runtime.js

// Copyright 2010 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

//"use strict";

var Compiletime = {
  isPointerType: isPointerType,
  isStructType: isStructType,

  isNumberType: function(type) {
    return type in Compiletime.INT_TYPES || type in Compiletime.FLOAT_TYPES;
  },

  INT_TYPES: set('i1', 'i8', 'i16', 'i32', 'i64'),
  FLOAT_TYPES: set('float', 'double'),
};

// code used both at compile time and runtime is defined here, then put on
// the Runtime object for compile time and support.js for the generated code

function getNativeTypeSize(type) {
  switch (type) {
    case 'i1': case 'i8': return 1;
    case 'i16': return 2;
    case 'i32': return 4;
    case 'i64': return 8;
    case 'float': return 4;
    case 'double': return 8;
    default: {
      if (type[type.length-1] === '*') {
        return 4; // A pointer
      } else if (type[0] === 'i') {
        var bits = parseInt(type.substr(1));
        assert(bits % 8 === 0, 'getNativeTypeSize invalid bits ' + bits + ', type ' + type);
        return bits / 8;
      } else {
        return 0;
      }
    }
  }
}

function alignMemory(size, factor) {
  if (!factor) factor = STACK_ALIGN; // stack alignment (16-byte) by default
  return Math.ceil(size / factor) * factor;
}

var Runtime = {
  getNativeTypeSize: getNativeTypeSize,
  alignMemory: alignMemory,

  //! Returns the size of a structure field, as C/C++ would have it (in 32-bit,
  //! for now).
  //! @param type The type, by name.
  getNativeFieldSize: function(type) {
    return Math.max(Runtime.getNativeTypeSize(type), Runtime.QUANTUM_SIZE);
  },

  STACK_ALIGN: {{{ STACK_ALIGN }}},
  POINTER_SIZE: 4,

  // type can be a native type or a struct (or null, for structs we only look at size here)
  getAlignSize: function(type, size, vararg) {
    // we align i64s and doubles on 64-bit boundaries, unlike x86
    if (!vararg && (type == 'i64' || type == 'double')) return 8;
    if (!type) return Math.min(size, 8); // align structures internally to 64 bits
    return Math.min(size || (type ? Runtime.getNativeFieldSize(type) : 0), Runtime.QUANTUM_SIZE);
  }
};

// Additional runtime elements, that need preprocessing

// Converts a value we have as signed, into an unsigned value. For
// example, -1 in int32 would be a very large number as unsigned.
function unSign(value, bits, ignore) {
  if (value >= 0) {
    return value;
  }
  return bits <= 32 ? 2*Math.abs(1 << (bits-1)) + value // Need some trickery, since if bits == 32, we are right at the limit of the bits JS uses in bitshifts
                    : Math.pow(2, bits)         + value;
}

// Converts a value we have as unsigned, into a signed value. For
// example, 200 in a uint8 would be a negative number.
function reSign(value, bits, ignore) {
  if (value <= 0) {
    return value;
  }
  var half = bits <= 32 ? Math.abs(1 << (bits-1)) // abs is needed if bits == 32
                        : Math.pow(2, bits-1);
  if (value >= half && (bits <= 32 || value > half)) { // for huge values, we can hit the precision limit and always get true here. so don't do that
                                                       // but, in general there is no perfect solution here. With 64-bit ints, we get rounding and errors
                                                       // TODO: In i64 mode 1, resign the two parts separately and safely
    value = -2*half + value; // Cannot bitshift half, as it may be at the limit of the bits JS uses in bitshifts
  }
  return value;
}