add LLM-gened disas

1 files changed, 190 insertions, 0 deletions

diff --git a/nandgame/assembler/disas.cpp b/nandgame/assembler/disas.cpp
new file mode 100644
index 0000000..8f6ff3b
--- /dev/null
+++ b/nandgame/assembler/disas.cpp
@@ -0,0 +1,190 @@
+// LLM converted. Here be dragons.
+
+#include "disas.h"
+
+#include <string>
+#include <vector>
+#include <sstream>
+#include <iomanip>
+
+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) {
+    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();
+}