windows-xp/Source/XPSP1/NT/base/mspatch/lzx/decoder/decxlat.c

/*
 * xlat.c
 *
 * Translate
 */
#include "decoder.h"

#include <memory.h>
#pragma intrinsic(memcpy,memset)

void NEAR init_decoder_translation(t_decoder_context *context)
{
    context->dec_instr_pos = 0;
}


#ifdef ASM_TRANSLATE_E8
ulong __cdecl asm_decoder_translate_e8(ulong instr_pos, ulong file_size, byte *mem, long bytes);

void NEAR decoder_translate_e8(t_decoder_context *context, byte *mem, long bytes)
{
    /*
     * We don't want the ASM code to have to worry about where in the
     * context structure a particular element is
     */
    context->dec_instr_pos = asm_decoder_translate_e8(
                                                     context->dec_instr_pos,
                                                     context->dec_current_file_size,
                                                     mem,
                                                     bytes
                                                     );
}

#else /* !ASM_TRANSLATE_E8 */

void NEAR decoder_translate_e8(t_decoder_context *context, byte *mem, long bytes)
{
    ulong   end_instr_pos;
    byte    temp[6];
    byte    *mem_backup;

    if (bytes <= 6)
        {
        context->dec_instr_pos += bytes;
        return;
        }

    mem_backup = mem;

    /* backup these bytes */
    memcpy(temp, &mem[bytes-6], 6);

    /* overwrite them with 0xE8 */
    memset(&mem[bytes-6], 0xE8, 6);

    end_instr_pos = context->dec_instr_pos + bytes - 6;

    while (1)
        {
        unsigned long   absolute;

        /*
         * We are guaranteed to hit one of the 6 0xE8's we stuck at the
         * end of the buffer, even if we ran into some corrupted data
         * that resulted in our jumping over 5 bytes due to a translation
         */
        while (*mem++ != 0xE8)
            context->dec_instr_pos++;

        if (context->dec_instr_pos >= end_instr_pos)
            break;

        /*
         * There are 5 or more bytes in the buffer
         * (i.e. E8 xx xx xx xx)
         *
         * We have a complete offset available to (potentially) translate
         */

        absolute = *(UNALIGNED ulong *) mem;

        if (absolute < context->dec_current_file_size)
            {
            /* absolute >= 0 && absolute < dec_current_file_size */

            *(UNALIGNED ulong *) mem = absolute - context->dec_instr_pos;
            }
        else if ((ulong) (-(long) absolute) <= context->dec_instr_pos)
            {
            /* absolute >= -instr_pos && absolute < 0 */

            *(UNALIGNED ulong *) mem = absolute + context->dec_current_file_size;
            }

        mem += 4;
        context->dec_instr_pos += 5;
        }

    context->dec_instr_pos = end_instr_pos + 6;

    /* restore these bytes */
    memcpy(&mem_backup[bytes-6], temp, 6);
}
#endif