trying to build a djvu decoder

1 files changed, 83 insertions, 0 deletions

diff --git a/djvu.js/zpcoder.js b/djvu.js/zpcoder.js
new file mode 100644
index 0000000..7c31166
--- /dev/null
+++ b/djvu.js/zpcoder.js
@@ -0,0 +1,83 @@
+var ZPDecoder = {
+    create: function(gbs){
+    };
+    decoder: function(ctx){
+    };
+    //table
+    p: new Uint32Array(256);
+    m: new Uint32Array(256);
+    up: new Uint8Array(256);
+    dn: new Uint8Array(256);
+    //machine independent ffz
+    ffzt: new Int8Array(256);
+    ffz: function(x) {
+        //find first zero bit
+        return (x>=0xff00) ? (ffzt[x&0xff]+8) : (ffzt[(x>>8)&0xff]);
+    };
+
+    init: function() {
+        var i, j;
+        for(i = 0; i<256; i++){
+            for(j = i; j&0x80; j<<=1){
+                this.ffzt[i] += 1;
+            }
+        }
+        this.delay = 25;
+        this.scount = 0;
+        this.preload();
+        fence = code;
+        if (code >= 0x8000)
+            fence = 0x7fff;
+    };
+
+    preload: function() {
+        while(this.scount <= 24){
+            if(
+            }
+        }
+    };
+
+    decode_sub: function(ctx, z){
+        // Save bit
+        var bit = ctx & 1;
+        // Avoid interval reversion
+        d = 0x6000 + ((z+a)>>2);
+        if( z > this.d)
+            z = this.d;
+        if( z > this.code) {
+            /* LPS branch */
+            z = 0x10000 - z;
+            this.a = this.a + z;
+            this.code = this.code + z;
+            /* LPS adaptation */
+            ctx = this.dn[ctx];
+            /* LPS renormalization */
+            var shift = ffz(a);
+            this.scount -= shift;
+            this.a = (a<<shift) % 65536;
+            code = (code<<shift) % 65536| ((buffer>>scount) & ((1<<shift)-1));
+            if(this.scount < 16) this.preload();
+            this.fence = this.code;
+            if(this.code >= 0x8000)
+                fence = 0x7fff;
+            return bit ^ 1;
+        }else {
+             /* MPS adaptation */
+            if (this.a >= this.m[ctx])
+                ctx = up[ctx];
+            /* MPS renormalization */
+            this.scount -= 1;
+            a = (unsigned short)(z<<1);
+            this.code = (code<<1) % 65536 | ((buffer>>scount) & 1);
+            if (this.scount<16) this.preload();
+            /* Adjust fence */
+            this.fence = this.code;
+            if (this.code >= 0x8000)
+                this.fence = 0x7fff;
+            return bit;
+        }
+    };
+    IWdecoder: function(){
+        return decode_sub_simple(0, 0x8000 = ((this.a + this.a + this.a) >> 3));
+    }
+}