335 lines
9.1 KiB
Java
335 lines
9.1 KiB
Java
package com.wf.captcha;
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import java.io.IOException;
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import java.io.OutputStream;
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/**
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*
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*/
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public class Encoder {
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private static final int EOF = -1;
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// 图片的宽高
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private int imgW, imgH;
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private byte[] pixAry;
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private int initCodeSize; // 验证码位数
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private int remaining; // 剩余数量
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private int curPixel; // 像素
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static final int BITS = 12;
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static final int HSIZE = 5003; // 80% 占用率
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int n_bits; // number of bits/code
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int maxbits = BITS; // user settable max # bits/code
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int maxcode; // maximum code, given n_bits
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int maxmaxcode = 1 << BITS; // should NEVER generate this code
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int[] htab = new int[HSIZE];
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int[] codetab = new int[HSIZE];
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int hsize = HSIZE; // for dynamic table sizing
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int free_ent = 0; // first unused entry
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// block compression parameters -- after all codes are used up,
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// and compression rate changes, start over.
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boolean clear_flg = false;
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// Algorithm: use open addressing double hashing (no chaining) on the
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// prefix code / next character combination. We do a variant of Knuth's
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// algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
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// secondary probe. Here, the modular division first probe is gives way
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// to a faster exclusive-or manipulation. Also do block compression with
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// an adaptive reset, whereby the code table is cleared when the compression
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// ratio decreases, but after the table fills. The variable-length output
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// codes are re-sized at this point, and a special CLEAR code is generated
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// for the decompressor. Late addition: construct the table according to
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// file size for noticeable speed improvement on small files. Please direct
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// questions about this implementation to ames!jaw.
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int g_init_bits;
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int ClearCode;
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int EOFCode;
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// output
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//
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// Output the given code.
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// Inputs:
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// code: A n_bits-bit integer. If == -1, then EOF. This assumes
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// that n_bits =< wordsize - 1.
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// Outputs:
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// Outputs code to the file.
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// Assumptions:
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// Chars are 8 bits long.
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// Algorithm:
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// Maintain a BITS character long buffer (so that 8 codes will
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// fit in it exactly). Use the VAX insv instruction to insert each
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// code in turn. When the buffer fills up empty it and start over.
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int cur_accum = 0;
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int cur_bits = 0;
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int masks[] =
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{
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0x0000,
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0x0001,
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0x0003,
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0x0007,
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0x000F,
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0x001F,
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0x003F,
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0x007F,
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0x00FF,
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0x01FF,
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0x03FF,
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0x07FF,
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0x0FFF,
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0x1FFF,
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0x3FFF,
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0x7FFF,
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0xFFFF};
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// Number of characters so far in this 'packet'
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int a_count;
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// Define the storage for the packet accumulator
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byte[] accum = new byte[256];
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//----------------------------------------------------------------------------
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/**
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* @param width 宽度
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* @param height 高度
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* @param pixels 像素
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* @param color_depth 颜色
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*/
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Encoder(int width, int height, byte[] pixels, int color_depth) {
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imgW = width;
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imgH = height;
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pixAry = pixels;
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initCodeSize = Math.max(2, color_depth);
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}
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// Add a character to the end of the current packet, and if it is 254
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// characters, flush the packet to disk.
