pdf.js/src/core/function.js

/* Copyright 2012 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.
 */
/* globals PostScriptLexer, PostScriptParser, error, info, isArray, isBool,
           isDict, isStream */

'use strict';

var PDFFunction = (function PDFFunctionClosure() {
  var CONSTRUCT_SAMPLED = 0;
  var CONSTRUCT_INTERPOLATED = 2;
  var CONSTRUCT_STICHED = 3;
  var CONSTRUCT_POSTSCRIPT = 4;

  return {
    getSampleArray: function PDFFunction_getSampleArray(size, outputSize, bps,
                                                       str) {
      var i, ii;
      var length = 1;
      for (i = 0, ii = size.length; i < ii; i++) {
        length *= size[i];
      }
      length *= outputSize;

      var array = new Array(length);
      var codeSize = 0;
      var codeBuf = 0;
      // 32 is a valid bps so shifting won't work
      var sampleMul = 1.0 / (Math.pow(2.0, bps) - 1);

      var strBytes = str.getBytes((length * bps + 7) / 8);
      var strIdx = 0;
      for (i = 0; i < length; i++) {
        while (codeSize < bps) {
          codeBuf <<= 8;
          codeBuf |= strBytes[strIdx++];
          codeSize += 8;
        }
        codeSize -= bps;
        array[i] = (codeBuf >> codeSize) * sampleMul;
        codeBuf &= (1 << codeSize) - 1;
      }
      return array;
    },

    getIR: function PDFFunction_getIR(xref, fn) {
      var dict = fn.dict;
      if (!dict) {
        dict = fn;
      }

      var types = [this.constructSampled,
                   null,
                   this.constructInterpolated,
                   this.constructStiched,
                   this.constructPostScript];

      var typeNum = dict.get('FunctionType');
      var typeFn = types[typeNum];
      if (!typeFn) {
        error('Unknown type of function');
      }

      return typeFn.call(this, fn, dict, xref);
    },

    fromIR: function PDFFunction_fromIR(IR) {
      var type = IR[0];
      switch (type) {
        case CONSTRUCT_SAMPLED:
          return this.constructSampledFromIR(IR);
        case CONSTRUCT_INTERPOLATED:
          return this.constructInterpolatedFromIR(IR);
        case CONSTRUCT_STICHED:
          return this.constructStichedFromIR(IR);
        //case CONSTRUCT_POSTSCRIPT:
        default:
          return this.constructPostScriptFromIR(IR);
      }
    },

    parse: function PDFFunction_parse(xref, fn) {
      var IR = this.getIR(xref, fn);
      return this.fromIR(IR);
    },

    parseArray: function PDFFunction_parseArray(xref, fnObj) {
      if (!isArray(fnObj)) {
        // not an array -- parsing as regular function
        return this.parse(xref, fnObj);
      }

      var fnArray = [];
      for (var j = 0, jj = fnObj.length; j < jj; j++) {
        var obj = xref.fetchIfRef(fnObj[j]);
        fnArray.push(PDFFunction.parse(xref, obj));
      }
      return function (src, srcOffset, dest, destOffset) {
        for (var i = 0, ii = fnArray.length; i < ii; i++) {
          fnArray[i](src, srcOffset, dest, destOffset + i);
        }
      };
    },

    constructSampled: function PDFFunction_constructSampled(str, dict) {
      function toMultiArray(arr) {
        var inputLength = arr.length;
        var out = [];
        var index = 0;
        for (var i = 0; i < inputLength; i += 2) {
          out[index] = [arr[i], arr[i + 1]];
          ++index;
        }
        return out;
      }
      var domain = dict.get('Domain');
      var range = dict.get('Range');

      if (!domain || !range) {
        error('No domain or range');
      }

      var inputSize = domain.length / 2;
      var outputSize = range.length / 2;

      domain = toMultiArray(domain);
      range = toMultiArray(range);

      var size = dict.get('Size');
      var bps = dict.get('BitsPerSample');
      var order = dict.get('Order') || 1;
      if (order !== 1) {
        // No description how cubic spline interpolation works in PDF32000:2008
        // As in poppler, ignoring order, linear interpolation may work as good
        info('No support for cubic spline interpolation: ' + order);
      }

