1 files changed, 173 insertions, 0 deletions
diff --git a/ARMeilleure/CodeGen/Arm64/CodeGenCommon.cs b/ARMeilleure/CodeGen/Arm64/CodeGenCommon.cs
new file mode 100644
index 00000000..e67d2fdb
--- /dev/null
+++ b/ARMeilleure/CodeGen/Arm64/CodeGenCommon.cs
@@ -0,0 +1,173 @@
+using ARMeilleure.IntermediateRepresentation;
+using System;
+using System.Numerics;
+
+namespace ARMeilleure.CodeGen.Arm64
+{
+    static class CodeGenCommon
+    {
+        public const int TcAddressRegister = 8;
+        public const int ReservedRegister = 17;
+
+        public static bool ConstFitsOnSImm7(int value, int scale)
+        {
+            return (((value >> scale) << 25) >> (25 - scale)) == value;
+        }
+
+        public static bool ConstFitsOnSImm9(int value)
+        {
+            return ((value << 23) >> 23) == value;
+        }
+
+        public static bool ConstFitsOnUImm12(int value)
+        {
+            return (value & 0xfff) == value;
+        }
+
+        public static bool ConstFitsOnUImm12(int value, OperandType type)
+        {
+            int scale = Assembler.GetScaleForType(type);
+            return (((value >> scale) & 0xfff) << scale) == value;
+        }
+
+        public static bool TryEncodeBitMask(Operand operand, out int immN, out int immS, out int immR)
+        {
+            ulong value = operand.Value;
+
+            if (operand.Type == OperandType.I32)
+            {
+                value |= value << 32;
+            }
+
+            return TryEncodeBitMask(value, out immN, out immS, out immR);
+        }
+
+        public static bool TryEncodeBitMask(ulong value, out int immN, out int immS, out int immR)
+        {
+            // Some special values also can't be encoded:
+            // 0 can't be encoded because we need to subtract 1 from onesCount (which would became negative if 0).
+            // A value with all bits set can't be encoded because it is reserved according to the spec, because:
+            // Any value AND all ones will be equal itself, so it's effectively a no-op.
+            // Any value OR all ones will be equal all ones, so one can just use MOV.
+            // Any value XOR all ones will be equal its inverse, so one can just use MVN.
+            if (value == ulong.MaxValue)
+            {
+                immN = 0;
+                immS = 0;
+                immR = 0;
+
+                return false;
+            }
+
+            int bitLength = CountSequence(value);
+
+            if ((value >> bitLength) != 0)
+            {
+                bitLength += CountSequence(value >> bitLength);
+            }
+
+            int bitLengthLog2 = BitOperations.Log2((uint)bitLength);
+            int bitLengthPow2 = 1 << bitLengthLog2;
+
+            if (bitLengthPow2 < bitLength)
+            {
+                bitLengthLog2++;
+                bitLengthPow2 <<= 1;
+            }
+
+            int selectedESize = 64;
+            int repetitions = 1;
+            int onesCount = BitOperations.PopCount(value);
+
+            if (bitLengthPow2 < 64 && (value >> bitLengthPow2) != 0)
+            {
+                for (int eSizeLog2 = bitLengthLog2; eSizeLog2 < 6; eSizeLog2++)
+                {
+                    bool match = true;
+                    int eSize = 1 << eSizeLog2;
+                    ulong mask = (1UL << eSize) - 1;
+                    ulong eValue = value & mask;
+
+                    for (int e = 1; e < 64 / eSize; e++)
+                    {
+                        if (((value >> (e * eSize)) & mask) != eValue)
+                        {
+                            match = false;
+                            break;
+                        }
+                    }
+
+                    if (match)
+                    {
+                        selectedESize = eSize;
+                        repetitions = 64 / eSize;
+                        onesCount = BitOperations.PopCount(eValue);
+                        break;
+                    }
+                }
+            }
+
+            // Find rotation. We have two cases, one where the highest bit is 0
+            // and one where it is 1.
+            // If it's 1, we just need to count the number of 1 bits on the MSB to find the right rotation.
+            // If it's 0, we just need to count the number of 0 bits on the LSB to find the left rotation,
+            // then we can convert it to the right rotation shift by subtracting the value from the element size.
+            int rotation;
+            long vHigh = (long)(value << (64 - selectedESize));
+            if (vHigh < 0)
+            {
+                rotation = BitOperations.LeadingZeroCount(~(ulong)vHigh);
+            }
+            else
+            {
+                rotation = (selectedESize - BitOperations.TrailingZeroCount(value)) & (selectedESize - 1);
+            }
+
+            // Reconstruct value and see if it matches. If not, we can't encode.
+            ulong reconstructed = onesCount == 64 ? ulong.MaxValue : RotateRight((1UL << onesCount) - 1, rotation, selectedESize);
+
+            for (int bit = 32; bit >= selectedESize; bit >>= 1)
+            {
+                reconstructed |= reconstructed << bit;
+            }
+
+            if (reconstructed != value || onesCount == 0)
+            {
+                immN = 0;
+                immS = 0;
+                immR = 0;
+
+                return false;
+            }
+
+            immR = rotation;
+
+            // immN indicates that there are no repetitions.
+            // The MSB of immS indicates the amount of repetitions, and the LSB the number of bits set.
+            if (repetitions == 1)
+            {
+                immN = 1;
+                immS = 0;
+            }
+            else
+            {
+                immN = 0;
+                immS = (0xf80 >> BitOperations.Log2((uint)repetitions)) & 0x3f;
+            }
+
+            immS |= onesCount - 1;
+
+            return true;
+        }
+
+        private static int CountSequence(ulong value)
+        {
+            return BitOperations.TrailingZeroCount(value) + BitOperations.TrailingZeroCount(~value);
+        }
+
+        private static ulong RotateRight(ulong bits, int shift, int size)
+        {
+            return (bits >> shift) | ((bits << (size - shift)) & (size == 64 ? ulong.MaxValue : (1UL << size) - 1));
+        }
+    }
+}
+\ No newline at end of file