diff --git a/BeefLibs/corlib/src/Bitfield.bf b/BeefLibs/corlib/src/Bitfield.bf
new file mode 100644
index 00000000..319db448
--- /dev/null
+++ b/BeefLibs/corlib/src/Bitfield.bf
@@ -0,0 +1,279 @@
+using System.Reflection;
+using System.Diagnostics;
+
+namespace System
+{
+	[AttributeUsage(.Field | .StaticField)]
+	struct BitfieldAttribute : Attribute, IOnFieldInit
+	{
+		public enum BitSpec
+		{
+			case Auto;
+			case AutoAt(int pos);
+			case AutoRev;
+			case Bits(int bits);
+			case BitsRev(int bits);
+			case BitsAt(int bits, int pos);
+			case BitRange(IndexRange range);
+			case ValueRange(Range range);
+			case ValueRangeRev(Range range);
+			case ValueRangeAt(Range range, int pos);
+		}
+
+		public enum ProtectionKind
+		{
+			Private = 0,
+			Public = 1,
+			Protected = 2,
+		}
+
+		public enum AccessFlags
+		{
+			Read = 1,
+			Write = 2
+		}
+
+		protected String mName;
+		protected int32 mBitPos = -1;
+		protected BitSpec mBitSpec;
+		protected int32 mFieldIdx = 0;
+		protected Type mBFieldType = null;
+		protected ProtectionKind mProtection;
+		protected AccessFlags mAccessFlags;
+
+		public this(ProtectionKind protection, BitSpec bitSpec, String name, AccessFlags accessFlags = .Read | .Write)
+		{
+			mName = name;
+			mBitSpec = bitSpec;
+			mProtection = protection;
+			mAccessFlags = accessFlags;
+		}
+
+		[Comptime]
+		public void OnFieldInit(ComptimeFieldInfo fieldInfo, Self* prev) mut
+		{
+			if (mBFieldType == null)
+				mBFieldType = fieldInfo.FieldType;
+			var buType = mBFieldType;
+			if (buType.IsEnum)
+				buType = buType.UnderlyingType;
+
+			if (buType.IsFloatingPoint)
+				Runtime.FatalError("Invalid bitfield type");
+
+			bool isRev = false;
+			int32 bitCount = 0;
+			int32 underlyingBitCount = fieldInfo.FieldType.Size * 8;
+
+			int32 GetBitSize(int min, int max)
+			{
+				var min;
+				var max;
+				if (min < 0)
+					min = ~min;
+				if (max < 0)
+					max = ~max;
+				uint64 value = (uint64)min | (uint64)max;
+
+				int32 bitCount = 1;
+				if (buType.IsSigned)
+					bitCount++;
+
+				while ((value >>= 1) != 0)
+					bitCount++;
+
+				return bitCount;
+			}
+
+			bool hasRange = false;
+			bool rangeCheckMin = false;
+			bool rangeCheckMax = false;
+			int minVal = 0;
+			int maxVal = 0;
+
+			switch (mBitSpec)
+			{
+			case .Bits(let bits):
+				bitCount = (.)bits;
+			case .BitsRev(let bits):
+				bitCount = (.)bits;
+				isRev = true;
+			case .BitsAt(let bits, let pos):
+				bitCount = (.)bits;
+				mBitPos = (.)pos;
+			case .BitRange(let range):
+				bitCount = (.)range.GetLength(underlyingBitCount);
+				mBitPos = (.)range.Start.Get(underlyingBitCount);
+			case .ValueRange(let range):
+				minVal = range.Start;
+				maxVal = range.End - 1;
+				hasRange = true;
+				bitCount = GetBitSize(minVal, maxVal);
+			case .ValueRangeRev(let range):
+				minVal = range.Start;
+				maxVal = range.End - 1;
+				hasRange = true;
+				bitCount = GetBitSize(minVal, maxVal);
+				isRev = true;
+			case .ValueRangeAt(let range, int pos):
+				bitCount = GetBitSize(range.Start, range.End - 1);
+				bitCount = (.)pos;
+			default:
+				Runtime.FatalError("Invalid bitspec");
+			}
+
+			if ((prev != null) && (prev.mFieldIdx == fieldInfo.FieldIdx))
+			{
+				if (mBitPos == -1)
+				{
+					mBitPos = prev.mBitPos;
+					if (isRev)
+						mBitPos -= bitCount;
+				}
+			}
+
+			if (mBitPos == -1)
+				mBitPos = isRev ? underlyingBitCount - bitCount : 0;
