User:Simpsons contributor/Compressor

package FractalProcessor;

// ==============================================================================

import java.io.IOException;

// Adapted from Jef Poskanzer's Java port by way of J. M. G. Elliott. import java.io.OutputStream; // K Weiner 12/00

class LZWEncoder {

private static final int EOF = -1;

private int imgW, imgH;

private byte[] pixAry;

private int initCodeSize;

private int remaining;

private int curPixel;

// GIFCOMPR.C - GIF Image compression routines // // Lempel-Ziv compression based on 'compress'. GIF modifications by // David Rowley (mgardi@watdcsu.waterloo.edu)

// General DEFINEs

static final int BITS = 12;

static final int HSIZE = 5003; // 80% occupancy

// GIF Image compression - modified 'compress' // // Based on: compress.c - File compression ala IEEE Computer, June 1984. // // By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas) // Jim McKie (decvax!mcvax!jim) // Steve Davies (decvax!vax135!petsd!peora!srd) // Ken Turkowski (decvax!decwrl!turtlevax!ken) // James A. Woods (decvax!ihnp4!ames!jaw) // Joe Orost (decvax!vax135!petsd!joe)

int n_bits; // number of bits/code

int maxbits = BITS; // user settable max # bits/code

int maxcode; // maximum code, given n_bits

int maxmaxcode = 1 << BITS; // should NEVER generate this code

int[] htab = new int[HSIZE];

int[] codetab = new int[HSIZE];

int hsize = HSIZE; // for dynamic table sizing

int free_ent = 0; // first unused entry

// block compression parameters -- after all codes are used up, // and compression rate changes, start over. boolean clear_flg = false;

// Algorithm: use open addressing double hashing (no chaining) on the // prefix code / next character combination. We do a variant of Knuth's // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime // secondary probe. Here, the modular division first probe is gives way // to a faster exclusive-or manipulation. Also do block compression with // an adaptive reset, whereby the code table is cleared when the compression // ratio decreases, but after the table fills. The variable-length output // codes are re-sized at this point, and a special CLEAR code is generated // for the decompressor. Late addition: construct the table according to // file size for noticeable speed improvement on small files. Please direct // questions about this implementation to ames!jaw.

int g_init_bits;

int ClearCode;

int EOFCode;

// output // // Output the given code. // Inputs: // code: A n_bits-bit integer. If == -1, then EOF. This assumes // that n_bits =< wordsize - 1. // Outputs: // Outputs code to the file. // Assumptions: // Chars are 8 bits long. // Algorithm: // Maintain a BITS character long buffer (so that 8 codes will // fit in it exactly). Use the VAX insv instruction to insert each // code in turn. When the buffer fills up empty it and start over.

int cur_accum = 0;

int cur_bits = 0;

int masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };

// Number of characters so far in this 'packet' int a_count;

// Define the storage for the packet accumulator byte[] accum = new byte[256];

//  LZWEncoder(int width, int height, byte[] pixels, int color_depth) { imgW = width; imgH = height; pixAry = pixels; initCodeSize = Math.max(2, color_depth); }

// Add a character to the end of the current packet, and if it is 254 // characters, flush the packet to disk. void char_out(byte c, OutputStream outs) throws IOException { accum[a_count++] = c;   if (a_count >= 254) flush_char(outs); }

// Clear out the hash table

// table clear for block compress void cl_block(OutputStream outs) throws IOException { cl_hash(hsize); free_ent = ClearCode + 2; clear_flg = true;

output(ClearCode, outs); }

// reset code table void cl_hash(int hsize) { for (int i = 0; i < hsize; ++i) htab[i] = -1; }

void compress(int init_bits, OutputStream outs) throws IOException { int fcode; int i /* = 0 */; int c;   int ent; int disp; int hsize_reg; int hshift;

// Set up the globals: g_init_bits - initial number of bits g_init_bits = init_bits;

// Set up the necessary values clear_flg = false; n_bits = g_init_bits; maxcode = MAXCODE(n_bits);

ClearCode = 1 << (init_bits - 1); EOFCode = ClearCode + 1; free_ent = ClearCode + 2;

a_count = 0; // clear packet

ent = nextPixel;

hshift = 0; for (fcode = hsize; fcode < 65536; fcode *= 2) ++hshift; hshift = 8 - hshift; // set hash code range bound

hsize_reg = hsize; cl_hash(hsize_reg); // clear hash table

output(ClearCode, outs);

outer_loop: while ((c = nextPixel) != EOF) { fcode = (c << maxbits) + ent; i = (c << hshift) ^ ent; // xor hashing

if (htab[i] == fcode) { ent = codetab[i]; continue; } else if (htab[i] >= 0) // non-empty slot {       disp = hsize_reg - i; // secondary hash (after G. Knott) if (i == 0) disp = 1; do { if ((i -= disp) < 0) i += hsize_reg;

if (htab[i] == fcode) { ent = codetab[i]; continue outer_loop; }       } while (htab[i] >= 0); }     output(ent, outs); ent = c;     if (free_ent < maxmaxcode) { codetab[i] = free_ent++; // code -> hashtable htab[i] = fcode; } else cl_block(outs); }   // Put out the final code. output(ent, outs); output(EOFCode, outs); }

//  void encode(OutputStream os) throws IOException { os.write(initCodeSize); // write "initial code size" byte

remaining = imgW * imgH; // reset navigation variables curPixel = 0;

compress(initCodeSize + 1, os); // compress and write the pixel data

os.write(0); // write block terminator }

// Flush the packet to disk, and reset the accumulator void flush_char(OutputStream outs) throws IOException { if (a_count > 0) { outs.write(a_count); outs.write(accum, 0, a_count); a_count = 0; } }

final int MAXCODE(int n_bits) { return (1 << n_bits) - 1; }

//  // Return the next pixel from the image //  private int nextPixel { if (remaining == 0) return EOF;

--remaining;

byte pix = pixAry[curPixel++];

return pix & 0xff; }

void output(int code, OutputStream outs) throws IOException { cur_accum &= masks[cur_bits];

if (cur_bits > 0) cur_accum |= (code << cur_bits); else cur_accum = code;

cur_bits += n_bits;

while (cur_bits >= 8) { char_out((byte) (cur_accum & 0xff), outs); cur_accum >>= 8; cur_bits -= 8; }

// If the next entry is going to be too big for the code size, // then increase it, if possible. if (free_ent > maxcode || clear_flg) { if (clear_flg) { maxcode = MAXCODE(n_bits = g_init_bits); clear_flg = false; } else { ++n_bits; if (n_bits == maxbits) maxcode = maxmaxcode; else maxcode = MAXCODE(n_bits); }   }

if (code == EOFCode) { // At EOF, write the rest of the buffer. while (cur_bits > 0) { char_out((byte) (cur_accum & 0xff), outs); cur_accum >>= 8; cur_bits -= 8; }

flush_char(outs); } } }