LZ77 压缩算法 js实现

lz77 压缩算法 JS实现, 参考了网上的一个例子, 重写过的, 压缩效果一般

 

 

function lz77_c(str){// 将字符串转换为 UTF-8 字节数组 function str_to_utf8(str) {var r = [];for(var i=0;i<str.length;i++) {var ch = str.charCodeAt(i);if(ch <= 0x7f)r[r.length] = ch;else if(ch<= 0x7ff) {r[r.length] = 0xC0 | (ch>>6);r[r.length] = 0x80 | (ch & 0x3F);} else if(ch<= 0xFFFF) {r[r.length] = 0xE0 | (ch>>12);r[r.length] = 0x80 | ((ch>>6) & 0x3F);r[r.length] = 0x80 | (ch & 0x3F);}}return r;}str = str_to_utf8(str);var X = 1<<15 /* 距离用15位二进制表示*/, L = 32 /* 匹配长度用5位二进制*/;// 在字符串 str 中 比较a,b位置处的最长匹配function strcmp(str, a, b) {var i = 0, sl = str.length;for(;i< L && a+i<sl && b+i<sl;i++)if(str[a+i] != str[b+i])return i;return i<L?i:L;}// 三字节字符串位置索引 {"abc":[3,7,19],"def":[2,23]}var dic = {};// 存放结果的数组 每单元存放 24个二进制位 (3个字节)// 第一单元用于表示最后一个单元剩余未用的二进制位数量var r = [0];// 向数组r中写入值为v的n位二进制数function write_bits(r, v, n) {if(n<=0)return;if(r[0] == 0) {r[r.length] = 0;r[0] = 24;}if(n < r[0]) {r[0] -= nr[r.length-1] |= v<<r[0];}else{var n1 = n - r[0];r[r.length-1] |= v>>n1;r[0] = 0;write_bits(r, v & (0xffffff >> (24-n1)), n1);}}// 扫描字符串开始编码for(var i=0;i<str.length;i++){var max_len=0, max_off=0;// 最长匹配和位置if( i< str.length-3) {var d1 = String.fromCharCode(str[i],str[i+1],str[i+2]); //三字节字符串加入索引if(dic[d1]) {dic[d1].push(i);}else{dic[d1] = [i];}for(var k=dic[d1].length-2; k>=0; k--) {var j = dic[d1][k];if(j <= i - X) {break;}var len = strcmp(str, i, j); //在索引位置处查找最长匹配if(len > max_len) {max_len = len;max_off = i - j;}}}if(max_off < X && max_len > 3) { // 找到最长匹配write_bits(r, 1,1); // 写入标识write_bits(r, max_off, 15); // 写入位置write_bits(r, max_len-3, 5); // 写入长度i+= max_len-1;}else{write_bits(r, 0,1); // 没找到 写入标识和原字符write_bits(r, str[i], 8);}}// BASE64 编码var z = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=".split("");var rs = [];for(var i=0;i<r.length;i++) {rs[rs.length] = z[(r[i]>>18) & 0x3f];rs[rs.length] = z[(r[i]>>12) & 0x3f];rs[rs.length] = z[(r[i]>> 6) & 0x3f];rs[rs.length] = z[(r[i] ) & 0x3f];}return rs.join("");}function lz77_d(s){var i,j, ch, z ={}, w = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='.split('');for(i=0;i<64;i++) // base64解码z[w[i]] = i;var r = [], x=1, y=0; // 将BASE64转为整型数组for(i=0,j=0;i<s.length;i+=4,j++)r[j] = (z[s.charAt(i)]<<18) | (z[s.charAt(i+1)]<<12) | (z[s.charAt(i+2)]<<6) | (z[s.charAt(i+3)]);// 读取二进制位 r 数组 n 读取位数 从 x 单元的第 y 位开始读function read_bits(r, n){var v, ny;if(r.length*24 - r[0] - (x*24+y) < n)return -1;ny = 24-y;if(n <= ny) {v = (r[x]>>(ny-n)) & (0xffffff >> (24-n));y += n;if(y==24) {x++;y=0;}return v;}else{v = (r[x] & (0xffffff >> y)) << (n-ny);x++;y=0;v |= read_bits(r, n-ny);return v;}}s = []; //开始解码 结果放到 s 里j=0;for(;;) {var c = read_bits(r, 1); // 读取一位标志位if(c<0)break;if(c==0){s[s.length] = read_bits(r, 8);//读取一个字节j++;}else{var off = read_bits(r, 15);// 位置var len = read_bits(r, 5)+3; // 长度for(var k=0;k<len;k++) { // copy s[s.length]= s[j-off];j++;}}}// UTF8字节数组转为 stringfunction utf8_to_str(s) {var r = [], fc = String.fromCharCode;for(var i=0;i<s.length;i++) {var ch = s[i];if(ch< 0x80)r[r.length] = fc(s[i]);else if(ch < 0xE0) {r[r.length] = fc( ((s[i]&0x1f) << 6) | (s[i+1] & 0x3f));i++;}else if(ch < 0xF0) {r[r.length] = fc( ((s[i] & 0xF) << 12) | ((s[i+1] & 0x3f)<<6) | (s[i+2] & 0x3f));i+=2;}}return r.join('');}s = utf8_to_str(s);return s;}function println(){var m = "";for(var i=0;i<arguments.length;i++)m += arguments[i] + " ";m = m.replace("<","<");m = m.replace(">",">");document.getElementById("msg").innerHTML += m + "<br>";}function compress(){var str = document.getElementById("ta_in").value;var ccc = lz77_c(str);var dstr = lz77_d(ccc);var func_d = "(function(u){var l,h,b,o={},t='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='.split('');for(l=0;l<64;l++){o[t[l]]=l}var a=[],q=1,p=0;for(l=0,h=0;l<u.length;l+=4,h++){a[h]=(o[u.charAt(l)]<<18)|(o[u.charAt(l+1)]<<12)|(o[u.charAt(l+2)]<<6)|(o[u.charAt(l+3)])}function d(i,k){var c,j;if(i.length*24-i[0]-(q*24+p)<k){return -1}j=24-p;if(k<=j){c=(i[q]>>(j-k))&(16777215>>(24-k));p+=k;if(p==24){q++;p=0}return c}else{c=(i[q]&(16777215>>p))<<(k-j);q++;p=0;c|=d(i,k-j);return c}}u=[];h=0;for(;;){var n=d(a,1);if(n<0){break}if(n==0){u[u.length]=d(a,8);h++}else{var e=d(a,15);var m=d(a,5)+3;for(var f=0;f<m;f++){u[u.length]=u[h-e];h++}}}function g(v){var w=[],k=String.fromCharCode;for(var c=0;c<v.length;c++){var j=v[c];if(j<128){w[w.length]=k(v[c])}else{if(j<224){w[w.length]=k(((v[c]&31)<<6)|(v[c+1]&63));c++}else{if(j<240){w[w.length]=k(((v[c]&15)<<12)|((v[c+1]&63)<<6)|(v[c+2]&63));c+=2}}}}return w.join('')}u=g(u);return u})";println(str.length);println(ccc.length);println(str == dstr,str.length,dstr.length);document.getElementById("ta_out").value = "eval("+func_d+"(/""+ccc+"/"));";println(document.getElementById("ta_out").value.length);}