nesemu/cpu/decoding.c

//
// Created by william on 1/9/24.
//

#include "decoding.h"

#include <assert.h>
#include "log.h"

address decode_operand_addr(AddressingMode addr_mode, bool *page_crossing) {
    CPU *registers = cpu_get_state();
    address operand_addr;

    if (addr_mode == ADDR_MODE_ZERO_PAGE) {
        operand_addr = cpu_get_next_byte();
    } else if (addr_mode == ADDR_MODE_ZERO_PAGE_INDEXED_X) {
        operand_addr = (cpu_get_next_byte() + registers->x) & 0xff;
    } else if (addr_mode == ADDR_MODE_ZERO_PAGE_INDEXED_Y) {
        operand_addr = (cpu_get_next_byte() + registers->y) & 0xff;
    } else if (addr_mode == ADDR_MODE_ABSOLUTE) {
        operand_addr = cpu_get_next_word();
    } else if (addr_mode == ADDR_MODE_ABSOLUTE_INDEXED_X) {
        word addr = cpu_get_next_word();
        word new_addr = addr + registers->x;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        operand_addr = new_addr;
    } else if (addr_mode == ADDR_MODE_ABSOLUTE_INDEXED_Y) {
        word addr = cpu_get_next_word();
        word new_addr = addr + registers->y;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        operand_addr = new_addr;
    } else if (addr_mode == ADDR_MODE_INDIRECT_JUMP) {
        word addr = cpu_get_next_word();
        if ((addr & 0xff) == 0xff) {
            // Error in NES CPU for JMP op
            word result = mem_get_byte(addr);
            result += mem_get_byte(addr & 0xff00) << 8;
            operand_addr = result;
        } else {
            operand_addr = mem_get_word(addr);
        }
    } else if (addr_mode == ADDR_MODE_INDIRECT_X) {
        byte arg_addr = cpu_get_next_byte();

        word addr = mem_get_byte((arg_addr + registers->x) & 0xff);
        addr += mem_get_byte((arg_addr + registers->x + 1) & 0xff) << 8;
        operand_addr = addr;
    } else if (addr_mode == ADDR_MODE_INDIRECT_Y) {
        byte arg_addr = cpu_get_next_byte();
        word addr = mem_get_byte(arg_addr) + (mem_get_byte((arg_addr + 1) & 0xff) << 8);
        word new_addr = addr + registers->y;

        *page_crossing = (addr & 0xff00) != (new_addr & 0xff00);

        operand_addr = new_addr;
    } else {
        assert(false);
    }

    log_trace("Operand address: %#02x, Addressing mode: %s", operand_addr, get_addr_mode_name(addr_mode));
    return operand_addr;
}

Operand decode_operand(AddressingMode addr_mode) {
    Operand operand;

    if (addr_mode == ADDR_MODE_ACCUMULATOR) {
        operand.type = OPERAND_TYPE_ACCUMULATOR;
        operand.value = 0;
        operand.is_page_crossing = false;
    } else if (addr_mode == ADDR_MODE_IMMEDIATE) {
        operand.type = OPERAND_TYPE_IMMEDIATE;
        operand.value = cpu_get_next_byte();
        operand.is_page_crossing = false;
    } else {
        operand.type = OPERAND_TYPE_ADDRESS;
        operand.value = decode_operand_addr(addr_mode, &operand.is_page_crossing);
    }

    log_trace("Operand type: %s, value: %#02x", operand_name(&operand), operand.value);
    return operand;
}

byte read_operand(Operand operand) {
    switch (operand.type) {
        case OPERAND_TYPE_ACCUMULATOR:
            return cpu_get_state()->accumulator;
        case OPERAND_TYPE_IMMEDIATE:
            return (byte) operand.value;
        case OPERAND_TYPE_ADDRESS:
            return mem_get_byte(operand.value);
        default:
            assert(false);
    }
}

