pdfjs-dist/lib/core/arithmetic_decoder.js

/* Copyright 2017 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
'use strict';

var ArithmeticDecoder = function ArithmeticDecoderClosure() {
  var QeTable = [{
    qe: 0x5601,
    nmps: 1,
    nlps: 1,
    switchFlag: 1
  }, {
    qe: 0x3401,
    nmps: 2,
    nlps: 6,
    switchFlag: 0
  }, {
    qe: 0x1801,
    nmps: 3,
    nlps: 9,
    switchFlag: 0
  }, {
    qe: 0x0AC1,
    nmps: 4,
    nlps: 12,
    switchFlag: 0
  }, {
    qe: 0x0521,
    nmps: 5,
    nlps: 29,
    switchFlag: 0
  }, {
    qe: 0x0221,
    nmps: 38,
    nlps: 33,
    switchFlag: 0
  }, {
    qe: 0x5601,
    nmps: 7,
    nlps: 6,
    switchFlag: 1
  }, {
    qe: 0x5401,
    nmps: 8,
    nlps: 14,
    switchFlag: 0
  }, {
    qe: 0x4801,
    nmps: 9,
    nlps: 14,
    switchFlag: 0
  }, {
    qe: 0x3801,
    nmps: 10,
    nlps: 14,
    switchFlag: 0
  }, {
    qe: 0x3001,
    nmps: 11,
    nlps: 17,
    switchFlag: 0
  }, {
    qe: 0x2401,
    nmps: 12,
    nlps: 18,
    switchFlag: 0
  }, {
    qe: 0x1C01,
    nmps: 13,
    nlps: 20,
    switchFlag: 0
  }, {
    qe: 0x1601,
    nmps: 29,
    nlps: 21,
    switchFlag: 0
  }, {
    qe: 0x5601,
    nmps: 15,
    nlps: 14,
    switchFlag: 1
  }, {
    qe: 0x5401,
    nmps: 16,
    nlps: 14,
    switchFlag: 0
  }, {
    qe: 0x5101,
    nmps: 17,
    nlps: 15,
    switchFlag: 0
  }, {
    qe: 0x4801,
    nmps: 18,
    nlps: 16,
    switchFlag: 0
  }, {
    qe: 0x3801,
    nmps: 19,
    nlps: 17,
    switchFlag: 0
  }, {
    qe: 0x3401,
    nmps: 20,
    nlps: 18,
    switchFlag: 0
  }, {
    qe: 0x3001,
    nmps: 21,
    nlps: 19,
    switchFlag: 0
  }, {
    qe: 0x2801,
    nmps: 22,
    nlps: 19,
    switchFlag: 0
  }, {
    qe: 0x2401,
    nmps: 23,
    nlps: 20,
    switchFlag: 0
  }, {
    qe: 0x2201,
    nmps: 24,
    nlps: 21,
    switchFlag: 0
  }, {
    qe: 0x1C01,
    nmps: 25,
    nlps: 22,
    switchFlag: 0
  }, {
    qe: 0x1801,
    nmps: 26,
    nlps: 23,
    switchFlag: 0
  }, {
    qe: 0x1601,
    nmps: 27,
    nlps: 24,
    switchFlag: 0
  }, {
    qe: 0x1401,
    nmps: 28,
    nlps: 25,
    switchFlag: 0
  }, {
    qe: 0x1201,
    nmps: 29,
    nlps: 26,
    switchFlag: 0
  }, {
    qe: 0x1101,
    nmps: 30,
    nlps: 27,
    switchFlag: 0
  }, {
    qe: 0x0AC1,
    nmps: 31,
    nlps: 28,
    switchFlag: 0
  }, {
    qe: 0x09C1,
    nmps: 32,
    nlps: 29,
    switchFlag: 0
  }, {
    qe: 0x08A1,
    nmps: 33,
    nlps: 30,
    switchFlag: 0
  }, {
    qe: 0x0521,
    nmps: 34,
    nlps: 31,
    switchFlag: 0
  }, {
    qe: 0x0441,
    nmps: 35,
    nlps: 32,
    switchFlag: 0
  }, {
    qe: 0x02A1,
    nmps: 36,
    nlps: 33,
    switchFlag: 0
  }, {
    qe: 0x0221,
    nmps: 37,
    nlps: 34,
    switchFlag: 0
  }, {
    qe: 0x0141,
    nmps: 38,
    nlps: 35,
    switchFlag: 0
  }, {
    qe: 0x0111,
    nmps: 39,
    nlps: 36,
    switchFlag: 0
  }, {
    qe: 0x0085,
    nmps: 40,
    nlps: 37,
