visualboyadvance-m/fex/7z_C/Bra86.c

/* Bra86.c -- Converter for x86 code (BCJ)
2008-10-04 : Igor Pavlov : Public domain */

#include "Bra.h"

#define Test86MSByte(b) ((b) == 0 || (b) == 0xFF)

const Byte kMaskToAllowedStatus[8] = { 1, 1, 1, 0, 1, 0, 0, 0 };
const Byte kMaskToBitNumber[8] = { 0, 1, 2, 2, 3, 3, 3, 3 };

SizeT x86_Convert(Byte* data, SizeT size, UInt32 ip, UInt32* state, int encoding)
{
    SizeT bufferPos = 0, prevPosT;
    UInt32 prevMask = *state & 0x7;
    if (size < 5)
        return 0;
    ip += 5;
    prevPosT = (SizeT)0 - 1;

    for (;;) {
        Byte* p = data + bufferPos;
        Byte* limit = data + size - 4;
        for (; p < limit; p++)
            if ((*p & 0xFE) == 0xE8)
                break;
        bufferPos = (SizeT)(p - data);
        if (p >= limit)
            break;
        prevPosT = bufferPos - prevPosT;
        if (prevPosT > 3)
            prevMask = 0;
        else {
            prevMask = (prevMask << ((int)prevPosT - 1)) & 0x7;
            if (prevMask != 0) {
                Byte b = p[4 - kMaskToBitNumber[prevMask]];
                if (!kMaskToAllowedStatus[prevMask] || Test86MSByte(b)) {
                    prevPosT = bufferPos;
                    prevMask = ((prevMask << 1) & 0x7) | 1;
                    bufferPos++;
                    continue;
                }
            }
        }
        prevPosT = bufferPos;

        if (Test86MSByte(p[4])) {
            UInt32 src = ((UInt32)p[4] << 24) | ((UInt32)p[3] << 16) | ((UInt32)p[2] << 8) | ((UInt32)p[1]);
            UInt32 dest;
            for (;;) {
                Byte b;
                int index;
                if (encoding)
                    dest = (ip + (UInt32)bufferPos) + src;
                else
                    dest = src - (ip + (UInt32)bufferPos);
                if (prevMask == 0)
                    break;
                index = kMaskToBitNumber[prevMask] * 8;
                b = (Byte)(dest >> (24 - index));
                if (!Test86MSByte(b))
                    break;
                src = dest ^ ((1 << (32 - index)) - 1);
            }
            p[4] = (Byte)(~(((dest >> 24) & 1) - 1));
            p[3] = (Byte)(dest >> 16);
            p[2] = (Byte)(dest >> 8);
            p[1] = (Byte)dest;
            bufferPos += 5;
        } else {
            prevMask = ((prevMask << 1) & 0x7) | 1;
            bufferPos++;
        }
    }
    prevPosT = bufferPos - prevPosT;
    *state = ((prevPosT > 3) ? 0 : ((prevMask << ((int)prevPosT - 1)) & 0x7));
    return bufferPos;
}