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double-conversion / src / utils.h

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// Copyright 2006-2008 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
//       copyright notice, this list of conditions and the following
//       disclaimer in the documentation and/or other materials provided
//       with the distribution.
//     * Neither the name of Google Inc. nor the names of its
//       contributors may be used to endorse or promote products derived
//       from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef V8_UTILS_H_
#define V8_UTILS_H_

#include <stdlib.h>
#include <string.h>

namespace v8 {
namespace internal {

// Returns the maximum of the two parameters.
template <typename T>
static T Max(T a, T b) {
  return a < b ? b : a;
}


// Returns the minimum of the two parameters.
template <typename T>
static T Min(T a, T b) {
  return a < b ? a : b;
}


inline int StrLength(const char* string) {
  size_t length = strlen(string);
  ASSERT(length == static_cast<size_t>(static_cast<int>(length)));
  return static_cast<int>(length);
}


template <typename T>
class Vector {
 public:
  Vector() : start_(NULL), length_(0) {}
  Vector(T* data, int length) : start_(data), length_(length) {
    ASSERT(length == 0 || (length > 0 && data != NULL));
  }

  // Returns a vector using the same backing storage as this one,
  // spanning from and including 'from', to but not including 'to'.
  Vector<T> SubVector(int from, int to) {
    ASSERT(to <= length_);
    ASSERT(from < to);
    ASSERT(0 <= from);
    return Vector<T>(start() + from, to - from);
  }

  // Returns the length of the vector.
  int length() const { return length_; }

  // Returns whether or not the vector is empty.
  bool is_empty() const { return length_ == 0; }

  // Returns the pointer to the start of the data in the vector.
  T* start() const { return start_; }

  // Access individual vector elements - checks bounds in debug mode.
  T& operator[](int index) const {
    ASSERT(0 <= index && index < length_);
    return start_[index];
  }

  T& first() { return start_[0]; }

  T& last() { return start_[length_ - 1]; }

 private:
  T* start_;
  int length_;
};


// The type-based aliasing rule allows the compiler to assume that pointers of
// different types (for some definition of different) never alias each other.
// Thus the following code does not work:
//
// float f = foo();
// int fbits = *(int*)(&f);
//
// The compiler 'knows' that the int pointer can't refer to f since the types
// don't match, so the compiler may cache f in a register, leaving random data
// in fbits.  Using C++ style casts makes no difference, however a pointer to
// char data is assumed to alias any other pointer.  This is the 'memcpy
// exception'.
//
// Bit_cast uses the memcpy exception to move the bits from a variable of one
// type of a variable of another type.  Of course the end result is likely to
// be implementation dependent.  Most compilers (gcc-4.2 and MSVC 2005)
// will completely optimize BitCast away.
//
// There is an additional use for BitCast.
// Recent gccs will warn when they see casts that may result in breakage due to
// the type-based aliasing rule.  If you have checked that there is no breakage
// you can use BitCast to cast one pointer type to another.  This confuses gcc
// enough that it can no longer see that you have cast one pointer type to
// another thus avoiding the warning.
template <class Dest, class Source>
inline Dest BitCast(const Source& source) {
  // Compile time assertion: sizeof(Dest) == sizeof(Source)
  // A compile error here means your Dest and Source have different sizes.
  typedef char VerifySizesAreEqual[sizeof(Dest) == sizeof(Source) ? 1 : -1];

  Dest dest;
  memcpy(&dest, &source, sizeof(dest));
  return dest;
}

template <class Dest, class Source>
inline Dest BitCast(Source* source) {
  return BitCast<Dest>(reinterpret_cast<uintptr_t>(source));
}

} }  // namespace v8::internal

#endif  // V8_UTILS_H_