diff --git a/autotest/CountBits/CountBits.cpp b/autotest/CountBits/CountBits.cpp
new file mode 100644
index 000000000..40a5b73db
--- /dev/null
+++ b/autotest/CountBits/CountBits.cpp
@@ -0,0 +1,33 @@
+#include <Core/Core.h>
+
+using namespace Upp;
+
+CONSOLE_APP_MAIN
+{
+	StdLogSetup(LOG_FILE|LOG_COUT);
+	
+	DUMP(CountBits(0x0001));
+	DUMP(CountBits(0x000f));
+	DUMP(CountBits(0x00ff));
+	DUMP(CountBits(0x0fff));
+	DUMP(CountBits(0xffff));
+	DUMP(CountBits(0x000fffff));
+	DUMP(CountBits(0x00ffffff));
+	DUMP(CountBits(0x0fffffff));
+	DUMP(CountBits(0xffffffff));
+	
+	
+	LOG("====================");
+	
+	DUMP(CountBits64(0x00000001ffffffff));
+	DUMP(CountBits64(0x0000000fffffffff));
+	DUMP(CountBits64(0x000000ffffffffff));
+	DUMP(CountBits64(0x00000fffffffffff));
+	DUMP(CountBits64(0x0000ffffffffffff));
+	DUMP(CountBits64(0x000fffffffffffff));
+	DUMP(CountBits64(0x00ffffffffffffff));
+	DUMP(CountBits64(0x0fffffffffffffff));
+	DUMP(CountBits64(0xffffffffffffffff));
+	
+	CheckLogEtalon();
+}
diff --git a/autotest/CountBits/CountBits.upp b/autotest/CountBits/CountBits.upp
new file mode 100644
index 000000000..ceda0ff43
--- /dev/null
+++ b/autotest/CountBits/CountBits.upp
@@ -0,0 +1,10 @@
+uses
+	Core;
+
+file
+	Etalon.log,
+	CountBits.cpp;
+
+mainconfig
+	"" = "";
+
diff --git a/autotest/CountBits/Etalon.log b/autotest/CountBits/Etalon.log
new file mode 100644
index 000000000..3bf9570e1
--- /dev/null
+++ b/autotest/CountBits/Etalon.log
@@ -0,0 +1,21 @@
+* /home/maldoror//upp/.cache/upp.out/autotest/CLANG.Debug.Debug_Full.Shared/CountBits 08.02.2025 14:47:07, user: maldoror
+
+CountBits(0x0001) = 1
+CountBits(0x000f) = 4
+CountBits(0x00ff) = 8
+CountBits(0x0fff) = 12
+CountBits(0xffff) = 16
+CountBits(0x000fffff) = 20
+CountBits(0x00ffffff) = 24
+CountBits(0x0fffffff) = 28
+CountBits(0xffffffff) = 32
+====================
+CountBits64(0x00000001ffffffff) = 33
+CountBits64(0x0000000fffffffff) = 36
+CountBits64(0x000000ffffffffff) = 40
+CountBits64(0x00000fffffffffff) = 44
+CountBits64(0x0000ffffffffffff) = 48
+CountBits64(0x000fffffffffffff) = 52
+CountBits64(0x00ffffffffffffff) = 56
+CountBits64(0x0fffffffffffffff) = 60
+CountBits64(0xffffffffffffffff) = 64
diff --git a/uppsrc/Core/Ops.h b/uppsrc/Core/Ops.h
index dc36a13f2..a4017f40f 100644
--- a/uppsrc/Core/Ops.h
+++ b/uppsrc/Core/Ops.h
@@ -202,6 +202,47 @@ inline bool FitsInInt64(double x)
 	return x >= -9223372036854775808.0 && x < 9223372036854775808.0;
 }
 
+force_inline
+int CountBits(dword mask)
+{
+#if defined(__GNUC__) || defined(__clang__)
+    return __builtin_popcount(mask);
+#elif defined(_MSC_VER)
+    return __popcnt(mask);
+#else
+    // Fallback (unlikely)
+    mask = mask - ((mask >> 1) & 0x55555555);
+    mask = (mask & 0x33333333) + ((mask >> 2) & 0x33333333);
+    mask = (mask + (mask >> 4)) & 0x0F0F0F0F;
+    mask = mask + (mask >> 8);
+    mask = mask + (mask >> 16);
+    return mask & 0x3F;
+#endif
+}
+
+force_inline
+int CountBits64(uint64 mask)
+{
+#if defined(__GNUC__) || defined(__clang__)
+    return __builtin_popcountll(mask);
+#elif defined(_MSC_VER)
+    #if defined(_WIN64)
+        return __popcnt64(mask);
+    #else
+        return CountBits(static_cast<dword>(mask)) +  CountBits(static_cast<dword>(mask >> 32));
+    #endif
+#else
+    // Fallback (unlikely)
+    mask = mask - ((mask >> 1) & 0x5555555555555555ULL);
+    mask = (mask & 0x3333333333333333ULL) + ((mask >> 2) & 0x3333333333333333ULL);
+    mask = (mask + (mask >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
+    mask = mask + (mask >> 8);
+    mask = mask + (mask >> 16);
+    mask = mask + (mask >> 32);
+    return mask & 0x7F;
+#endif
+}
+
 #if defined(__SIZEOF_INT128__) && (__GNUC__ > 5 || __clang_major__ >= 5)
 
 #ifdef CPU_X86
diff --git a/uppsrc/Core/src.tpp/Mem_en-us.tpp b/uppsrc/Core/src.tpp/Mem_en-us.tpp
index 3f6703e6a..a5a6b3b33 100644
--- a/uppsrc/Core/src.tpp/Mem_en-us.tpp
+++ b/uppsrc/Core/src.tpp/Mem_en-us.tpp
@@ -132,6 +132,13 @@ for binary value 1010, this value is 4. For 0, the value is 0.&]
 loosing the precision.&]
 [s3;%% &]
 [s4; &]
+[s5;:Upp`:`:CountBits`(dword`): [@(0.0.255) int] [* CountBits]([_^Upp`:`:dword^ dword] 
+[*@3 mask])&]
+[s5;:Upp`:`:CountBits64`(uint64`): [@(0.0.255) int] [* CountBits64]([_^Upp`:`:uint64^ uint6
+4] [*@3 mask])&]
+[s2;%% Returns the total number of set bits in a given bit [%-*@3 mask].&]
+[s3; &]
+[s4; &]
 [s5;:Upp`:`:Peek16le`(const void`*`): [@(0.0.255) int]_[* Peek16le]([@(0.0.255) const]_[@(0.0.255) v
 oid]_`*[*@3 ptr])&]
 [s5;:Upp`:`:Peek32le`(const void`*`): [@(0.0.255) int]_[* Peek32le]([@(0.0.255) const]_[@(0.0.255) v