feat(analysis): add CHIP-8 instruction decoder
This commit is contained in:
dualfroz committed
1 parent
a3e9a99c27
commit
3894bbc1e8
1 file changed
+207
@@ -0,0 +1,207 @@
|
||||
using System.Collections.Generic;
|
||||
using Chip8.Core;
|
||||
|
||||
namespace Chip8.Analysis;
|
||||
|
||||
public static class InstructionDecoder
|
||||
{
|
||||
public const ushort defaultBaseAddress = 0x200;
|
||||
|
||||
public static InstructionInfo? decodeAt(byte[] program, ushort address, ushort baseAddress = defaultBaseAddress)
|
||||
{
|
||||
int offset = address - baseAddress;
|
||||
if (offset < 0 || offset + 1 >= program.Length)
|
||||
{
|
||||
return null;
|
||||
}
|
||||
|
||||
ushort opcode = (ushort)((program[offset] << 8) | program[offset + 1]);
|
||||
|
||||
if (opcode == 0xF000 && offset + 3 < program.Length)
|
||||
{
|
||||
ushort extraWord = (ushort)((program[offset + 2] << 8) | program[offset + 3]);
|
||||
return decode(address, opcode, extraWord, 4);
|
||||
}
|
||||
|
||||
return decode(address, opcode, null, 2);
|
||||
}
|
||||
|
||||
public static int byteLengthAt(byte[] program, ushort address, ushort baseAddress = defaultBaseAddress)
|
||||
{
|
||||
int offset = address - baseAddress;
|
||||
if (offset < 0 || offset + 1 >= program.Length)
|
||||
{
|
||||
return 2;
|
||||
}
|
||||
ushort opcode = (ushort)((program[offset] << 8) | program[offset + 1]);
|
||||
return opcode == 0xF000 && offset + 3 < program.Length ? 4 : 2;
|
||||
}
|
||||
|
||||
public static InstructionInfo decode(ushort address, ushort opcode, ushort? extraWord, int byteLength)
|
||||
{
|
||||
var (kind, category, flow) = classify(opcode);
|
||||
string mnemonic = Disassembler.describe(opcode, extraWord ?? 0);
|
||||
return new InstructionInfo(address, opcode, extraWord, byteLength, kind, category, flow, mnemonic);
|
||||
}
|
||||
|
||||
public static IReadOnlyList<InstructionInfo> decodeLinear(byte[] program, ushort baseAddress = defaultBaseAddress)
|
||||
{
|
||||
var instructions = new List<InstructionInfo>();
|
||||
int offset = 0;
|
||||
while (offset + 1 < program.Length)
|
||||
{
|
||||
ushort address = (ushort)(baseAddress + offset);
|
||||
var info = decodeAt(program, address, baseAddress);
|
||||
if (info is null)
|
||||
{
|
||||
break;
|
||||
}
|
||||
instructions.Add(info);
|
||||
offset += info.byteLength;
|
||||
}
|
||||
return instructions;
|
||||
}
|
||||
|
||||
static (InstructionKind, InstructionCategory, FlowEffect) classify(ushort opcode)
|
||||
{
|
||||
int high = opcode & 0xF000;
|
||||
int x = (opcode & 0x0F00) >> 8;
|
||||
int y = (opcode & 0x00F0) >> 4;
|
||||
int n = opcode & 0x000F;
|
||||
int nn = opcode & 0x00FF;
|
||||
|
||||
switch (high)
|
||||
{
|
||||
case 0x0000:
|
||||
return classifySystem(opcode, n);
|
||||
|
||||
case 0x1000:
|
||||
return (InstructionKind.Jump, InstructionCategory.Control, FlowEffect.Jump);
|
||||
|
||||
case 0x2000:
|
||||
return (InstructionKind.Call, InstructionCategory.Control, FlowEffect.Call);
|
||||
|
||||
case 0x3000:
|
||||
return (InstructionKind.SkipEqualImmediate, InstructionCategory.Skip, FlowEffect.Branch);
|
||||
|
||||
case 0x4000:
|
||||
return (InstructionKind.SkipNotEqualImmediate, InstructionCategory.Skip, FlowEffect.Branch);
|
||||
|
||||
case 0x5000:
|
||||
return n switch
|
||||
{
|
||||
0x0 => (InstructionKind.SkipEqualRegister, InstructionCategory.Skip, FlowEffect.Branch),
|
||||
0x2 => (InstructionKind.SaveRange, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x3 => (InstructionKind.LoadRange, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
_ => dataWord,
|
||||
};
|
||||
|
||||
case 0x6000:
|
||||
return (InstructionKind.LoadImmediate, InstructionCategory.Arithmetic, FlowEffect.Fallthrough);
|
||||
|
||||
case 0x7000:
|
||||
return (InstructionKind.AddImmediate, InstructionCategory.Arithmetic, FlowEffect.Fallthrough);
|
||||
|
||||
case 0x8000:
|
||||
return classifyArithmetic(n);
|
||||
|
||||
case 0x9000:
|
||||
return n == 0
|
||||
? (InstructionKind.SkipNotEqualRegister, InstructionCategory.Skip, FlowEffect.Branch)
|
||||
: dataWord;
|
||||
|
||||
case 0xA000:
|
||||
return (InstructionKind.LoadIndex, InstructionCategory.Memory, FlowEffect.Fallthrough);
|
||||
|
||||
case 0xB000:
|
||||