      var encode = dict.get('Encode');
      if (!encode) {
        encode = [];
        for (var i = 0; i < inputSize; ++i) {
          encode.push(0);
          encode.push(size[i] - 1);
        }
      }
      encode = toMultiArray(encode);

      var decode = dict.get('Decode');
      if (!decode) {
        decode = range;
      } else {
        decode = toMultiArray(decode);
      }

      var samples = this.getSampleArray(size, outputSize, bps, str);

      return [
        CONSTRUCT_SAMPLED, inputSize, domain, encode, decode, samples, size,
        outputSize, Math.pow(2, bps) - 1, range
      ];
    },

    constructSampledFromIR: function PDFFunction_constructSampledFromIR(IR) {
      // See chapter 3, page 109 of the PDF reference
      function interpolate(x, xmin, xmax, ymin, ymax) {
        return ymin + ((x - xmin) * ((ymax - ymin) / (xmax - xmin)));
      }

      return function constructSampledFromIRResult(src, srcOffset,
                                                   dest, destOffset) {
        // See chapter 3, page 110 of the PDF reference.
        var m = IR[1];
        var domain = IR[2];
        var encode = IR[3];
        var decode = IR[4];
        var samples = IR[5];
        var size = IR[6];
        var n = IR[7];
        //var mask = IR[8];
        var range = IR[9];

        // Building the cube vertices: its part and sample index
        // http://rjwagner49.com/Mathematics/Interpolation.pdf
        var cubeVertices = 1 << m;
        var cubeN = new Float64Array(cubeVertices);
        var cubeVertex = new Uint32Array(cubeVertices);
        var i, j;
        for (j = 0; j < cubeVertices; j++) {
          cubeN[j] = 1;
        }

        var k = n, pos = 1;
        // Map x_i to y_j for 0 <= i < m using the sampled function.
        for (i = 0; i < m; ++i) {
          // x_i' = min(max(x_i, Domain_2i), Domain_2i+1)
          var domain_2i = domain[i][0];
          var domain_2i_1 = domain[i][1];
          var xi = Math.min(Math.max(src[srcOffset +i], domain_2i),
                            domain_2i_1);

          // e_i = Interpolate(x_i', Domain_2i, Domain_2i+1,
          //                   Encode_2i, Encode_2i+1)
          var e = interpolate(xi, domain_2i, domain_2i_1,
                              encode[i][0], encode[i][1]);

          // e_i' = min(max(e_i, 0), Size_i - 1)
          var size_i = size[i];
          e = Math.min(Math.max(e, 0), size_i - 1);

          // Adjusting the cube: N and vertex sample index
          var e0 = e < size_i - 1 ? Math.floor(e) : e - 1; // e1 = e0 + 1;
          var n0 = e0 + 1 - e; // (e1 - e) / (e1 - e0);
          var n1 = e - e0; // (e - e0) / (e1 - e0);
          var offset0 = e0 * k;
          var offset1 = offset0 + k; // e1 * k
          for (j = 0; j < cubeVertices; j++) {
            if (j & pos) {
              cubeN[j] *= n1;
              cubeVertex[j] += offset1;
            } else {
              cubeN[j] *= n0;
              cubeVertex[j] += offset0;
            }
          }

          k *= size_i;
          pos <<= 1;
        }

        for (j = 0; j < n; ++j) {
          // Sum all cube vertices' samples portions
          var rj = 0;
          for (i = 0; i < cubeVertices; i++) {
            rj += samples[cubeVertex[i] + j] * cubeN[i];
          }

          // r_j' = Interpolate(r_j, 0, 2^BitsPerSample - 1,
          //                    Decode_2j, Decode_2j+1)
          rj = interpolate(rj, 0, 1, decode[j][0], decode[j][1]);