    switchFlag: 0
  }, {
    qe: 0x0049,
    nmps: 41,
    nlps: 38,
    switchFlag: 0
  }, {
    qe: 0x0025,
    nmps: 42,
    nlps: 39,
    switchFlag: 0
  }, {
    qe: 0x0015,
    nmps: 43,
    nlps: 40,
    switchFlag: 0
  }, {
    qe: 0x0009,
    nmps: 44,
    nlps: 41,
    switchFlag: 0
  }, {
    qe: 0x0005,
    nmps: 45,
    nlps: 42,
    switchFlag: 0
  }, {
    qe: 0x0001,
    nmps: 45,
    nlps: 43,
    switchFlag: 0
  }, {
    qe: 0x5601,
    nmps: 46,
    nlps: 46,
    switchFlag: 0
  }];
  function ArithmeticDecoder(data, start, end) {
    this.data = data;
    this.bp = start;
    this.dataEnd = end;
    this.chigh = data[start];
    this.clow = 0;
    this.byteIn();
    this.chigh = this.chigh << 7 & 0xFFFF | this.clow >> 9 & 0x7F;
    this.clow = this.clow << 7 & 0xFFFF;
    this.ct -= 7;
    this.a = 0x8000;
  }
  ArithmeticDecoder.prototype = {
    byteIn: function ArithmeticDecoder_byteIn() {
      var data = this.data;
      var bp = this.bp;
      if (data[bp] === 0xFF) {
        var b1 = data[bp + 1];
        if (b1 > 0x8F) {
          this.clow += 0xFF00;
          this.ct = 8;
        } else {
          bp++;
          this.clow += data[bp] << 9;
          this.ct = 7;
          this.bp = bp;
        }
      } else {
        bp++;
        this.clow += bp < this.dataEnd ? data[bp] << 8 : 0xFF00;
        this.ct = 8;
        this.bp = bp;
      }
      if (this.clow > 0xFFFF) {
        this.chigh += this.clow >> 16;
        this.clow &= 0xFFFF;
      }
    },
    readBit: function ArithmeticDecoder_readBit(contexts, pos) {
      var cx_index = contexts[pos] >> 1,
          cx_mps = contexts[pos] & 1;
      var qeTableIcx = QeTable[cx_index];
      var qeIcx = qeTableIcx.qe;
      var d;
      var a = this.a - qeIcx;
      if (this.chigh < qeIcx) {
        if (a < qeIcx) {
          a = qeIcx;
          d = cx_mps;
          cx_index = qeTableIcx.nmps;
        } else {
          a = qeIcx;
          d = 1 ^ cx_mps;
          if (qeTableIcx.switchFlag === 1) {
            cx_mps = d;
          }
          cx_index = qeTableIcx.nlps;
        }
      } else {
        this.chigh -= qeIcx;
        if ((a & 0x8000) !== 0) {
          this.a = a;
          return cx_mps;
        }
        if (a < qeIcx) {
          d = 1 ^ cx_mps;
          if (qeTableIcx.switchFlag === 1) {
            cx_mps = d;
          }
          cx_index = qeTableIcx.nlps;
        } else {
          d = cx_mps;
          cx_index = qeTableIcx.nmps;
        }
      }
      do {
        if (this.ct === 0) {
          this.byteIn();
        }
        a <<= 1;
        this.chigh = this.chigh << 1 & 0xFFFF | this.clow >> 15 & 1;
        this.clow = this.clow << 1 & 0xFFFF;
        this.ct--;
      } while ((a & 0x8000) === 0);
      this.a = a;
      contexts[pos] = cx_index << 1 | cx_mps;
      return d;
    }
  };
  return ArithmeticDecoder;
}();
exports.ArithmeticDecoder = ArithmeticDecoder;