feat(core): add CHIP-8 disassembler
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dualfroz committed
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using System.Collections.Generic;
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using System.Globalization;
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using System.Text;
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namespace Chip8.Core;
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public readonly struct DecodedInstruction
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{
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public DecodedInstruction(ushort address, ushort opcode, ushort? extraWord, int byteLength, string mnemonic)
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{
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this.address = address;
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this.opcode = opcode;
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this.extraWord = extraWord;
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this.byteLength = byteLength;
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this.mnemonic = mnemonic;
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}
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public ushort address { get; }
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public ushort opcode { get; }
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public ushort? extraWord { get; }
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public int byteLength { get; }
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public string mnemonic { get; }
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public override string ToString()
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{
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string bytes = extraWord.HasValue
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? opcode.ToString("X4", CultureInfo.InvariantCulture) + " " + extraWord.Value.ToString("X4", CultureInfo.InvariantCulture)
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: opcode.ToString("X4", CultureInfo.InvariantCulture);
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return "0x" + address.ToString("X4", CultureInfo.InvariantCulture) + ": " + bytes.PadRight(9) + " " + mnemonic;
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}
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}
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public static class Disassembler
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{
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public static bool isLongLoad(ushort opcode) => opcode == 0xF000;
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public static string describe(ushort opcode, ushort extraWord = 0)
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{
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int x = (opcode & 0x0F00) >> 8;
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int y = (opcode & 0x00F0) >> 4;
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int n = opcode & 0x000F;
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int nn = opcode & 0x00FF;
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int nnn = opcode & 0x0FFF;
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return (opcode & 0xF000) switch
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{
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0x0000 => describeSystem(opcode, n, nnn),
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0x1000 => "JP 0x" + hex3(nnn),
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0x2000 => "CALL 0x" + hex3(nnn),
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0x3000 => "SE V" + hex1(x) + ", 0x" + hex2(nn),
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0x4000 => "SNE V" + hex1(x) + ", 0x" + hex2(nn),
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0x5000 => describeSkipRegister(opcode, x, y, n),
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0x6000 => "LD V" + hex1(x) + ", 0x" + hex2(nn),
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0x7000 => "ADD V" + hex1(x) + ", 0x" + hex2(nn),
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0x8000 => describeArithmetic(opcode, x, y, n),
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0x9000 => n == 0 ? "SNE V" + hex1(x) + ", V" + hex1(y) : dataWord(opcode),
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0xA000 => "LD I, 0x" + hex3(nnn),
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0xB000 => "JP V0, 0x" + hex3(nnn),
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0xC000 => "RND V" + hex1(x) + ", 0x" + hex2(nn),
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0xD000 => "DRW V" + hex1(x) + ", V" + hex1(y) + ", " + n,
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0xE000 => describeKey(opcode, x, nn),
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0xF000 => describeMisc(opcode, x, nn, extraWord),
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_ => dataWord(opcode),
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};
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}
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public static IReadOnlyList<DecodedInstruction> disassemble(byte[] program, ushort baseAddress = 0x200)
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{
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var lines = new List<DecodedInstruction>();
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int offset = 0;
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while (offset + 1 < program.Length)
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{
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ushort address = (ushort)(baseAddress + offset);
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ushort opcode = (ushort)((program[offset] << 8) | program[offset + 1]);
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if (isLongLoad(opcode) && offset + 3 < program.Length)
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{
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ushort extraWord = (ushort)((program[offset + 2] << 8) | program[offset + 3]);
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lines.Add(new DecodedInstruction(address, opcode, extraWord, 4, describe(opcode, extraWord)));
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offset += 4;
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}
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else
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{
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lines.Add(new DecodedInstruction(address, opcode, null, 2, describe(opcode)));
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offset += 2;
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}
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}
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return lines;
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}
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public static string render(byte[] program, ushort baseAddress = 0x200)
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{
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var builder = new StringBuilder();
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foreach (var line in disassemble(program, baseAddress))
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{
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builder.Append(line).Append('\n');
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}
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return builder.ToString();
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}
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static string describeSystem(ushort opcode, int n, int nnn)
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{
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if ((opcode & 0xFFF0) == 0x00C0)
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{
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return "SCD " + n;
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}
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if ((opcode & 0xFFF0) == 0x00D0)
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{
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return "SCU " + n;
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}
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return opcode switch
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{
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0x00E0 => "CLS",
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0x00EE => "RET",
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0x00FB => "SCR",
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0x00FC => "SCL",
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0x00FD => "EXIT",
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0x00FE => "LORES",
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0x00FF => "HIRES",
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_ => "SYS 0x" + hex3(nnn),
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};
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}
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static string describeSkipRegister(ushort opcode, int x, int y, int n) => n switch
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{
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0x0 => "SE V" + hex1(x) + ", V" + hex1(y),
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0x2 => "SAVE V" + hex1(x) + "-V" + hex1(y),
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0x3 => "LOAD V" + hex1(x) + "-V" + hex1(y),
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_ => dataWord(opcode),
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};
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static string describeArithmetic(ushort opcode, int x, int y, int n) => n switch
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{
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0x0 => "LD V" + hex1(x) + ", V" + hex1(y),
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0x1 => "OR V" + hex1(x) + ", V" + hex1(y),
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0x2 => "AND V" + hex1(x) + ", V" + hex1(y),
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0x3 => "XOR V" + hex1(x) + ", V" + hex1(y),
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0x4 => "ADD V" + hex1(x) + ", V" + hex1(y),
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0x5 => "SUB V" + hex1(x) + ", V" + hex1(y),
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0x6 => "SHR V" + hex1(x),
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0x7 => "SUBN V" + hex1(x) + ", V" + hex1(y),
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0xE => "SHL V" + hex1(x),
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_ => dataWord(opcode),
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};
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static string describeKey(ushort opcode, int x, int nn) => nn switch
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{
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0x9E => "SKP V" + hex1(x),
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0xA1 => "SKNP V" + hex1(x),
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_ => dataWord(opcode),
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};
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static string describeMisc(ushort opcode, int x, int nn, ushort extraWord)
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{
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if (opcode == 0xF000)
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{
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return "LD I, 0x" + extraWord.ToString("X4", CultureInfo.InvariantCulture);
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}
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if ((opcode & 0xF0FF) == 0xF001)
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{
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return "PLANE " + x;
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}
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if (opcode == 0xF002)
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{
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return "AUDIO";
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}
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return nn switch
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{
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0x07 => "LD V" + hex1(x) + ", DT",
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0x0A => "LD V" + hex1(x) + ", K",
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0x15 => "LD DT, V" + hex1(x),
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0x18 => "LD ST, V" + hex1(x),
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0x1E => "ADD I, V" + hex1(x),
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0x29 => "LD F, V" + hex1(x),
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0x30 => "LD HF, V" + hex1(x),
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0x33 => "LD B, V" + hex1(x),
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0x3A => "PITCH V" + hex1(x),
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0x55 => "LD [I], V" + hex1(x),
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0x65 => "LD V" + hex1(x) + ", [I]",
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0x75 => "LD R, V" + hex1(x),
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0x85 => "LD V" + hex1(x) + ", R",
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_ => dataWord(opcode),
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};
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}
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static string dataWord(ushort opcode) => "DW 0x" + opcode.ToString("X4", CultureInfo.InvariantCulture);
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static string hex1(int value) => value.ToString("X1", CultureInfo.InvariantCulture);
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static string hex2(int value) => value.ToString("X2", CultureInfo.InvariantCulture);
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static string hex3(int value) => value.ToString("X3", CultureInfo.InvariantCulture);
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}
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