melonDS/src/AREngine.cpp

/*
    Copyright 2016-2020 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;


void ParseTextCode(char* text, u32* code, int len) // or whatever this should be named?
{
    // TODO: they should atleast ensure they parsed all the crap before the actual code. we ain't taking care of that.
    // this is melonDS not kindergarten. seriously.

    u32 cur_word = 0;
    u32 ndigits = 0;
    u32 nout = 0;

    char c;
    while ((c = *text++) != '\0')
    {
        // hope they didn't forget the terminator, either
        // otherwise
        // they will be the ones getting terminated
        // blarg.

        // so, what do we do here.
        u32 val;
        if (c >= '0' && c <= '9')
            val = c - '0';
        else if (c >= 'a' && c <= 'f')
            val = c - 'a' + 0xA;
        else if (c >= 'A' && c <= 'F')
            val = c - 'A' + 0xA;
        else
            continue;

        // okay, there's atleast that.

        cur_word <<= 4;
        cur_word |= val;

        // now I figure we can't keep doing that forever? can we?
        // maybe we can, after all
        // but it's not a good idea.

        ndigits++;
        if (ndigits >= 8)
        {
            if (nout >= len)
            {
                // OH SHIT SHIT SHIT SHIT
                printf("AR: code too long!\n");
                return;
            }

            *code++ = cur_word;
            nout++;

            ndigits = 0;
            cur_word = 0;
        }
    }

    if (nout & 1)
    {
        printf("AR: code was missing one word??\n");
        *code++ = 0;
    }
}


bool Init()
{
    return true;
}

void DeInit()
{
    //
}

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

    // TODO: acquire codes from a sensible source!
#define TEMP_PUTCODE(a, b) *ptr++ = a; *ptr++ = b;
    CheatEntry* entry = &CheatCodes[0];
    u32* ptr = &entry->Code[0];
    // what do we put in here?
    // heh. noone knows. the world is full of mysteries
    // like
    // WHAT IS MY FUCKING GENDER
    // probably I am nonbinary, like Mario
    // oh
    // noone told you?
    // well...
    // also why won't my video save. maybe there is too much crap in this computer.
    // shrug.
    // or why is this text warping weirdly. I should check the video driver.
    // or the video card.
    // well.
    //


    char* test = R"(9209D09A 00000000
6209B468 00000000
B209B468 00000000
10000672 000003FF
D2000000 00000000
9209D09A 00000000
94000130 FCBF0000
6209B468 00000000
B209B468 00000000
200006B3 00000001
200006B4 00000001
D2000000 00000000
9209D09A 00000000
94000130 FC7F0000
6209B468 00000000
B209B468 00000000
10000672 00000000
D2000000 00000000)";
    ParseTextCode(test, entry->Code, 2*64);
    printf("PARSED CODE:\n");
    for (int i = 0; i < 2*64; i+=2)
    {
        printf("%08X %08X\n", entry->Code[i], entry->Code[i+1]);
    }
    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 offset = 0;
    u32 datareg = 0;
    u32 cond = 1;
    u32 condstack = 0;

    u32* loopstart = code;
    u32 loopcount = 0;
    u32 loopcond = 1;
    u32 loopcondstack = 0;

    // TODO: does anything reset this??
    u32 c5count = 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)
            {
                if ((op & 0xF0) == 0xE0)
                {
                    for (u32 i = 0; i < b; i += 8)
                        *code += 2;
                }

                continue;
            }
        }

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

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

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

        case16(0x30): // IF b > u32[a]
            {
                condstack <<= 1;
                condstack |= cond;

                u32 chk = NDS::ARM7Read32(a & 0x0FFFFFFF);

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

        case16(0x40): // IF b < u32[a]
            {
                condstack <<= 1;
                condstack |= cond;

                u32 chk = NDS::ARM7Read32(a & 0x0FFFFFFF);

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

        case16(0x50): // IF b == u32[a]
            {
                condstack <<= 1;
                condstack |= cond;

                u32 chk = NDS::ARM7Read32(a & 0x0FFFFFFF);

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

        case16(0x60): // IF b != u32[a]
            {
                condstack <<= 1;
                condstack |= cond;

                u32 chk = NDS::ARM7Read32(a & 0x0FFFFFFF);

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

        case16(0x70): // 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;

        case16(0x80): // 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;

