lzss.cpp

/**************************************************************************************
   INCLUDE
 **************************************************************************************/

#include "mbed.h"
#include "FlashIAPBlockDevice.h"

#include "lzss.h"

#include <stdlib.h>
#include <stdint.h>

/**************************************************************************************
   DEFINE
 **************************************************************************************/

#define EI 11             /* typically 10..13 */
#define EJ  4             /* typically 4..5 */
#define P   1             /* If match length <= P then output one character */
#define N (1 << EI)       /* buffer size */
#define F ((1 << EJ) + 1) /* lookahead buffer size */

#define LZSS_EOF       (-1)

#define FPUTC_BUF_SIZE (256)
#define FGETC_BUF_SIZE (256)

/**************************************************************************************
   GLOBAL VARIABLES
 **************************************************************************************/

extern const char * UPDATE_FILE_NAME_LZSS;

static uint32_t SKETCH_START = 0;
static uint32_t LZSS_FILE_SIZE = 0;
static FILE* update_file = 0;
static FlashIAP* flash;

int bit_buffer = 0, bit_mask = 128;
unsigned char buffer[N * 2];

static char write_buf[FPUTC_BUF_SIZE];
static size_t write_buf_num_bytes = 0;
static size_t bytes_written_fputc = 0;
static size_t bytes_written_flash = 0;
static uint32_t flash_addr = 0;

/**************************************************************************************
   PUBLIC FUNCTIONS
 **************************************************************************************/

void lzss_init(FILE* update_file_ptr, FlashIAP* _flash, uint32_t const sketch_start, uint32_t const lzss_file_size)
{
  SKETCH_START = sketch_start;
  flash_addr = sketch_start + XIP_BASE;
  update_file = update_file_ptr;
  LZSS_FILE_SIZE = lzss_file_size;
  flash = _flash;
}

void lzss_flush()
{
  bytes_written_fputc += write_buf_num_bytes;

  /* Only write to the flash once we've surpassed
   * the SSU in the update binary.
   */
  if (bytes_written_fputc > SKETCH_START)
  {
    flash->program(write_buf, flash_addr, write_buf_num_bytes);
    flash_addr += write_buf_num_bytes;
  }
  
  write_buf_num_bytes = 0;
}

/**************************************************************************************
   PRIVATE FUNCTIONS
 **************************************************************************************/

void lzss_fputc(int const c)
{
  /* Buffer the decompressed data into a buffer so
   * we can perform block writes and don't need to
   * write every byte singly on the flash (which 
   * wouldn't be possible anyway).
   */
  write_buf[write_buf_num_bytes] = static_cast<char>(c);
  write_buf_num_bytes++;

  /* The write buffer is full of decompressed
   * data, write it to the flash now.
   */
  if (write_buf_num_bytes == FPUTC_BUF_SIZE)
    lzss_flush();
}

int lzss_fgetc()
{
  static uint8_t read_buf[FGETC_BUF_SIZE];
  static size_t read_buf_pos = FGETC_BUF_SIZE;
  static size_t bytes_read_fgetc = 0;
  static size_t bytes_read_from_modem = 0;

  /* lzss_file_size is set within SSUBoot:main 
   * and contains the size of the LZSS file. Once
   * all those bytes have been read its time to return
   * LZSS_EOF in order to signal that the end of
   * the file has been reached.
   */
  if (bytes_read_fgetc == LZSS_FILE_SIZE)
    return LZSS_EOF;

  /* If there is no data left to be read from the read buffer
   * than read a new block and store it into the read buffer.
   */
  if (read_buf_pos == FGETC_BUF_SIZE)
  {
    /* Read the next block from the flash memory. */
    bytes_read_from_modem += fread(read_buf, 1, FGETC_BUF_SIZE, update_file);
    /* Reset the read buffer position. */
    read_buf_pos = 0;
  }

  uint8_t const c = read_buf[read_buf_pos];
  read_buf_pos++;
  bytes_read_fgetc++;

  return c;
}

/**************************************************************************************
   LZSS FUNCTIONS
 **************************************************************************************/

void putbit1(void)
{
    bit_buffer |= bit_mask;
    if ((bit_mask >>= 1) == 0) {
        lzss_fputc(bit_buffer);
        bit_buffer = 0;  bit_mask = 128;
    }
}

void putbit0(void)
{
    if ((bit_mask >>= 1) == 0) {
        lzss_fputc(bit_buffer);
        bit_buffer = 0;  bit_mask = 128;
    }
}

void output1(int c)
{
    int mask;
    
    putbit1();
    mask = 256;
    while (mask >>= 1) {
        if (c & mask) putbit1();
        else putbit0();
    }
}

void output2(int x, int y)
{
    int mask;
    
    putbit0();
    mask = N;
    while (mask >>= 1) {
        if (x & mask) putbit1();
        else putbit0();
    }
    mask = (1 << EJ);
    while (mask >>= 1) {
        if (y & mask) putbit1();
        else putbit0();
    }
}

int getbit(int n) /* get n bits */
{
    int i, x;
    static int buf, mask = 0;
    
    x = 0;
    for (i = 0; i < n; i++) {
        if (mask == 0) {
            if ((buf = lzss_fgetc()) == LZSS_EOF) return LZSS_EOF;
            mask = 128;
        }
        x <<= 1;
        if (buf & mask) x++;
        mask >>= 1;
    }
    return x;
}

void lzss_decode(void)
{
    int i, j, k, r, c;
    
    for (i = 0; i < N - F; i++) buffer[i] = ' ';
    r = N - F;
    while ((c = getbit(1)) != LZSS_EOF) {
        if (c) {
            if ((c = getbit(8)) == LZSS_EOF) break;
            lzss_fputc(c);
            buffer[r++] = c;  r &= (N - 1);
        } else {
            if ((i = getbit(EI)) == LZSS_EOF) break;
            if ((j = getbit(EJ)) == LZSS_EOF) break;
            for (k = 0; k <= j + 1; k++) {
                c = buffer[(i + k) & (N - 1)];
                lzss_fputc(c);
                buffer[r++] = c;  r &= (N - 1);
            }
        }
    }
}