          // y_j = min(max(r_j, range_2j), range_2j+1)
          dest[destOffset + j] = Math.min(Math.max(rj, range[j][0]),
                                          range[j][1]);
        }
      };
    },

    constructInterpolated: function PDFFunction_constructInterpolated(str,
                                                                      dict) {
      var c0 = dict.get('C0') || [0];
      var c1 = dict.get('C1') || [1];
      var n = dict.get('N');

      if (!isArray(c0) || !isArray(c1)) {
        error('Illegal dictionary for interpolated function');
      }

      var length = c0.length;
      var diff = [];
      for (var i = 0; i < length; ++i) {
        diff.push(c1[i] - c0[i]);
      }

      return [CONSTRUCT_INTERPOLATED, c0, diff, n];
    },

    constructInterpolatedFromIR:
      function PDFFunction_constructInterpolatedFromIR(IR) {
      var c0 = IR[1];
      var diff = IR[2];
      var n = IR[3];

      var length = diff.length;

      return function constructInterpolatedFromIRResult(src, srcOffset,
                                                        dest, destOffset) {
        var x = n === 1 ? src[srcOffset] : Math.pow(src[srcOffset], n);

        for (var j = 0; j < length; ++j) {
          dest[destOffset + j] = c0[j] + (x * diff[j]);
        }
      };
    },

    constructStiched: function PDFFunction_constructStiched(fn, dict, xref) {
      var domain = dict.get('Domain');

      if (!domain) {
        error('No domain');
      }

      var inputSize = domain.length / 2;
      if (inputSize !== 1) {
        error('Bad domain for stiched function');
      }

      var fnRefs = dict.get('Functions');
      var fns = [];
      for (var i = 0, ii = fnRefs.length; i < ii; ++i) {
        fns.push(PDFFunction.getIR(xref, xref.fetchIfRef(fnRefs[i])));
      }

      var bounds = dict.get('Bounds');
      var encode = dict.get('Encode');

      return [CONSTRUCT_STICHED, domain, bounds, encode, fns];
    },

    constructStichedFromIR: function PDFFunction_constructStichedFromIR(IR) {
      var domain = IR[1];
      var bounds = IR[2];
      var encode = IR[3];
      var fnsIR = IR[4];
      var fns = [];
      var tmpBuf = new Float32Array(1);

      for (var i = 0, ii = fnsIR.length; i < ii; i++) {
        fns.push(PDFFunction.fromIR(fnsIR[i]));
      }

      return function constructStichedFromIRResult(src, srcOffset,
                                                   dest, destOffset) {
        var clip = function constructStichedFromIRClip(v, min, max) {
          if (v > max) {
            v = max;
          } else if (v < min) {
            v = min;
          }
          return v;
        };

        // clip to domain
        var v = clip(src[srcOffset], domain[0], domain[1]);
        // calulate which bound the value is in
        for (var i = 0, ii = bounds.length; i < ii; ++i) {
          if (v < bounds[i]) {
            break;
          }
        }

        // encode value into domain of function
        var dmin = domain[0];
        if (i > 0) {
          dmin = bounds[i - 1];
        }
        var dmax = domain[1];
        if (i < bounds.length) {
          dmax = bounds[i];
        }

        var rmin = encode[2 * i];
        var rmax = encode[2 * i + 1];

        // Prevent the value from becoming NaN as a result
        // of division by zero (fixes issue6113.pdf).
        tmpBuf[0] = dmin === dmax ? rmin :
                    rmin + (v - dmin) * (rmax - rmin) / (dmax - dmin);

        // call the appropriate function
        fns[i](tmpBuf, 0, dest, destOffset);
      };
    },

    constructPostScript: function PDFFunction_constructPostScript(fn, dict,
                                                                  xref) {
      var domain = dict.get('Domain');
      var range = dict.get('Range');

      if (!domain) {
        error('No domain.');
      }

      if (!range) {
        error('No range.');
      }

      var lexer = new PostScriptLexer(fn);
      var parser = new PostScriptParser(lexer);
      var code = parser.parse();

      return [CONSTRUCT_POSTSCRIPT, domain, range, code];
    },

    constructPostScriptFromIR: function PDFFunction_constructPostScriptFromIR(
                                          IR) {
      var domain = IR[1];
      var range = IR[2];
      var code = IR[3];