        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;

        case16(0xA0): // 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;

        case16(0xB0): // offset = u32[a + offset]
            offset = NDS::ARM7Read32((a & 0x0FFFFFFF) + offset);
            break;

        case 0xC0: // FOR 0..b
            loopstart = code; // points to the first opcode after the FOR
            loopcount = b;
            loopcond = cond;           // checkme
            loopcondstack = condstack; // (GBAtek is not very clear there)
            break;

        case 0xC4: // offset = pointer to C4000000 opcode
            // theoretically used for safe storage, by accessing [offset+4]
            // in practice could be used for a self-modifying AR code
            // could be implemented with some hackery, but, does anything even
            // use it??
            printf("AR: !! THE FUCKING C4000000 OPCODE. TELL ARISOTURA.\n");
            return;

        case 0xC5: // count++ / IF (count & b.l) == b.h
            {
                // with weird condition checking, apparently
                // oh well

                c5count++;
                if (!cond) break;

                condstack <<= 1;
                condstack |= cond;

                u16 mask = b & 0xFFFF;
                u16 chk = b >> 16;

                cond = ((c5count & mask) == chk) ? 1:0;
            }
            break;

        case 0xC6: // u32[b] = offset
            NDS::ARM7Write32(b, offset);
            break;

        case 0xD0: // ENDIF
            cond = condstack & 0x1;
            condstack >>= 1;
            break;

        case 0xD1: // NEXT
            if (loopcount > 0)
            {
                loopcount--;
                code = loopstart;
            }
            else
            {
                cond = loopcond;
                condstack = loopcondstack;
            }
            break;

        case 0xD2: // NEXT+FLUSH
            if (loopcount > 0)
            {
                loopcount--;
                code = loopstart;
            }
            else
            {
                offset = 0;
                datareg = 0;
                condstack = 0;
                cond = 1;
            }
            break;

        case 0xD3: // offset = b
            offset = b;
            break;

        case 0xD4: // datareg += b
            datareg += b;
            break;

        case 0xD5: // datareg = b
            datareg = b;
            break;

        case 0xD6: // u32[b+offset] = datareg / offset += 4
            NDS::ARM7Write32(b + offset, datareg);
            offset += 4;
            break;

        case 0xD7: // u16[b+offset] = datareg / offset += 2
            NDS::ARM7Write16(b + offset, datareg & 0xFFFF);
            offset += 2;
            break;

        case 0xD8: // u8[b+offset] = datareg / offset += 1
            NDS::ARM7Write8(b + offset, datareg & 0xFF);
            offset += 1;
            break;

        case 0xD9: // datareg = u32[b+offset]
            datareg = NDS::ARM7Read32(b + offset);
            break;

        case 0xDA: // datareg = u16[b+offset]
            datareg = NDS::ARM7Read16(b + offset);
            break;

        case 0xDB: // datareg = u8[b+offset]
            datareg = NDS::ARM7Read8(b + offset);
            break;

        case 0xDC: // offset += b
            offset += b;
            break;

        case16(0xE0): // copy b param bytes to address a+offset
            {
                // TODO: check for bad alignment of dstaddr

                u32 dstaddr = (a & 0x0FFFFFFF) + offset;
                u32 bytesleft = b;
                while (bytesleft >= 8)
                {
                    NDS::ARM7Write32(dstaddr, *code++); dstaddr += 4;
                    NDS::ARM7Write32(dstaddr, *code++); dstaddr += 4;
                    bytesleft -= 8;
                }
                if (bytesleft > 0)
                {
                    u8* leftover = (u8*)code;
                    *code += 2;
                    if (bytesleft >= 4)
                    {
                        NDS::ARM7Write32(dstaddr, *(u32*)leftover); dstaddr += 4;
                        leftover += 4;
                        bytesleft -= 4;
                    }
                    while (bytesleft > 0)
                    {
                        NDS::ARM7Write8(dstaddr, *leftover++); dstaddr++;
                        bytesleft--;
                    }
                }
            }
            break;

        case16(0xF0): // copy b bytes from address offset to address a
            {
                // TODO: check for bad alignment of srcaddr/dstaddr

                u32 srcaddr = offset;
                u32 dstaddr = (a & 0x0FFFFFFF);
                u32 bytesleft = b;
                while (bytesleft >= 4)
                {
                    NDS::ARM7Write32(dstaddr, NDS::ARM7Read32(srcaddr));
                    srcaddr += 4;
                    dstaddr += 4;
                    bytesleft -= 4;
                }
                while (bytesleft > 0)
                {
                    NDS::ARM7Write8(dstaddr, NDS::ARM7Read8(srcaddr));
                    srcaddr++;
                    dstaddr++;
                    bytesleft--;
                }
            }
            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);
    }
}

}