mirror of
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596 lines
22 KiB
C++
596 lines
22 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla code.
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*
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* The Initial Developer of the Original Code is the Mozilla Corporation.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Benoit Jacob <bjacob@mozilla.com>
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* Jeff Muizelaar <jmuizelaar@mozilla.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#ifndef mozilla_CheckedInt_h
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#define mozilla_CheckedInt_h
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#include "prtypes.h"
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#include <climits>
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namespace mozilla {
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namespace CheckedInt_internal {
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/* we don't want to use std::numeric_limits here because PRInt... types may not support it,
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* depending on the platform, e.g. on certain platforms they use nonstandard built-in types
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*/
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/*** Step 1: manually record information for all the types that we want to support
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***/
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struct unsupported_type {};
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template<typename T> struct integer_type_manually_recorded_info
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{
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enum { is_supported = 0 };
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typedef unsupported_type twice_bigger_type;
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typedef unsupported_type unsigned_type;
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};
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#define CHECKEDINT_REGISTER_SUPPORTED_TYPE(T,_twice_bigger_type,_unsigned_type) \
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template<> struct integer_type_manually_recorded_info<T> \
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{ \
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enum { is_supported = 1 }; \
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typedef _twice_bigger_type twice_bigger_type; \
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typedef _unsigned_type unsigned_type; \
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static void TYPE_NOT_SUPPORTED_BY_CheckedInt() {} \
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};
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// Type Twice Bigger Type Unsigned Type
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRInt8, PRInt16, PRUint8)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRUint8, PRUint16, PRUint8)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRInt16, PRInt32, PRUint16)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRUint16, PRUint32, PRUint16)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRInt32, PRInt64, PRUint32)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRUint32, PRUint64, PRUint32)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRInt64, unsupported_type, PRUint64)
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CHECKEDINT_REGISTER_SUPPORTED_TYPE(PRUint64, unsupported_type, PRUint64)
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/*** Step 2: record some info about a given integer type,
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*** including whether it is supported, whether a twice bigger integer type
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*** is supported, what that twice bigger type is, and some stuff as found
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*** in std::numeric_limits (which we don't use because PRInt.. types may
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*** not support it, if they are defined directly from compiler built-in types).
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*** We use function names min_value() and max_value() instead of min() and max()
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*** because of stupid min/max macros in Windows headers.
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***/
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template<typename T> struct is_unsupported_type { enum { answer = 0 }; };
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template<> struct is_unsupported_type<unsupported_type> { enum { answer = 1 }; };
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template<typename T> struct integer_traits
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{
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typedef typename integer_type_manually_recorded_info<T>::twice_bigger_type twice_bigger_type;
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typedef typename integer_type_manually_recorded_info<T>::unsigned_type unsigned_type;
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enum {
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is_supported = integer_type_manually_recorded_info<T>::is_supported,
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twice_bigger_type_is_supported
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= is_unsupported_type<
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typename integer_type_manually_recorded_info<T>::twice_bigger_type
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>::answer ? 0 : 1,
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size = sizeof(T),
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position_of_sign_bit = CHAR_BIT * size - 1,
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is_signed = (T(-1) > T(0)) ? 0 : 1
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};
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static T min_value()
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{
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// bitwise ops may return a larger type, that's why we cast explicitly to T
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// in C++, left bit shifts on signed values is undefined by the standard unless the shifted value is representable.
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// notice that signed-to-unsigned conversions are always well-defined in the standard,
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// as the value congruent to 2^n as expected. By contrast, unsigned-to-signed is only well-defined if the value is
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// representable.
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return is_signed ? T(unsigned_type(1) << position_of_sign_bit) : T(0);
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}
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static T max_value()
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{
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return ~min_value();
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}
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};
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/*** Step 3: Implement the actual validity checks --- ideas taken from IntegerLib, code different.
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***/
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// bitwise ops may return a larger type, so it's good to use these inline helpers guaranteeing that
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// the result is really of type T
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template<typename T> inline T has_sign_bit(T x)
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{
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// in C++, right bit shifts on negative values is undefined by the standard.
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// notice that signed-to-unsigned conversions are always well-defined in the standard,
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// as the value congruent modulo 2^n as expected. By contrast, unsigned-to-signed is only well-defined if the value is
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// representable. Here the unsigned-to-signed conversion is OK because the value (the result of the shift) is 0 or 1.
