windows-nt/Source/XPSP1/NT/enduser/stuff/itss/lzx/encoder/io.c

/*
 * io.c
 */
#include "encoder.h"

/*
 * Similar to the optimisation we have for the decoder.
 *
 * Allow the encoder to "overrun" output buffer by up to X bytes
 * so that we don't have to check for the end of the buffer every
 * single time we call outbits() in encdata.c
 */
#define OUTPUT_EXTRA_BYTES 64


static void encoder_translate_e8(t_encoder_context *context, byte *mem, long bytes);


void output_bits(t_encoder_context *context, int n, ulong x)
{
	context->enc_bitbuf |= (((ulong) x) << (context->enc_bitcount - n));
	context->enc_bitcount -= (signed char) n;     
   
	while (context->enc_bitcount <= 16)                     
	{                                              
		if (context->enc_output_buffer_curpos >= context->enc_output_buffer_end)
        {
            context->enc_output_overflow = true;
            context->enc_output_buffer_curpos = context->enc_output_buffer_start;
        }

        *context->enc_output_buffer_curpos++ = (byte) ((context->enc_bitbuf >> 16) & 255);
        *context->enc_output_buffer_curpos++ = (byte) (context->enc_bitbuf >> 24);

		context->enc_bitbuf <<= 16;
		context->enc_bitcount += 16;                         
	}                                              
}


/*
 * Initialises output buffering
 */
bool init_compressed_output_buffer(t_encoder_context *context)
{
	if (!(context->enc_output_buffer_start = (byte *) context->enc_malloc(OUTPUT_BUFFER_SIZE)))
		return false;

	context->enc_output_buffer_curpos = context->enc_output_buffer_start;

	context->enc_output_buffer_end =
		context->enc_output_buffer_start+(OUTPUT_BUFFER_SIZE-OUTPUT_EXTRA_BYTES);

	return true;
}


void free_compressed_output_buffer(t_encoder_context *context)
{
   if (context->enc_output_buffer_start)
   {
	  context->enc_free(context->enc_output_buffer_start);
	  context->enc_output_buffer_start = NULL;
   }
}


void reset_translation(t_encoder_context *context)
{
	context->enc_instr_pos = 0;
}


static long read_input_data(t_encoder_context *context, byte *mem, long amount)
{

	if (amount <= context->enc_input_left)
	{
		memcpy(mem, context->enc_input_ptr, amount);
		context->enc_input_left -= amount;
		context->enc_input_ptr += amount;

		return amount;
	}
	else
	{
		long bytes_read;

		if (context->enc_input_left <= 0)
			return 0;

		bytes_read = context->enc_input_left;

		memcpy(mem, context->enc_input_ptr, context->enc_input_left);
		context->enc_input_ptr += context->enc_input_left;
		context->enc_input_left = 0;

		return bytes_read;
	}
}


long comp_read_input(t_encoder_context *context, ulong BufPos, long Size)
{
	long    bytes_read;

	if (Size <= 0)
		return 0;

	bytes_read = read_input_data(
		context, 
		&context->enc_RealMemWindow[BufPos], 
		Size
	);

	if (bytes_read < 0)
        return 0;

	/*
	 * If no translation being performed for this file
	 */
    if (context->enc_file_size_for_translation == 0 ||
        context->enc_num_cfdata_frames >= E8_CFDATA_FRAME_THRESHOLD)
    {
        context->enc_num_cfdata_frames++;
		return bytes_read;
    }

	encoder_translate_e8(
		context, 
		&context->enc_RealMemWindow[BufPos], 
		bytes_read
	);

    context->enc_num_cfdata_frames++;

	return bytes_read;
}


static void encoder_translate_e8(t_encoder_context *context, byte *mem, long bytes)
{
	long    offset;
	long    absolute;
	ulong   end_instr_pos;
	byte    temp[6];
	byte    *mem_backup;

	if (bytes <= 6)
	{
		context->enc_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->enc_instr_pos + bytes - 6;

	while (1)
	{
		while (*mem++ != 0xE8)
			context->enc_instr_pos++;

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

#if defined(_X86_) 
	offset = *(long *) mem;
#else
		offset   = (long) (
						((ulong)  mem[0])               | 
						(((ulong) mem[1])<<8)   | 
						(((ulong) mem[2])<<16)  |
						(((ulong) mem[3])<<24)
						);
#endif

		absolute = context->enc_instr_pos + offset;

	if (absolute >= 0)
		{
			if ((ulong) absolute < context->enc_file_size_for_translation+context->enc_instr_pos)
			{
				if ((ulong) absolute >= context->enc_file_size_for_translation)
					absolute = offset - context->enc_file_size_for_translation;

#if defined(_X86_) 
				*(ulong *) mem = (ulong) absolute;
#else
				mem[0] = (byte) ((ulong) absolute & 255);
				mem[1] = (byte) (( ((ulong) absolute) >> 8) & 255);
				mem[2] = (byte) (( ((ulong) absolute) >> 16) & 255);
				mem[3] = (byte) (( ((ulong) absolute) >> 24) & 255);
#endif
			}
		}
  
		mem += 4;
		context->enc_instr_pos += 5;
	}

	/* restore the bytes */
	memcpy(&mem_backup[bytes-6], temp, 6);

	context->enc_instr_pos = end_instr_pos + 6;
}