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using System;
namespace ChocolArm64.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.HighestBitSet32((~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;
}
}
}
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