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97 lines
3.2 KiB
Odin
97 lines
3.2 KiB
Odin
package rexcode_mos6502
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// =============================================================================
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// INSTRUCTION
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// =============================================================================
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//
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// Up to 3 operands per instruction (only the HuC6280 block-transfer ops
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// actually use all three; the rest top out at two).
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Instruction_Flags :: bit_field u8 {
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_: u8 | 8,
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}
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Instruction :: struct #packed {
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ops: [3]Operand `fmt:"v,operand_count"`, // 48 bytes
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mnemonic: Mnemonic, // 2
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operand_count: u8, // 1
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flags: Instruction_Flags, // 1
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length: u8, // 1 (filled by decoder; 1..7)
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_: [3]u8, // 3
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}
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#assert(size_of(Instruction) == 56)
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// =============================================================================
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// Builders (mirror the contract: shape spelled out, comma-separated)
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// =============================================================================
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@(require_results)
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inst_none :: #force_inline proc "contextless" (m: Mnemonic) -> Instruction {
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return Instruction{mnemonic = m, operand_count = 0, length = 1}
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}
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@(require_results)
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inst_a :: #force_inline proc "contextless" (m: Mnemonic) -> Instruction {
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// Explicit accumulator (e.g. `ROL A`). Encodes to 1 byte (opcode only)
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// and counts as 1 operand for the matcher.
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return Instruction{
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mnemonic = m, operand_count = 1, length = 1,
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ops = {op_reg(A), {}, {}},
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}
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}
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@(require_results)
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inst_i :: #force_inline proc "contextless" (m: Mnemonic, imm: i64) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 1, length = 2,
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ops = {op_imm8(imm), {}, {}},
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}
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}
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@(require_results)
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inst_m :: #force_inline proc "contextless" (m: Mnemonic, mm: Memory) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 1, length = 0, // filled by encoder
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ops = {op_mem(mm), {}, {}},
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}
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}
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@(require_results)
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inst_rel :: #force_inline proc "contextless" (m: Mnemonic, label_id: u32) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 1, length = 2,
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ops = {op_label(label_id, 1), {}, {}},
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}
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}
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// BBR/BBS: zero-page byte + relative branch (3-byte encoding).
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@(require_results)
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inst_zp_rel :: #force_inline proc "contextless" (m: Mnemonic, zp: u8, label_id: u32) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 2, length = 3,
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ops = {op_zp(zp), op_label(label_id, 1), {}},
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}
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}
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// HuC6280 TST # imm, addr (3 or 4 bytes depending on addressing mode).
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@(require_results)
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inst_tst :: #force_inline proc "contextless" (m: Mnemonic, imm: i64, mm: Memory) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 2, length = 0,
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ops = {op_imm8(imm), op_mem(mm), {}},
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}
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}
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// HuC6280 block transfer: src, dst, length (7-byte encoding).
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@(require_results)
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inst_block :: #force_inline proc "contextless" (m: Mnemonic, src, dst, length_val: u16) -> Instruction {
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return Instruction{
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mnemonic = m, operand_count = 3, length = 7,
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ops = {
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Operand{immediate = i64(src), kind = .IMMEDIATE, size = 2},
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Operand{immediate = i64(dst), kind = .IMMEDIATE, size = 2},
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Operand{immediate = i64(length_val), kind = .IMMEDIATE, size = 2},
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},
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}
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}
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