      var compiled = (new PostScriptCompiler()).compile(code, domain, range);
      if (compiled) {
        // Compiled function consists of simple expressions such as addition,
        // subtraction, Math.max, and also contains 'var' and 'return'
        // statements. See the generation in the PostScriptCompiler below.
        /*jshint -W054 */
        return new Function('src', 'srcOffset', 'dest', 'destOffset', compiled);
      }

      info('Unable to compile PS function');

      var numOutputs = range.length >> 1;
      var numInputs = domain.length >> 1;
      var evaluator = new PostScriptEvaluator(code);
      // Cache the values for a big speed up, the cache size is limited though
      // since the number of possible values can be huge from a PS function.
      var cache = {};
      // The MAX_CACHE_SIZE is set to ~4x the maximum number of distinct values
      // seen in our tests.
      var MAX_CACHE_SIZE = 2048 * 4;
      var cache_available = MAX_CACHE_SIZE;
      var tmpBuf = new Float32Array(numInputs);

      return function constructPostScriptFromIRResult(src, srcOffset,
                                                      dest, destOffset) {
        var i, value;
        var key = '';
        var input = tmpBuf;
        for (i = 0; i < numInputs; i++) {
          value = src[srcOffset + i];
          input[i] = value;
          key += value + '_';
        }

        var cachedValue = cache[key];
        if (cachedValue !== undefined) {
          dest.set(cachedValue, destOffset);
          return;
        }

        var output = new Float32Array(numOutputs);
        var stack = evaluator.execute(input);
        var stackIndex = stack.length - numOutputs;
        for (i = 0; i < numOutputs; i++) {
          value = stack[stackIndex + i];
          var bound = range[i * 2];
          if (value < bound) {
            value = bound;
          } else {
            bound = range[i * 2 +1];
            if (value > bound) {
              value = bound;
            }
          }
          output[i] = value;
        }
        if (cache_available > 0) {
          cache_available--;
          cache[key] = output;
        }
        dest.set(output, destOffset);
      };
    }
  };
})();

function isPDFFunction(v) {
  var fnDict;
  if (typeof v !== 'object') {
    return false;
  } else if (isDict(v)) {
    fnDict = v;
  } else if (isStream(v)) {
    fnDict = v.dict;
  } else {
    return false;
  }
  return fnDict.has('FunctionType');
}

var PostScriptStack = (function PostScriptStackClosure() {
  var MAX_STACK_SIZE = 100;
  function PostScriptStack(initialStack) {
    this.stack = !initialStack ? [] :
                 Array.prototype.slice.call(initialStack, 0);
  }

  PostScriptStack.prototype = {
    push: function PostScriptStack_push(value) {
      if (this.stack.length >= MAX_STACK_SIZE) {
        error('PostScript function stack overflow.');
      }
      this.stack.push(value);
    },
    pop: function PostScriptStack_pop() {
      if (this.stack.length <= 0) {
        error('PostScript function stack underflow.');
      }
      return this.stack.pop();
    },
    copy: function PostScriptStack_copy(n) {
      if (this.stack.length + n >= MAX_STACK_SIZE) {
        error('PostScript function stack overflow.');
      }
      var stack = this.stack;
      for (var i = stack.length - n, j = n - 1; j >= 0; j--, i++) {
        stack.push(stack[i]);
      }
    },
    index: function PostScriptStack_index(n) {
      this.push(this.stack[this.stack.length - n - 1]);
    },
    // rotate the last n stack elements p times
    roll: function PostScriptStack_roll(n, p) {
      var stack = this.stack;
      var l = stack.length - n;
      var r = stack.length - 1, c = l + (p - Math.floor(p / n) * n), i, j, t;
      for (i = l, j = r; i < j; i++, j--) {
        t = stack[i]; stack[i] = stack[j]; stack[j] = t;
      }
      for (i = l, j = c - 1; i < j; i++, j--) {
        t = stack[i]; stack[i] = stack[j]; stack[j] = t;
      }
      for (i = c, j = r; i < j; i++, j--) {
        t = stack[i]; stack[i] = stack[j]; stack[j] = t;
      }
    }
  };
  return PostScriptStack;
})();
var PostScriptEvaluator = (function PostScriptEvaluatorClosure() {
  function PostScriptEvaluator(operators) {
    this.operators = operators;
  }
  PostScriptEvaluator.prototype = {
    execute: function PostScriptEvaluator_execute(initialStack) {
      var stack = new PostScriptStack(initialStack);
      var counter = 0;
      var operators = this.operators;
      var length = operators.length;
      var operator, a, b;
      while (counter < length) {
        operator = operators[counter++];
        if (typeof operator === 'number') {
          // Operator is really an operand and should be pushed to the stack.
          stack.push(operator);
          continue;
        }
        switch (operator) {
          // non standard ps operators
          case 'jz': // jump if false
            b = stack.pop();
            a = stack.pop();
            if (!a) {
              counter = b;
            }
            break;
          case 'j': // jump
            a = stack.pop();
            counter = a;
            break;

