1 files changed, 113 insertions, 0 deletions
diff --git a/ARMeilleure/Decoders/DecoderHelper.cs b/ARMeilleure/Decoders/DecoderHelper.cs
new file mode 100644
index 00000000..3cbd4912
--- /dev/null
+++ b/ARMeilleure/Decoders/DecoderHelper.cs
@@ -0,0 +1,113 @@
+using ARMeilleure.Common;
+using System;
+
+namespace ARMeilleure.Decoders
+{
+    static class DecoderHelper
+    {
+        public struct BitMask
+        {
+            public long WMask;
+            public long TMask;
+            public int  Pos;
+            public int  Shift;
+            public bool IsUndefined;
+
+            public static BitMask Invalid => new BitMask { IsUndefined = true };
+        }
+
+        public static BitMask DecodeBitMask(int opCode, bool immediate)
+        {
+            int immS = (opCode >> 10) & 0x3f;
+            int immR = (opCode >> 16) & 0x3f;
+
+            int n  = (opCode >> 22) & 1;
+            int sf = (opCode >> 31) & 1;
+
+            int length = BitUtils.HighestBitSet((~immS & 0x3f) | (n << 6));
+
+            if (length < 1 || (sf == 0 && n != 0))
+            {
+                return BitMask.Invalid;
+            }
+
+            int size = 1 << length;
+
+            int levels = size - 1;
+
+            int s = immS & levels;
+            int r = immR & levels;
+
+            if (immediate && s == levels)
+            {
+                return BitMask.Invalid;
+            }
+
+            long wMask = BitUtils.FillWithOnes(s + 1);
+            long tMask = BitUtils.FillWithOnes(((s - r) & levels) + 1);
+
+            if (r > 0)
+            {
+                wMask  = BitUtils.RotateRight(wMask, r, size);
+                wMask &= BitUtils.FillWithOnes(size);
+            }
+
+            return new BitMask()
+            {
+                WMask = BitUtils.Replicate(wMask, size),
+                TMask = BitUtils.Replicate(tMask, size),
+
+                Pos   = immS,
+                Shift = immR
+            };
+        }
+
+        public static long DecodeImm8Float(long imm, int size)
+        {
+            int e = 0, f = 0;
+
+            switch (size)
+            {
+                case 0: e =  8; f = 23; break;
+                case 1: e = 11; f = 52; break;
+
+                default: throw new ArgumentOutOfRangeException(nameof(size));
+            }
+
+            long value = (imm & 0x3f) << f - 4;
+
+            long eBit = (imm >> 6) & 1;
+            long sBit = (imm >> 7) & 1;
+
+            if (eBit != 0)
+            {
+                value |= (1L << e - 3) - 1 << f + 2;
+            }
+
+            value |= (eBit ^ 1) << f + e - 1;
+            value |=  sBit      << f + e;
+
+            return value;
+        }
+
+        public static long DecodeImm24_2(int opCode)
+        {
+            return ((long)opCode << 40) >> 38;
+        }
+
+        public static long DecodeImm26_2(int opCode)
+        {
+            return ((long)opCode << 38) >> 36;
+        }
+
+        public static long DecodeImmS19_2(int opCode)
+        {
+            return (((long)opCode << 40) >> 43) & ~3;
+        }
+
+        public static long DecodeImmS14_2(int opCode)
+        {
+            return (((long)opCode << 45) >> 48) & ~3;
+        }
+    }
+}
+\ No newline at end of file