return (InstructionKind.JumpWithOffset, InstructionCategory.Control, FlowEffect.IndirectJump);
|
||||
|
||||
case 0xC000:
|
||||
return (InstructionKind.Random, InstructionCategory.Arithmetic, FlowEffect.Fallthrough);
|
||||
|
||||
case 0xD000:
|
||||
return (InstructionKind.Draw, InstructionCategory.Draw, FlowEffect.Fallthrough);
|
||||
|
||||
case 0xE000:
|
||||
return nn switch
|
||||
{
|
||||
0x9E => (InstructionKind.SkipKeyPressed, InstructionCategory.Skip, FlowEffect.Branch),
|
||||
0xA1 => (InstructionKind.SkipKeyReleased, InstructionCategory.Skip, FlowEffect.Branch),
|
||||
_ => dataWord,
|
||||
};
|
||||
|
||||
case 0xF000:
|
||||
return classifyMisc(opcode, nn);
|
||||
}
|
||||
|
||||
return dataWord;
|
||||
}
|
||||
|
||||
static (InstructionKind, InstructionCategory, FlowEffect) classifySystem(ushort opcode, int n)
|
||||
{
|
||||
if ((opcode & 0xFFF0) == 0x00C0)
|
||||
{
|
||||
return (InstructionKind.ScrollDown, InstructionCategory.Draw, FlowEffect.Fallthrough);
|
||||
}
|
||||
if ((opcode & 0xFFF0) == 0x00D0)
|
||||
{
|
||||
return (InstructionKind.ScrollUp, InstructionCategory.Draw, FlowEffect.Fallthrough);
|
||||
}
|
||||
|
||||
return opcode switch
|
||||
{
|
||||
0x00E0 => (InstructionKind.ClearScreen, InstructionCategory.Draw, FlowEffect.Fallthrough),
|
||||
0x00EE => (InstructionKind.Return, InstructionCategory.Control, FlowEffect.Return),
|
||||
0x00FB => (InstructionKind.ScrollRight, InstructionCategory.Draw, FlowEffect.Fallthrough),
|
||||
0x00FC => (InstructionKind.ScrollLeft, InstructionCategory.Draw, FlowEffect.Fallthrough),
|
||||
0x00FD => (InstructionKind.Exit, InstructionCategory.Control, FlowEffect.Terminate),
|
||||
0x00FE => (InstructionKind.LowRes, InstructionCategory.Draw, FlowEffect.Fallthrough),
|
||||
0x00FF => (InstructionKind.HiRes, InstructionCategory.Draw, FlowEffect.Fallthrough),
|
||||
_ => (InstructionKind.System, InstructionCategory.Control, FlowEffect.Fallthrough),
|
||||
};
|
||||
}
|
||||
|
||||
static (InstructionKind, InstructionCategory, FlowEffect) classifyArithmetic(int n) => n switch
|
||||
{
|
||||
0x0 or 0x1 or 0x2 or 0x3 or 0x4 or 0x5 or 0x6 or 0x7 or 0xE =>
|
||||
(InstructionKind.Arithmetic, InstructionCategory.Arithmetic, FlowEffect.Fallthrough),
|
||||
_ => dataWord,
|
||||
};
|
||||
|
||||
static (InstructionKind, InstructionCategory, FlowEffect) classifyMisc(ushort opcode, int nn)
|
||||
{
|
||||
if (opcode == 0xF000)
|
||||
{
|
||||
return (InstructionKind.LoadLong, InstructionCategory.Memory, FlowEffect.Fallthrough);
|
||||
}
|
||||
if ((opcode & 0xF0FF) == 0xF001)
|
||||
{
|
||||
return (InstructionKind.Plane, InstructionCategory.Draw, FlowEffect.Fallthrough);
|
||||
}
|
||||
if (opcode == 0xF002)
|
||||
{
|
||||
return (InstructionKind.Audio, InstructionCategory.Sound, FlowEffect.Fallthrough);
|
||||
}
|
||||
|
||||
return nn switch
|
||||
{
|
||||
0x07 => (InstructionKind.LoadDelay, InstructionCategory.Timer, FlowEffect.Fallthrough),
|
||||
0x0A => (InstructionKind.WaitKey, InstructionCategory.Io, FlowEffect.Fallthrough),
|
||||
0x15 => (InstructionKind.SetDelay, InstructionCategory.Timer, FlowEffect.Fallthrough),
|
||||
0x18 => (InstructionKind.SetSound, InstructionCategory.Sound, FlowEffect.Fallthrough),
|
||||
0x1E => (InstructionKind.AddIndex, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x29 => (InstructionKind.LoadFont, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x30 => (InstructionKind.LoadBigFont, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x33 => (InstructionKind.StoreBcd, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x3A => (InstructionKind.Pitch, InstructionCategory.Sound, FlowEffect.Fallthrough),
|
||||
0x55 => (InstructionKind.StoreRegisters, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x65 => (InstructionKind.LoadRegisters, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x75 => (InstructionKind.StoreFlags, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
0x85 => (InstructionKind.LoadFlags, InstructionCategory.Memory, FlowEffect.Fallthrough),
|
||||
_ => dataWord,
|
||||
};
|
||||
}
|
||||
|
||||
static (InstructionKind, InstructionCategory, FlowEffect) dataWord =>
|
||||
(InstructionKind.Data, InstructionCategory.Data, FlowEffect.Fallthrough);
|
||||
}
|
||||
Reference in new issue
Block a user