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/**
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* @param c 字节
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* @param outs 输出流
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* @throws IOException IO异常
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*/
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void char_out(byte c, OutputStream outs) throws IOException {
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accum[a_count++] = c;
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if (a_count >= 254)
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flush_char(outs);
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}
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// Clear out the hash table
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// table clear for block compress
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/**
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* @param outs 输出流
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* @throws IOException IO异常
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*/
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void cl_block(OutputStream outs) throws IOException {
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cl_hash(hsize);
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free_ent = ClearCode + 2;
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clear_flg = true;
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output(ClearCode, outs);
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}
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// reset code table
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/**
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* @param hsize int
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*/
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void cl_hash(int hsize) {
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for (int i = 0; i < hsize; ++i)
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htab[i] = -1;
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}
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/**
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* @param init_bits int
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* @param outs 输出流
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* @throws IOException IO异常
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*/
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void compress(int init_bits, OutputStream outs) throws IOException {
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int fcode;
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int i /* = 0 */;
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int c;
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int ent;
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int disp;
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int hsize_reg;
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int hshift;
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// Set up the globals: g_init_bits - initial number of bits
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g_init_bits = init_bits;
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// Set up the necessary values
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clear_flg = false;
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n_bits = g_init_bits;
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maxcode = MAXCODE(n_bits);
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ClearCode = 1 << (init_bits - 1);
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EOFCode = ClearCode + 1;
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free_ent = ClearCode + 2;
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a_count = 0; // clear packet
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ent = nextPixel();
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hshift = 0;
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for (fcode = hsize; fcode < 65536; fcode *= 2)
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++hshift;
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hshift = 8 - hshift; // set hash code range bound
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hsize_reg = hsize;
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cl_hash(hsize_reg); // clear hash table
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output(ClearCode, outs);
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outer_loop:
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while ((c = nextPixel()) != EOF) {
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fcode = (c << maxbits) + ent;
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i = (c << hshift) ^ ent; // xor hashing
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if (htab[i] == fcode) {
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ent = codetab[i];
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continue;
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} else if (htab[i] >= 0) // non-empty slot
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{
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disp = hsize_reg - i; // secondary hash (after G. Knott)
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if (i == 0)
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disp = 1;
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do {
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if ((i -= disp) < 0)
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i += hsize_reg;
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if (htab[i] == fcode) {
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ent = codetab[i];
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continue outer_loop;
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}
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} while (htab[i] >= 0);
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}
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output(ent, outs);
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ent = c;
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if (free_ent < maxmaxcode) {
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codetab[i] = free_ent++; // code -> hashtable
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htab[i] = fcode;
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} else
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cl_block(outs);
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}
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// Put out the final code.
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output(ent, outs);
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output(EOFCode, outs);
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}
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//----------------------------------------------------------------------------
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/**
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* @param os 输出流
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* @throws IOException IO异常
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*/
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void encode(OutputStream os) throws IOException {
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os.write(initCodeSize); // write "initial code size" byte
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remaining = imgW * imgH; // reset navigation variables
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curPixel = 0;
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compress(initCodeSize + 1, os); // compress and write the pixel data
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os.write(0); // write block terminator
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}
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// Flush the packet to disk, and reset the accumulator
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/**
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* @param outs 输出流
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* @throws IOException IO异常
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*/
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void flush_char(OutputStream outs) throws IOException {
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if (a_count > 0) {
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outs.write(a_count);
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outs.write(accum, 0, a_count);
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a_count = 0;
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}
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}
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/**
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* @param n_bits int
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* @return int
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*/
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final int MAXCODE(int n_bits) {
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return (1 << n_bits) - 1;
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}
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//----------------------------------------------------------------------------
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// Return the next pixel from the image
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//----------------------------------------------------------------------------
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/**
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* @return int
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*/
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private int nextPixel() {
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if (remaining == 0)
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return EOF;
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--remaining;
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byte pix = pixAry[curPixel++];
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return pix & 0xff;
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}
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/**
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* @param code int
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* @param outs 输出流
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* @throws IOException IO异常
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*/
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void output(int code, OutputStream outs) throws IOException {
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cur_accum &= masks[cur_bits];
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if (cur_bits > 0)
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cur_accum |= (code << cur_bits);
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else
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cur_accum = code;
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cur_bits += n_bits;
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while (cur_bits >= 8) {
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char_out((byte) (cur_accum & 0xff), outs);
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cur_accum >>= 8;
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cur_bits -= 8;
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}
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// If the next entry is going to be too big for the code size,
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// then increase it, if possible.
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if (free_ent > maxcode || clear_flg) {
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if (clear_flg) {
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maxcode = MAXCODE(n_bits = g_init_bits);
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clear_flg = false;
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} else {
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++n_bits;
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if (n_bits == maxbits)
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maxcode = maxmaxcode;
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else
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maxcode = MAXCODE(n_bits);
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}
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}
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if (code == EOFCode) {
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// At EOF, write the rest of the buffer.
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while (cur_bits > 0) {
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char_out((byte) (cur_accum & 0xff), outs);
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cur_accum >>= 8;
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cur_bits -= 8;
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}
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flush_char(outs);
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}
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}
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}
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