+
+			if (Compiler.IsBuilding)
+				Debug.WriteLine($"OnFieldInit Name:{mName} BitPos:{mBitPos} BitCount:{bitCount} BuType:{buType}");
+
+			int bitSize = fieldInfo.FieldType.Size * 8;
+			if ((mBitPos < 0) || (mBitPos + bitCount > bitSize))
+				Runtime.FatalError("Bitfield exceeds bounds of underlying value");
+
+			String str = scope .();
+			if (mProtection == .Public)
+				str.Append("public ");
+			else if (mProtection == .Protected)
+				str.Append("protected ");
+
+			void TypeStr(String str, Type t)
+			{
+				if (t.IsPrimitive)
+					t.GetFullName(str);
+				else
+					str.AppendF($"comptype({(int)t.TypeId})");
+			}
+
+			String uTypeStr = TypeStr(.. scope .(), fieldInfo.FieldType);
+			String bTypeStr = TypeStr(.. scope .(), mBFieldType);
+			int mask = ((1 << mBitPos) << bitCount) - (1 << mBitPos);
+
+			if ((!hasRange) && (mBFieldType.IsSigned))
+			{
+				minVal = -(1<<(bitCount-1));
+				maxVal = (1<<(bitCount-1))-1;
+			}
+			else if (!hasRange)
+			{
+				maxVal = (1<<(bitCount))-1;
+			}
+
+			str.AppendF($"{bTypeStr} {mName}\n{{\n");
+
+			if (mAccessFlags.HasFlag(.Read))
+			{
+				str.Append("\t[Inline]\n\tget => ");
+				if (mBFieldType == typeof(bool))
+					str.AppendF($"(({fieldInfo.Name} & {mask}) >> {mBitPos}) != 0;\n");
+				else if (buType.IsSigned)
+					str.AppendF($"(.)((int)((({fieldInfo.Name} & 0x{mask:X}) >> {mBitPos}) ^ 0x{1 << (bitCount - 1):X}) - 0x{1 << (bitCount - 1):X});\n");
+				else
+					str.AppendF($"(.)(({fieldInfo.Name} & 0x{mask:X}) >> {mBitPos});\n");
+			}
+
+			if (mBFieldType.IsInteger)
+			{
+				if (mBFieldType.IsSigned)
+				{
+					rangeCheckMin = minVal != -(1<<(mBFieldType.Size*8-1));
+					rangeCheckMax = maxVal != (1<<(mBFieldType.Size*8-1))-1;
+				}
+				else
+				{
+					rangeCheckMin = minVal != 0;
+					rangeCheckMax = maxVal != (1<<mBFieldType.Size*8)-1;
+				}
+			}
+
+			if (mAccessFlags.HasFlag(.Write))
+			{
+				for (int pass < 2) 
+				{
+					if (!rangeCheckMin && !rangeCheckMax)
+					{
+						if (pass == 0)
+						{
+							str.AppendF($"\t[Inline]\n\tset{(fieldInfo.Owner.IsStruct ? " mut" : "")}\n\t{{\n");
+						}
+						else
+							break;
+					}
+					else
+					{
+						str.AppendF($"\t[Inline, {((pass == 0) ? "Checked" : "Unchecked")}]\n\tset{(fieldInfo.Owner.IsStruct ? " mut" : "")}\n\t{{\n");
+						if ((pass == 0) && (rangeCheckMin) && (rangeCheckMax))
+							str.AppendF($"\t\tRuntime.Assert((value >= {minVal}) && (value <= {maxVal}));\n");
+						else if ((pass == 0) && (rangeCheckMin))
+							str.AppendF($"\t\tRuntime.Assert(value >= {minVal});\n");
+						else if ((pass == 0) && (rangeCheckMax))
+							str.AppendF($"\t\tRuntime.Assert(value <= {maxVal});\n");
+					}
+
+					if (mBFieldType == typeof(bool))
+						str.AppendF($"\t\t{fieldInfo.Name} = ({fieldInfo.Name} & ({uTypeStr})~0x{mask:X}) | (value ? 0x{mask:X} : 0);\n");
+					else
+						str.AppendF($"\t\t{fieldInfo.Name} = ({fieldInfo.Name} & ({uTypeStr})~0x{mask:X}) | ((({uTypeStr})value << {mBitPos}) & ({uTypeStr})0x{mask:X});\n");
+
+					str.Append("\t}\n");
+				}
+			}
+
+			str.Append("}\n");
+
+			Compiler.EmitTypeBody(fieldInfo.Owner, str);
+
+			if (!isRev)
+				mBitPos += bitCount;
+			mFieldIdx = (.)fieldInfo.FieldIdx;
+		}
+	}
+
+	[AttributeUsage(.Field | .StaticField)]
+	struct BitfieldAttribute<TField> : BitfieldAttribute
+	{
+		int GetBitCount()
+		{
+			int val = typeof(TField).BitSize;