char *get_addr_mode_name(AddressingMode addr_mode) {
    switch (addr_mode) {
        case ADDR_MODE_ABSOLUTE:
            return "a";
        case ADDR_MODE_ABSOLUTE_INDEXED_X:
            return "a,x";
        case ADDR_MODE_ABSOLUTE_INDEXED_Y:
            return "a,y";
        case ADDR_MODE_ACCUMULATOR:
            return "A";
        case ADDR_MODE_IMMEDIATE:
            return "#";
        case ADDR_MODE_IMPLICIT:
            return " ";
        case ADDR_MODE_INDIRECT_X:
            return "(d,x)";
        case ADDR_MODE_INDIRECT_Y:
            return "(d,y)";
        case ADDR_MODE_INDIRECT_JUMP:
            return "(a)";
        case ADDR_MODE_RELATIVE:
            return "label";
        case ADDR_MODE_ZERO_PAGE:
            return "d";
        case ADDR_MODE_ZERO_PAGE_INDEXED_X:
            return "d,x";
        case ADDR_MODE_ZERO_PAGE_INDEXED_Y:
            return "d,y";
    }
}

char *operand_name(Operand *operand) {
    switch (operand->type) {
        case OPERAND_TYPE_ACCUMULATOR:
            return "Accumulator";
        case OPERAND_TYPE_IMMEDIATE:
            return "Immediate";
        case OPERAND_TYPE_ADDRESS:
            return "Address";
    }
}

char *get_op_code_name(byte op) {
    switch (op) {
        case 0x00:
            return "BRK";
        case 0x08:
            return "PHP";
        case 0x0b:
        case 0x2b:
            return "ANC";
        case 0x10:
            return "BPL";
        case 0x18:
            return "CLC";
        case 0x20:
            return "JSR";
        case 0x24:
        case 0x2c:
            return "BIT";
        case 0x28:
            return "PLP";
        case 0x30:
            return "BMI";
        case 0x38:
            return "SEC";
        case 0x40:
            return "RTI";
        case 0x48:
            return "PHA";
        case 0x4c:
        case 0x6c:
            return "JMP";
        case 0x50:
            return "BVC";
        case 0x58:
            return "CLI";
        case 0x60:
            return "RTS";
        case 0x68:
            return "PLA";
        case 0x70:
            return "BVS";
        case 0x78:
            return "SEI";
        case 0x84:
        case 0x8c:
        case 0x94:
            return "STY";
        case 0x88:
            return "DEY";
        case 0x90:
            return "BCC";
        case 0x98:
            return "TYA";
        case 0x9c:
            return "SHY";
        case 0xa0:
        case 0xa4:
        case 0xac:
        case 0xb4:
        case 0xbc:
            return "LDY";
        case 0xa8:
            return "TAY";
        case 0xb0:
            return "BCS";
        case 0xb8:
            return "CLV";
        case 0xc0:
        case 0xc4:
        case 0xcc:
            return "CPY";
        case 0xc8:
            return "INY";
        case 0xd0:
            return "BNE";
        case 0xd8:
            return "CLD";
        case 0xe0:
        case 0xe4:
        case 0xec:
            return "CPX";
        case 0xe8:
            return "INX";
        case 0xf0:
            return "BEQ";
        case 0xf8:
            return "SED";

        case 0x01:
        case 0x05:
        case 0x09:
        case 0x0d:
        case 0x11:
        case 0x15:
        case 0x19:
        case 0x1d:
            return "ORA";
        case 0x21:
        case 0x25:
        case 0x29:
        case 0x2d:
        case 0x31:
        case 0x35:
        case 0x39:
        case 0x3d:
            return "AND";
        case 0x41:
        case 0x45:
        case 0x49:
        case 0x4d:
        case 0x51:
        case 0x55:
        case 0x59:
        case 0x5d:
            return "EOR";
        case 0x61:
        case 0x65:
        case 0x69:
        case 0x6d:
        case 0x71:
        case 0x75:
        case 0x79:
        case 0x7d:
            return "ADC";
        case 0x81:
        case 0x85:
        case 0x8d:
        case 0x91:
        case 0x95:
        case 0x99:
        case 0x9d:
            return "STA";
        case 0xa1:
        case 0xa5:
        case 0xa9:
        case 0xad:
        case 0xb1:
        case 0xb5:
        case 0xb9:
        case 0xbd:
            return "LDA";
        case 0xc1:
        case 0xc5:
        case 0xc9:
        case 0xcd:
        case 0xd1:
        case 0xd5:
        case 0xd9:
        case 0xdd:
            return "CMP";
        case 0xe1:
        case 0xe5:
        case 0xe9:
        case 0xed:
        case 0xf1:
        case 0xf5:
        case 0xf9:
        case 0xfd:
            return "SBC";