          // all ps operators in alphabetical order (excluding if/ifelse)
          case 'abs':
            a = stack.pop();
            stack.push(Math.abs(a));
            break;
          case 'add':
            b = stack.pop();
            a = stack.pop();
            stack.push(a + b);
            break;
          case 'and':
            b = stack.pop();
            a = stack.pop();
            if (isBool(a) && isBool(b)) {
              stack.push(a && b);
            } else {
              stack.push(a & b);
            }
            break;
          case 'atan':
            a = stack.pop();
            stack.push(Math.atan(a));
            break;
          case 'bitshift':
            b = stack.pop();
            a = stack.pop();
            if (a > 0) {
              stack.push(a << b);
            } else {
              stack.push(a >> b);
            }
            break;
          case 'ceiling':
            a = stack.pop();
            stack.push(Math.ceil(a));
            break;
          case 'copy':
            a = stack.pop();
            stack.copy(a);
            break;
          case 'cos':
            a = stack.pop();
            stack.push(Math.cos(a));
            break;
          case 'cvi':
            a = stack.pop() | 0;
            stack.push(a);
            break;
          case 'cvr':
            // noop
            break;
          case 'div':
            b = stack.pop();
            a = stack.pop();
            stack.push(a / b);
            break;
          case 'dup':
            stack.copy(1);
            break;
          case 'eq':
            b = stack.pop();
            a = stack.pop();
            stack.push(a === b);
            break;
          case 'exch':
            stack.roll(2, 1);
            break;
          case 'exp':
            b = stack.pop();
            a = stack.pop();
            stack.push(Math.pow(a, b));
            break;
          case 'false':
            stack.push(false);
            break;
          case 'floor':
            a = stack.pop();
            stack.push(Math.floor(a));
            break;
          case 'ge':
            b = stack.pop();
            a = stack.pop();
            stack.push(a >= b);
            break;
          case 'gt':
            b = stack.pop();
            a = stack.pop();
            stack.push(a > b);
            break;
          case 'idiv':
            b = stack.pop();
            a = stack.pop();
            stack.push((a / b) | 0);
            break;
          case 'index':
            a = stack.pop();
            stack.index(a);
            break;
          case 'le':
            b = stack.pop();
            a = stack.pop();
            stack.push(a <= b);
            break;
          case 'ln':
            a = stack.pop();
            stack.push(Math.log(a));
            break;
          case 'log':
            a = stack.pop();
            stack.push(Math.log(a) / Math.LN10);
            break;
          case 'lt':
            b = stack.pop();
            a = stack.pop();
            stack.push(a < b);
            break;
          case 'mod':
            b = stack.pop();
            a = stack.pop();
            stack.push(a % b);
            break;
          case 'mul':
            b = stack.pop();
            a = stack.pop();
            stack.push(a * b);
            break;
          case 'ne':
            b = stack.pop();
            a = stack.pop();
            stack.push(a !== b);
            break;
          case 'neg':
            a = stack.pop();
            stack.push(-a);
            break;
          case 'not':
            a = stack.pop();
            if (isBool(a)) {
              stack.push(!a);
            } else {
              stack.push(~a);
            }
            break;
          case 'or':
            b = stack.pop();
            a = stack.pop();
            if (isBool(a) && isBool(b)) {
              stack.push(a || b);
            } else {
              stack.push(a | b);
            }
            break;
          case 'pop':
            stack.pop();
            break;
          case 'roll':
            b = stack.pop();
            a = stack.pop();
            stack.roll(a, b);
            break;
          case 'round':
            a = stack.pop();
            stack.push(Math.round(a));
            break;
          case 'sin':
            a = stack.pop();
            stack.push(Math.sin(a));
            break;
          case 'sqrt':
            a = stack.pop();
            stack.push(Math.sqrt(a));
            break;
          case 'sub':
            b = stack.pop();
            a = stack.pop();
            stack.push(a - b);
            break;
          case 'true':
            stack.push(true);
            break;
          case 'truncate':
            a = stack.pop();
            a = a < 0 ? Math.ceil(a) : Math.floor(a);
            stack.push(a);
            break;
          case 'xor':
            b = stack.pop();
            a = stack.pop();
            if (isBool(a) && isBool(b)) {
              stack.push(a !== b);
            } else {
              stack.push(a ^ b);
            }
            break;
          default:
            error('Unknown operator ' + operator);
            break;
        }
      }
      return stack.stack;
    }
  };
  return PostScriptEvaluator;
})();