+			return val;
+		}
+
+		BitSpec FixSpec(BitSpec spec)
+		{
+			switch (spec)
+			{
+			case .Auto:
+				return .Bits(typeof(TField).BitSize);
+			case .AutoRev():
+				return .BitsRev(typeof(TField).BitSize);
+			case .AutoAt(let pos):
+				return .BitsAt(typeof(TField).BitSize, pos);
+			default:
+				return spec;
+			}
+		}
+
+		public this(ProtectionKind protection, String name, AccessFlags accessFlags = .Read | .Write) : base(protection, FixSpec(.Auto), name, accessFlags)
+		{
+			/*if (Compiler.IsBuilding)
+				Debug.WriteLine($"typeof.BitSize:{typeof(TField).BitSize} mBitCount:{mBitCount}"); //*/
+			mBFieldType = typeof(TField);
+		}
+
+		public this(ProtectionKind protection, BitSpec bitSpec, String name, AccessFlags accessFlags = .Read | .Write) : base(protection, FixSpec(bitSpec), name, accessFlags)
+		{
+			mBFieldType = typeof(TField);
+		}
+	}
+}
diff --git a/BeefLibs/corlib/src/Collections/List.bf b/BeefLibs/corlib/src/Collections/List.bf
index c440f74b..70a4e7fb 100644
--- a/BeefLibs/corlib/src/Collections/List.bf
+++ b/BeefLibs/corlib/src/Collections/List.bf
@@ -216,12 +216,7 @@ namespace System.Collections
 			[Checked]
 			get
 			{
-				int idx;
-				switch (index)
-				{
-				case .FromFront(let offset): idx = offset;
-				case .FromEnd(let offset): idx = mSize - offset;
-				}
+				int idx = index.Get(mSize);
 				Runtime.Assert((uint)idx < (uint)mSize);
 				return ref mItems[idx];
 			}
@@ -229,24 +224,13 @@ namespace System.Collections
 			[Unchecked, Inline]
 			get
 			{
-				int idx;
-				switch (index)
-				{
-				case .FromFront(let offset): idx = offset;
-				case .FromEnd(let offset): idx = mSize - offset;
-				}
-				return ref mItems[idx];
+				return ref mItems[index.Get(mSize)];
 			}
 
 			[Checked]
 			set
 			{
-				int idx;
-				switch (index)
-				{
-				case .FromFront(let offset): idx = offset;
-				case .FromEnd(let offset): idx = mSize - offset;
-				}
+				int idx = index.Get(mSize);
 				Runtime.Assert((uint)idx < (uint)mSize);
 				mItems[idx] = value;
 #if VERSION_LIST
@@ -257,13 +241,7 @@ namespace System.Collections
 			[Unchecked, Inline]
 			set
 			{
-				int idx;
-				switch (index)
-				{
-				case .FromFront(let offset): idx = offset;
-				case .FromEnd(let offset): idx = mSize - offset;
-				}
-				mItems[idx] = value;
+				mItems[index.Get(mSize)] = value;
 #if VERSION_LIST
 				mVersion++;
 #endif
diff --git a/BeefLibs/corlib/src/Range.bf b/BeefLibs/corlib/src/Range.bf
index dae1f2a1..7614d3c6 100644
--- a/BeefLibs/corlib/src/Range.bf
+++ b/BeefLibs/corlib/src/Range.bf
@@ -24,6 +24,16 @@ namespace System
 				offset.ToString(strBuffer);
 			}
 		}
+
+		[Inline]
+		public int Get(int size)
+		{
+			switch (this)
+			{
+			case .FromFront(let offset): return offset;
+			case .FromEnd(let offset): return size - offset;
+			}
+		}
 	}
 
 	struct Range : RangeExpression, IEnumerable<int>
@@ -310,6 +320,14 @@ namespace System
 				strBuffer.Append("..<");
 			mEnd.ToString(strBuffer);
 		}
+
+		public int GetLength(int size)
+		{
+			int length = mEnd.Get(size) - mStart.Get(size);
+			if (mIsClosed)
+				length++;
+			return length;
+		}
 	}
 
 	struct ClosedRange : RangeExpression, IEnumerable<int>
diff --git a/BeefySysLib/BeefySysLib.vcxproj b/BeefySysLib/BeefySysLib.vcxproj
index b84cb83f..5a38ca1f 100644
--- a/BeefySysLib/BeefySysLib.vcxproj
+++ b/BeefySysLib/BeefySysLib.vcxproj
