melonDS/src/AREngine.cpp

/*
    Copyright 2016-2019 Arisotura

    This file is part of melonDS.

    melonDS is free software: you can redistribute it and/or modify it under
    the terms of the GNU General Public License as published by the Free
    Software Foundation, either version 3 of the License, or (at your option)
    any later version.

    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with melonDS. If not, see http://www.gnu.org/licenses/.
*/

#include <stdio.h>
#include <string.h>
#include "NDS.h"
#include "AREngine.h"


namespace AREngine
{

typedef struct
{
    u32 Code[2 * 64]; // TODO: more sensible size for this? allocate on demand?
    bool Enabled;

} CheatEntry;

// TODO: more sensible size for this? allocate on demand?
CheatEntry CheatCodes[64];
u32 NumCheatCodes;


bool Init()
{
    return true;
}

void DeInit()
{
    //
}

void Reset()
{
    memset(CheatCodes, 0, sizeof(CheatCodes));
    NumCheatCodes = 0;

    // TODO: acquire codes from a sensible source!
    CheatEntry* entry = &CheatCodes[0];
    u32* ptr = &entry->Code[0];
#define TEMP_PUTCODE(a, b) *ptr++ = a; *ptr++ = b;
    // NSMBDS EUR - giant fucking Mario
    TEMP_PUTCODE(0x1209DBD0, 0x0000027C);
    TEMP_PUTCODE(0x2209DBC0, 0x00000003);
    TEMP_PUTCODE(0x94000130, 0xFFFD0000);
    TEMP_PUTCODE(0x1209DBD0, 0x00000000);
    TEMP_PUTCODE(0x2209DBC0, 0x00000003);
    entry->Enabled = true;
    NumCheatCodes++;
}


#define case16(x) \
    case ((x)+0x00): case ((x)+0x01): case ((x)+0x02): case ((x)+0x03): \
    case ((x)+0x04): case ((x)+0x05): case ((x)+0x06): case ((x)+0x07): \
    case ((x)+0x08): case ((x)+0x09): case ((x)+0x0A): case ((x)+0x0B): \
    case ((x)+0x0C): case ((x)+0x0D): case ((x)+0x0E): case ((x)+0x0F)

void RunCheat(CheatEntry* entry)
{
    u32* code = &entry->Code[0];

    u32 cond = 1;
    u32 condstack = 0;

    for (;;)
    {
        u32 a = *code++;
        u32 b = *code++;
        if ((a|b) == 0) break;

        u8 op = a >> 24;

        if ((op < 0xD0 && op != 0xC5) || op > 0xD2)
        {
            if (!cond)
            {
                // TODO: skip parameters for opcode Ex
                continue;
            }
        }

        switch (op)
        {
        case16(0x00): // 32-bit write
            NDS::ARM7Write32(a & 0x0FFFFFFF, b);
            break;

        case16(0x10): // 16-bit write
            NDS::ARM7Write16(a & 0x0FFFFFFF, b & 0xFFFF);
            break;

        case16(0x20): // 8-bit write
            NDS::ARM7Write8(a & 0x0FFFFFFF, b & 0xFF);
            break;

        case16(0x90): // IF b.l = ((~b.h) & u16[a])
            {
                condstack <<= 1;
                condstack |= cond;

                u16 val = NDS::ARM7Read16(a & 0x0FFFFFFF);
                u16 chk = ~(b >> 16);
                chk &= val;

                cond = ((b & 0xFFFF) == chk) ? 1:0;
            }
            break;

        default:
            printf("!! bad AR opcode %08X %08X\n", a, b);
            return;
        }
    }
}

void RunCheats()
{
    // TODO: make it disableable in general

    for (u32 i = 0; i < NumCheatCodes; i++)
    {
        CheatEntry* entry = &CheatCodes[i];
        if (entry->Enabled)
            RunCheat(entry);
    }
}

}