// Most of the PDFs functions consist of simple operations such as:
//   roll, exch, sub, cvr, pop, index, dup, mul, if, gt, add.
//
// We can compile most of such programs, and at the same moment, we can
// optimize some expressions using basic math properties. Keeping track of
// min/max values will allow us to avoid extra Math.min/Math.max calls.
var PostScriptCompiler = (function PostScriptCompilerClosure() {
  function AstNode(type) {
    this.type = type;
  }
  AstNode.prototype.visit = function (visitor) {
    throw new Error('abstract method');
  };

  function AstArgument(index, min, max) {
    AstNode.call(this, 'args');
    this.index = index;
    this.min = min;
    this.max = max;
  }
  AstArgument.prototype = Object.create(AstNode.prototype);
  AstArgument.prototype.visit = function (visitor) {
    visitor.visitArgument(this);
  };

  function AstLiteral(number) {
    AstNode.call(this, 'literal');
    this.number = number;
    this.min = number;
    this.max = number;
  }
  AstLiteral.prototype = Object.create(AstNode.prototype);
  AstLiteral.prototype.visit = function (visitor) {
    visitor.visitLiteral(this);
  };

  function AstBinaryOperation(op, arg1, arg2, min, max) {
    AstNode.call(this, 'binary');
    this.op = op;
    this.arg1 = arg1;
    this.arg2 = arg2;
    this.min = min;
    this.max = max;
  }
  AstBinaryOperation.prototype = Object.create(AstNode.prototype);
  AstBinaryOperation.prototype.visit = function (visitor) {
    visitor.visitBinaryOperation(this);
  };

  function AstMin(arg, max) {
    AstNode.call(this, 'max');
    this.arg = arg;
    this.min = arg.min;
    this.max = max;
  }
  AstMin.prototype = Object.create(AstNode.prototype);
  AstMin.prototype.visit = function (visitor) {
    visitor.visitMin(this);
  };

  function AstVariable(index, min, max) {
    AstNode.call(this, 'var');
    this.index = index;
    this.min = min;
    this.max = max;
  }
  AstVariable.prototype = Object.create(AstNode.prototype);
  AstVariable.prototype.visit = function (visitor) {
    visitor.visitVariable(this);
  };

  function AstVariableDefinition(variable, arg) {
    AstNode.call(this, 'definition');
    this.variable = variable;
    this.arg = arg;
  }
  AstVariableDefinition.prototype = Object.create(AstNode.prototype);
  AstVariableDefinition.prototype.visit = function (visitor) {
    visitor.visitVariableDefinition(this);
  };

