @@ size_t os_cpu_NumProcessors()
 
 	if(!numProcessors)
 	{
-		numProcessors = PopulationCount(os_cpu_ProcessorMask());
+		numProcessors = std::popcount(os_cpu_ProcessorMask());
 
 		// sanity check
 		SYSTEM_INFO si;
diff --git a/source/lib/sysdep/os/win/wnuma.cpp b/source/lib/sysdep/os/win/wnuma.cpp
index cf1ff808eb..91f768a18a 100644
--- a/source/lib/sysdep/os/win/wnuma.cpp
+++ b/source/lib/sysdep/os/win/wnuma.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,7 +23,7 @@
 #include "precompiled.h"
 #include "lib/sysdep/numa.h"
 
-#include "lib/bits.h"	// PopulationCount
+#include "lib/bits.h"
 #include "lib/alignment.h"
 #include "lib/lib.h"
 #include "lib/timer.h"
@@ -35,6 +35,7 @@
 #include "lib/sysdep/os/win/wutil.h"
 #include "lib/sysdep/os/win/wcpu.h"
 
+#include <bit>
 #include <map>
 #include <Psapi.h>
 #include <utility>
@@ -117,7 +118,7 @@ static void PopulateNodes()
 		const BOOL ok = GetProcessAffinityMask(GetCurrentProcess(), &processAffinity, &systemAffinity);
 		WARN_IF_FALSE(ok);
 	}
-	ENSURE(PopulationCount(processAffinity) <= PopulationCount(systemAffinity));
+	ENSURE(std::popcount(processAffinity) <= std::popcount(systemAffinity));
 
 	for(UCHAR nodeNumber = 0; nodeNumber <= HighestNodeNumber(); nodeNumber++)
 	{
diff --git a/source/lib/tests/test_bits.h b/source/lib/tests/test_bits.h
index 088c9ab496..0e974c7ceb 100644
--- a/source/lib/tests/test_bits.h
+++ b/source/lib/tests/test_bits.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2025 Wildfire Games.
+/* Copyright (C) 2026 Wildfire Games.
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -85,24 +85,6 @@ public:
 		EQUALS(bits<u64>(0xA5A5A5A5A5A5A5A5ull, 32, 63), 0xA5A5A5A5ull);
 	}
 
-	void test_PopulationCount()
-	{
-		EQUALS(PopulationCount<u8>(0), 0u);
-		EQUALS(PopulationCount<u8>(4), 1u);
-		EQUALS(PopulationCount<u8>(0x28), 2u);
-		EQUALS(PopulationCount<u8>(0xFF), 8u);
-		EQUALS(PopulationCount<u32>(0x0ul), 0u);
-		EQUALS(PopulationCount<u32>(0x8ul), 1u);
-		EQUALS(PopulationCount<u32>(0xFFFFul), 16u);
-		EQUALS(PopulationCount<u32>(0xFFFFFFFFul), 32u);
-		EQUALS(PopulationCount<u64>(0x0ull), 0u);
-		EQUALS(PopulationCount<u64>(0x10ull), 1u);
-		EQUALS(PopulationCount<u64>(0xFFFFull), 16u);
-		EQUALS(PopulationCount<u64>(0xFFFFFFFFull), 32u);
-		EQUALS(PopulationCount<u64>(0xFFFFFFFFFFFFFFFEull), 63u);
-		EQUALS(PopulationCount<u64>(0xFFFFFFFFFFFFFFFFull), 64u);
-	}
-
 	void test_is_pow2()
 	{
 		EQUALS(is_pow2(0u), false);