        case 0x03:
        case 0x07:
        case 0x0f:
        case 0x13:
        case 0x17:
        case 0x1b:
        case 0x1f:
            return "SLO";
        case 0x23:
        case 0x27:
        case 0x2f:
        case 0x33:
        case 0x37:
        case 0x3b:
        case 0x3f:
            return "RLA";
        case 0x43:
        case 0x47:
        case 0x4f:
        case 0x53:
        case 0x57:
        case 0x5b:
        case 0x5f:
            return "SRE";
        case 0x4b:
            return "ALR";
        case 0x63:
        case 0x67:
        case 0x6f:
        case 0x73:
        case 0x77:
        case 0x7b:
        case 0x7f:
            return "RRA";
        case 0x6b:
            return "ARR";
        case 0x83:
        case 0x87:
        case 0x8f:
        case 0x97:
            return "SAX";
        case 0x8b:
            return "XAA";
        case 0x93:
        case 0x9f:
            return "AHX";
        case 0x9b:
            return "TAS";
        case 0xa3:
        case 0xa7:
        case 0xab:
        case 0xaf:
        case 0xb3:
        case 0xb7:
        case 0xbb:
        case 0xbf:
            return "LAX";
        case 0xc3:
        case 0xc7:
        case 0xcf:
        case 0xd3:
        case 0xd7:
        case 0xdb:
        case 0xdf:
            return "DCP";
        case 0xcb:
            return "AXS";
        case 0xe3:
        case 0xe7:
        case 0xef:
        case 0xf3:
        case 0xf7:
        case 0xfb:
        case 0xff:
            return "ISC";
        case 0xeb:
            return "SBC";

        case 0x06:
        case 0x0a:
        case 0x0e:
        case 0x16:
        case 0x1e:
            return "ASL";
        case 0x26:
        case 0x2a:
        case 0x2e:
        case 0x36:
        case 0x3e:
            return "ROL";
        case 0x46:
        case 0x4a:
        case 0x4e:
        case 0x56:
        case 0x5e:
            return "LSR";
        case 0x66:
        case 0x6a:
        case 0x6e:
        case 0x76:
        case 0x7e:
            return "ROR";
        case 0x86:
        case 0x8e:
        case 0x96:
            return "STX";
        case 0x8a:
            return "TXA";
        case 0x9a:
        case 0xba:
            return "TSX";
        case 0x9e:
            return "SHX";
        case 0xa2:
        case 0xa6:
        case 0xae:
        case 0xb6:
        case 0xbe:
            return "LDX";
        case 0xaa:
            return "TAX";
        case 0xc6:
        case 0xca:
        case 0xce:
        case 0xd6:
        case 0xde:
            return "DEC";
        case 0xe6:
        case 0xee:
        case 0xf6:
        case 0xfe:
            return "INC";

        case 0x02:
        case 0x12:
        case 0x22:
        case 0x32:
        case 0x42:
        case 0x52:
        case 0x62:
        case 0x72:
        case 0x92:
        case 0xb2:
        case 0xd2:
        case 0xf2:
            return "STP";
        case 0x04:
        case 0x0c:
        case 0x14:
        case 0x1c:
        case 0x1a:
        case 0x34:
        case 0x3a:
        case 0x3c:
        case 0x44:
        case 0x54:
        case 0x5a:
        case 0x5c:
        case 0x64:
        case 0x74:
        case 0x7a:
        case 0x7c:
        case 0x80:
        case 0x82:
        case 0x89:
        case 0xc2:
        case 0xd4:
        case 0xda:
        case 0xdc:
        case 0xe2:
        case 0xea:
        case 0xf4:
        case 0xfa:
        case 0xfc:
            return "NOP";

        default:
            assert(false);
    }
}