1 files changed, 212 insertions, 0 deletions
diff --git a/nandgame/cpp/disas.cpp b/nandgame/cpp/disas.cpp
new file mode 100644
index 0000000..f6c3cf7
--- /dev/null
+++ b/nandgame/cpp/disas.cpp
@@ -0,0 +1,212 @@
+// LLM converted. Here be dragons.
+
+#include "disas.h"
+
+#include <iomanip>
+#include <sstream>
+#include <string>
+#include <vector>
+
+static const std::string ZERO = "#0";
+static const std::string DEST_NONE = "_";
+static const std::string JUMP_NONE = "";
+
+static const std::vector<std::string> JUMPS_IF_NZERO = {"jgt", "jlt", "jne",
+                                                        "jmp"};
+static const std::vector<std::string> JUMPS_IF_ZERO = {"jge", "jle", "jeq",
+                                                       "jmp"};
+
+struct Decoded {
+  std::string mnemonic;
+  std::string dest;
+  std::string op1;
+  std::string op2;
+  std::string jumpdest;
+};
+
+static bool in_list(const std::string &s, const std::vector<std::string> &v) {
+  for (const auto &x : v) {
+    if (x == s)
+      return true;
+  }
+  return false;
+}
+
+static std::string decode_jump(uint16_t ins) {
+  if ((ins & 0x7) == 0) {
+    return JUMP_NONE;
+  }
+
+  if ((ins & 0x7) == 0x7) {
+    return "jmp";
+  }
+
+  bool jl = (ins & (1 << 2)) != 0;
+  bool je = (ins & (1 << 1)) != 0;
+  bool jg = (ins & (1 << 0)) != 0;
+
+  if (jl && je) {
+    return "jle";
+  }
+  if (jl && jg) {
+    return "jne";
+  }
+  if (je && jg) {
+    return "jge";
+  }
+
+  if (jl)
+    return "jlt";
+  if (je)
+    return "jeq";
+  if (jg)
+    return "jgt";
+
+  return "<unknown>";
+}
+
+static std::pair<std::string, bool> decode_ins(uint16_t ins) {
+  int opcode = (ins >> 8) & 0x03;
+  bool ar_n_log = (ins & (1 << 10)) != 0;
+  opcode |= (ar_n_log ? 1 : 0) << 2;
+
+  switch (opcode) {
+  case 0b000:
+    return {"and", true};
+  case 0b001:
+    return {"or", true};
+  case 0b010:
+    return {"xor", true};
+  case 0b011:
+    return {"not", false};
+  case 0b100:
+    return {"add", true};
+  case 0b101:
+    return {"inc", false};
+  case 0b110:
+    return {"sub", true};
+  case 0b111:
+    return {"dec", false};
+  default:
+    return {"<?>", false};
+  }
+}
+
+static std::string decode_arg1(uint16_t ins) {
+  bool use_mem = (ins & (1 << 12)) != 0;
+  bool zx = (ins & (1 << 7)) != 0;
+  bool sw = (ins & (1 << 6)) != 0;
+
+  if (zx)
+    return ZERO;
+  if (!sw)
+    return "D";
+  return use_mem ? "M" : "A";
+}
+
+static std::string decode_arg2(uint16_t ins) {
+  bool use_mem = (ins & (1 << 12)) != 0;
+  bool sw = (ins & (1 << 6)) != 0;
+
+  if (sw)
+    return "D";
+  return use_mem ? "M" : "A";
+}
+
+static std::string decode_dest(uint16_t ins) {
+  bool dA = (ins & (1 << 5)) != 0;
+  bool dD = (ins & (1 << 4)) != 0;
+  bool dM = (ins & (1 << 3)) != 0;
+
+  std::string dest;
+  if (dA)
+    dest += "A";
+  if (dD)
+    dest += "D";
+  if (dM)
+    dest += "M";
+
+  return dest.empty() ? DEST_NONE : dest;
+}
+
+static Decoded decode_instruction(uint16_t ins) {
+  if ((ins & 0x8000) == 0) {
+    return {"mov", "A", "#" + std::to_string(ins), "", ""};
+  } else {
+    auto [mnemonic, two_op] = decode_ins(ins);
+    std::string dest = decode_dest(ins);
+    std::string op1 = decode_arg1(ins);
+    std::string op2 = two_op ? decode_arg2(ins) : "";
+    std::string jumpdst = decode_jump(ins);
+    return {mnemonic, dest, op1, op2, jumpdst};
+  }
+}
+
+static Decoded fixup_ins(uint16_t ins) {
+  Decoded d = decode_instruction(ins);
+  std::string &mnemonic = d.mnemonic;
+  std::string &dest = d.dest;
+  std::string &op1 = d.op1;
+  std::string &op2 = d.op2;
+  std::string &jumpdest = d.jumpdest;
+
+  if (op1 == ZERO) {
+    if (mnemonic == "sub") {
+      return {"neg", dest, op2, "", jumpdest};
+    }
+
+    if (mnemonic == "and") {
+      if (dest == DEST_NONE) {
+        if (in_list(jumpdest, JUMPS_IF_ZERO)) {
+          return {"jmp", "", "", "", ""};
+        } else {
+          return {"nop", "", "", "", ""};
+        }
+      } else {
+        std::string newjmp = in_list(jumpdest, JUMPS_IF_ZERO) ? "jmp" : "";
+        return {"mov", dest, ZERO, "", newjmp};
+      }
+    }
+
+    if (mnemonic == "add" || mnemonic == "or" || mnemonic == "xor") {
+      if (dest == DEST_NONE && jumpdest == JUMP_NONE) {
+        return {"nop", "", "", "", ""};
+      } else {
+        return {"mov", dest, op2, "", jumpdest};
+      }
+    }
+
+    if (mnemonic == "not") {
+      if (dest == DEST_NONE) {
+        if (jumpdest == "jeq" || jumpdest == "jgt" || jumpdest == "jge" ||
+            jumpdest == JUMP_NONE) {
+          return {"nop", "", "", "", ""};
+        } else {
+          return {"jmp", "", "", "", ""};
+        }
+      }
+    }
+  }
+
+  return d;
+}
+
+std::string print_decoded(uint16_t ins, bool simplify) {
+  // illegal instruction
+  if ((ins & 0xC000) == 0x8000)
+    return "halt";
+
+  Decoded d = simplify ? fixup_ins(ins) : decode_instruction(ins);
+
+  std::string jumpdest_str = d.jumpdest.empty() ? "" : "." + d.jumpdest;
+  std::string opcode_str = d.mnemonic + jumpdest_str;
+  std::string dest_str = d.dest.empty() ? std::string(7, ' ') : d.dest + ", ";
+  std::string op2_str = d.op2.empty() ? "" : ", ";
+  std::string op1_str = d.op1 + op2_str;
+
+  std::ostringstream oss;
+  oss << std::left << std::setw(9) << opcode_str << std::setw(6) << dest_str
+      << std::setw(4) << op1_str << d.op2;
+
+  return oss.str();
+}