  function ExpressionBuilderVisitor() {
    this.parts = [];
  }
  ExpressionBuilderVisitor.prototype = {
    visitArgument: function (arg) {
      this.parts.push('Math.max(', arg.min, ', Math.min(',
                      arg.max, ', src[srcOffset + ', arg.index, ']))');
    },
    visitVariable: function (variable) {
      this.parts.push('v', variable.index);
    },
    visitLiteral: function (literal) {
      this.parts.push(literal.number);
    },
    visitBinaryOperation: function (operation) {
      this.parts.push('(');
      operation.arg1.visit(this);
      this.parts.push(' ', operation.op, ' ');
      operation.arg2.visit(this);
      this.parts.push(')');
    },
    visitVariableDefinition: function (definition) {
      this.parts.push('var ');
      definition.variable.visit(this);
      this.parts.push(' = ');
      definition.arg.visit(this);
      this.parts.push(';');
    },
    visitMin: function (max) {
      this.parts.push('Math.min(');
      max.arg.visit(this);
      this.parts.push(', ', max.max, ')');
    },
    toString: function () {
      return this.parts.join('');
    }
  };

  function buildAddOperation(num1, num2) {
    if (num2.type === 'literal' && num2.number === 0) {
      // optimization: second operand is 0
      return num1;
    }
    if (num1.type === 'literal' && num1.number === 0) {
      // optimization: first operand is 0
      return num2;
    }
    if (num2.type === 'literal' && num1.type === 'literal') {
      // optimization: operands operand are literals
      return new AstLiteral(num1.number + num2.number);
    }
    return new AstBinaryOperation('+', num1, num2,
                                  num1.min + num2.min, num1.max + num2.max);
  }

  function buildMulOperation(num1, num2) {
    if (num2.type === 'literal') {
      // optimization: second operands is a literal...
      if (num2.number === 0) {
        return new AstLiteral(0); // and it's 0
      } else if (num2.number === 1) {
        return num1; // and it's 1
      } else if (num1.type === 'literal') {
        // ... and first operands is a literal too
        return new AstLiteral(num1.number * num2.number);
      }
    }
    if (num1.type === 'literal') {
      // optimization: first operands is a literal...
      if (num1.number === 0) {
        return new AstLiteral(0); // and it's 0
      } else if (num1.number === 1) {
        return num2; // and it's 1
      }
    }
    var min = Math.min(num1.min * num2.min, num1.min * num2.max,
                       num1.max * num2.min, num1.max * num2.max);
    var max = Math.max(num1.min * num2.min, num1.min * num2.max,
                       num1.max * num2.min, num1.max * num2.max);
    return new AstBinaryOperation('*', num1, num2, min, max);
  }

  function buildSubOperation(num1, num2) {
    if (num2.type === 'literal') {
      // optimization: second operands is a literal...
      if (num2.number === 0) {
        return num1; // ... and it's 0
      } else if (num1.type === 'literal') {
        // ... and first operands is a literal too
        return new AstLiteral(num1.number - num2.number);
      }
    }
    if (num2.type === 'binary' && num2.op === '-' &&
      num1.type === 'literal' && num1.number === 1 &&
      num2.arg1.type === 'literal' && num2.arg1.number === 1) {
      // optimization for case: 1 - (1 - x)
      return num2.arg2;
    }
    return new AstBinaryOperation('-', num1, num2,
                                  num1.min - num2.max, num1.max - num2.min);
  }

  function buildMinOperation(num1, max) {
    if (num1.min >= max) {
      // optimization: num1 min value is not less than required max
      return new AstLiteral(max); // just returning max
    } else if (num1.max <= max) {
      // optimization: num1 max value is not greater than required max
      return num1; // just returning an argument
    }
    return new AstMin(num1, max);
  }

  function PostScriptCompiler() {}
  PostScriptCompiler.prototype = {
    compile: function PostScriptCompiler_compile(code, domain, range) {
      var stack = [];
      var i, ii;
      var instructions = [];
      var inputSize = domain.length >> 1, outputSize = range.length >> 1;
      var lastRegister = 0;
      var n, j, min, max;
      var num1, num2, ast1, ast2, tmpVar, item;
      for (i = 0; i < inputSize; i++) {
        stack.push(new AstArgument(i, domain[i * 2], domain[i * 2 + 1]));
      }

      for (i = 0, ii = code.length; i < ii; i++) {
        item = code[i];
        if (typeof item === 'number') {
          stack.push(new AstLiteral(item));
          continue;
        }