@@ -2153,6 +2153,7 @@ copy /y "$(OutDir)$(TargetName).lib" "$(SolutionDir)\BeefLibs\Beefy2D\dist\"</Co
     <ClInclude Include="util\Array.h" />
     <ClInclude Include="util\BeefPerf.h" />
     <ClInclude Include="util\BinaryHeap.h" />
+    <ClInclude Include="util\BitSet.h" />
     <ClInclude Include="util\BSpline.h" />
     <ClInclude Include="util\BumpAllocator.h" />
     <ClInclude Include="util\CatmullRom.h" />
diff --git a/BeefySysLib/BeefySysLib.vcxproj.filters b/BeefySysLib/BeefySysLib.vcxproj.filters
index 016806a0..c82a47af 100644
--- a/BeefySysLib/BeefySysLib.vcxproj.filters
+++ b/BeefySysLib/BeefySysLib.vcxproj.filters
@@ -1105,6 +1105,9 @@
     <ClInclude Include="util\Compress.h">
       <Filter>src\util</Filter>
     </ClInclude>
+    <ClInclude Include="util\BitSet.h">
+      <Filter>src\util</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <CustomBuild Include="third_party\libffi\i686-pc-cygwin\src\x86\win32.asm">
diff --git a/BeefySysLib/util/BitSet.h b/BeefySysLib/util/BitSet.h
new file mode 100644
index 00000000..87160ec5
--- /dev/null
+++ b/BeefySysLib/util/BitSet.h
@@ -0,0 +1,61 @@
+#pragma once
+
+#include "BFPlatform.h"
+
+NS_BF_BEGIN;
+
+#define BF_BITSET_ELEM_SIZE (sizeof(uintptr)*8)
+
+class BitSet
+{
+public:
+	uintptr* mBits;
+	int mNumInts;
+
+public:
+	BitSet()
+	{
+		mNumInts = 0;
+		mBits = NULL;
+	}
+
+	BitSet(int numBits)
+	{
+		mNumInts = 0;
+		mBits = NULL;
+		this->Resize(numBits);
+	}
+
+	~BitSet()
+	{
+		delete this->mBits;
+	}
+
+	void Resize(int numBits)
+	{
+		int numInts = (numBits + BF_BITSET_ELEM_SIZE - 1) / BF_BITSET_ELEM_SIZE;
+		if (numInts == mNumInts)
+			return;
+		this->mNumInts = numInts;
+		delete this->mBits;
+		this->mBits = new uintptr[numInts];
+		memset(this->mBits, 0, numInts * sizeof(uintptr));
+	}
+
+	bool IsSet(int idx)
+	{
+		return (this->mBits[idx / BF_BITSET_ELEM_SIZE] & ((uintptr)1 << (idx % BF_BITSET_ELEM_SIZE))) != 0;
+	}
+	
+	void Set(int idx)
+	{
+		this->mBits[idx / BF_BITSET_ELEM_SIZE] |= ((uintptr)1 << (idx % BF_BITSET_ELEM_SIZE));
+	}
+
+	void Clear(int idx)
+	{
+		this->mBits[idx / BF_BITSET_ELEM_SIZE] &= ~((uintptr)1 << (idx % BF_BITSET_ELEM_SIZE));
+	}
+};
+
+NS_BF_END;
\ No newline at end of file
diff --git a/IDEHelper/Tests/src/Bitfields.bf b/IDEHelper/Tests/src/Bitfields.bf
new file mode 100644
index 00000000..c2d10121
--- /dev/null
+++ b/IDEHelper/Tests/src/Bitfields.bf
@@ -0,0 +1,50 @@
+using System;
+namespace Tests
+{
+	class Bitfields
+	{
+		enum EnumA
+		{
+			A = -64,
+			B = 12,
+			C = 63
+		}
+
+		struct StructA
+		{
+			[Bitfield<uint8>(.Public, "A")]
+			[Bitfield<uint8>(.Public, .Bits(3), "B")]
+			[Bitfield<EnumA>(.Public, "C")]
+			[Bitfield(.Public, .ValueRange(0..<12), "D")]
+			public int32 mVal;
+
+			[Bitfield<uint8>(.Public, .AutoRev, "E")]
+			[Bitfield<uint8>(.Public, .BitsRev(8), "F")]
+			[Bitfield<uint8>(.Public, .ValueRangeRev(0..<256), "G")]
+			[Bitfield<uint8>(.Public, .BitsAt(8, 0), "H")]
+			public int32 mVal2;
+		}
+
+		[Test]
+		static void TestBasics()
+		{
+			Test.Assert(sizeof(StructA) == 8);
+			StructA sa = .();
+			sa.A = 0x12;
+			sa.B = 7;
+			sa.C = .C;
+			sa.D = 9;
+			sa.E = 0x22;
+			sa.F = 0x33;
+			sa.G = 0x44;
+			sa.H = 0x55;
+			Test.Assert(sa.A == 0x12);
+			Test.Assert(sa.B == 7);
+			Test.Assert(sa.C == .C);
+			Test.Assert(sa.D == 9);
+
+			Test.Assert(sa.mVal == 0x0025FF12);
+			Test.Assert(sa.mVal2 == 0x22334455);
+		}
+	}
+}
\ No newline at end of file