        switch (item) {
          case 'add':
            if (stack.length < 2) {
              return null;
            }
            num2 = stack.pop();
            num1 = stack.pop();
            stack.push(buildAddOperation(num1, num2));
            break;
          case 'cvr':
            if (stack.length < 1) {
              return null;
            }
            break;
          case 'mul':
            if (stack.length < 2) {
              return null;
            }
            num2 = stack.pop();
            num1 = stack.pop();
            stack.push(buildMulOperation(num1, num2));
            break;
          case 'sub':
            if (stack.length < 2) {
              return null;
            }
            num2 = stack.pop();
            num1 = stack.pop();
            stack.push(buildSubOperation(num1, num2));
            break;
          case 'exch':
            if (stack.length < 2) {
              return null;
            }
            ast1 = stack.pop(); ast2 = stack.pop();
            stack.push(ast1, ast2);
            break;
          case 'pop':
            if (stack.length < 1) {
              return null;
            }
            stack.pop();
            break;
          case 'index':
            if (stack.length < 1) {
              return null;
            }
            num1 = stack.pop();
            if (num1.type !== 'literal') {
              return null;
            }
            n = num1.number;
            if (n < 0 || (n|0) !== n || stack.length < n) {
              return null;
            }
            ast1 = stack[stack.length - n - 1];
            if (ast1.type === 'literal' || ast1.type === 'var') {
              stack.push(ast1);
              break;
            }
            tmpVar = new AstVariable(lastRegister++, ast1.min, ast1.max);
            stack[stack.length - n - 1] = tmpVar;
            stack.push(tmpVar);
            instructions.push(new AstVariableDefinition(tmpVar, ast1));
            break;
          case 'dup':
            if (stack.length < 1) {
              return null;
            }
            if (typeof code[i + 1] === 'number' && code[i + 2] === 'gt' &&
                code[i + 3] === i + 7 && code[i + 4] === 'jz' &&
                code[i + 5] === 'pop' && code[i + 6] === code[i + 1]) {
              // special case of the commands sequence for the min operation
              num1 = stack.pop();
              stack.push(buildMinOperation(num1, code[i + 1]));
              i += 6;
              break;
            }
            ast1 = stack[stack.length - 1];
            if (ast1.type === 'literal' || ast1.type === 'var') {
              // we don't have to save into intermediate variable a literal or
              // variable.
              stack.push(ast1);
              break;
            }
            tmpVar = new AstVariable(lastRegister++, ast1.min, ast1.max);
            stack[stack.length - 1] = tmpVar;
            stack.push(tmpVar);
            instructions.push(new AstVariableDefinition(tmpVar, ast1));
            break;
          case 'roll':
            if (stack.length < 2) {
              return null;
            }
            num2 = stack.pop();
            num1 = stack.pop();
            if (num2.type !== 'literal' || num1.type !== 'literal') {
              // both roll operands must be numbers
              return null;
            }
            j = num2.number;
            n = num1.number;
            if (n <= 0 || (n|0) !== n || (j|0) !== j || stack.length < n) {
              // ... and integers
              return null;
            }
            j = ((j % n) + n) % n;
            if (j === 0) {
              break; // just skipping -- there are nothing to rotate
            }
            Array.prototype.push.apply(stack,
                                       stack.splice(stack.length - n, n - j));
            break;
          default:
            return null; // unsupported operator
        }
      }

      if (stack.length !== outputSize) {
        return null;
      }

      var result = [];
      instructions.forEach(function (instruction) {
        var statementBuilder = new ExpressionBuilderVisitor();
        instruction.visit(statementBuilder);
        result.push(statementBuilder.toString());
      });
      stack.forEach(function (expr, i) {
        var statementBuilder = new ExpressionBuilderVisitor();
        expr.visit(statementBuilder);
        var min = range[i * 2], max = range[i * 2 + 1];
        var out = [statementBuilder.toString()];
        if (min > expr.min) {
          out.unshift('Math.max(', min, ', ');
          out.push(')');
        }
        if (max < expr.max) {
          out.unshift('Math.min(', max, ', ');
          out.push(')');
        }
        out.unshift('dest[destOffset + ', i, '] = ');
        out.push(';');
        result.push(out.join(''));
      });
      return result.join('\n');
    }
  };

  return PostScriptCompiler;
})();