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typedef typename integer_traits<T>::unsigned_type unsigned_T;
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return T(unsigned_T(x) >> integer_traits<T>::position_of_sign_bit);
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}
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template<typename T> inline T binary_complement(T x)
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{
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return ~x;
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}
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template<typename T, typename U,
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bool is_T_signed = integer_traits<T>::is_signed,
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bool is_U_signed = integer_traits<U>::is_signed>
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struct is_in_range_impl {};
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template<typename T, typename U>
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struct is_in_range_impl<T, U, true, true>
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{
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static T run(U x)
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{
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return (x <= integer_traits<T>::max_value()) &&
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(x >= integer_traits<T>::min_value());
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}
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};
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template<typename T, typename U>
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struct is_in_range_impl<T, U, false, false>
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{
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static T run(U x)
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{
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return x <= integer_traits<T>::max_value();
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}
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};
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template<typename T, typename U>
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struct is_in_range_impl<T, U, true, false>
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{
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static T run(U x)
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{
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if (sizeof(T) > sizeof(U))
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return 1;
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else
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return x <= U(integer_traits<T>::max_value());
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}
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};
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template<typename T, typename U>
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struct is_in_range_impl<T, U, false, true>
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{
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static T run(U x)
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{
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if (sizeof(T) >= sizeof(U))
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return x >= 0;
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else
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return (x >= 0) && (x <= U(integer_traits<T>::max_value()));
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}
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};
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template<typename T, typename U> inline T is_in_range(U x)
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{
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return is_in_range_impl<T, U>::run(x);
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}
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template<typename T> inline T is_add_valid(T x, T y, T result)
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{
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return integer_traits<T>::is_signed ?
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// addition is valid if the sign of x+y is equal to either that of x or that of y.
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// Beware! These bitwise operations can return a larger integer type, if T was a
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// small type like int8, so we explicitly cast to T.
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has_sign_bit(binary_complement(T((result^x) & (result^y))))
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:
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binary_complement(x) >= y;
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}
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template<typename T> inline T is_sub_valid(T x, T y, T result)
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{
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return integer_traits<T>::is_signed ?
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// substraction is valid if either x and y have same sign, or x-y and x have same sign
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has_sign_bit(binary_complement(T((result^x) & (x^y))))
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:
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x >= y;
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}
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template<typename T,
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bool is_signed = integer_traits<T>::is_signed,
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bool twice_bigger_type_is_supported = integer_traits<T>::twice_bigger_type_is_supported>
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struct is_mul_valid_impl {};
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template<typename T, bool is_signed>
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struct is_mul_valid_impl<T, is_signed, true>
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{
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static T run(T x, T y)
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{
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typedef typename integer_traits<T>::twice_bigger_type twice_bigger_type;
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twice_bigger_type product = twice_bigger_type(x) * twice_bigger_type(y);
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return is_in_range<T>(product);
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}
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};
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template<typename T>
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struct is_mul_valid_impl<T, true, false>
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{
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static T run(T x, T y)
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{
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const T max_value = integer_traits<T>::max_value();
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const T min_value = integer_traits<T>::min_value();
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if (x == 0 || y == 0) return true;
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if (x > 0) {
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if (y > 0)
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return x <= max_value / y;
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else
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return y >= min_value / x;
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} else {
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if (y > 0)
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return x >= min_value / y;
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else
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return y >= max_value / x;
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}
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}
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};
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template<typename T>
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struct is_mul_valid_impl<T, false, false>
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{
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static T run(T x, T y)
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{
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const T max_value = integer_traits<T>::max_value();
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if (x == 0 || y == 0) return true;
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return x <= max_value / y;
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}
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};
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template<typename T> inline T is_mul_valid(T x, T y, T /*result not used*/)
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{
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return is_mul_valid_impl<T>::run(x, y);
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}
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template<typename T> inline T is_div_valid(T x, T y)
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{
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return integer_traits<T>::is_signed ?
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// keep in mind that min/-1 is invalid because abs(min)>max
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(y != 0) && (x != integer_traits<T>::min_value() || y != T(-1))
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:
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y != 0;
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}
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// this is just to shut up msvc warnings about negating unsigned ints.
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template<typename T, bool is_signed = integer_traits<T>::is_signed>
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struct opposite_if_signed_impl
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{
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static T run(T x) { return -x; }
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};
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template<typename T>
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struct opposite_if_signed_impl<T, false>
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{
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static T run(T x) { return x; }
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};
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template<typename T>
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inline T opposite_if_signed(T x) { return opposite_if_signed_impl<T>::run(x); }
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} // end namespace CheckedInt_internal
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/*** Step 4: Now define the CheckedInt class.
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***/
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/** \class CheckedInt
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* \brief Integer wrapper class checking for integer overflow and other errors
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* \param T the integer type to wrap. Can be any of PRInt8, PRUint8, PRInt16, PRUint16,
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* PRInt32, PRUint32, PRInt64, PRUint64.
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*
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* This class implements guarded integer arithmetic. Do a computation, check that
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* valid() returns true, you then have a guarantee that no problem, such as integer overflow,
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* happened during this computation.
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*
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* The arithmetic operators in this class are guaranteed not to crash your app
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* in case of a division by zero.
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*
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* For example, suppose that you want to implement a function that computes (x+y)/z,
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* that doesn't crash if z==0, and that reports on error (divide by zero or integer overflow).
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* You could code it as follows:
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\code
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PRBool compute_x_plus_y_over_z(PRInt32 x, PRInt32 y, PRInt32 z, PRInt32 *result)
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{
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CheckedInt<PRInt32> checked_result = (CheckedInt<PRInt32>(x) + y) / z;
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*result = checked_result.value();
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return checked_result.valid();
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}
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\endcode
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*
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* Implicit conversion from plain integers to checked integers is allowed. The plain integer
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* is checked to be in range before being casted to the destination type. This means that the following
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* lines all compile, and the resulting CheckedInts are correctly detected as valid or invalid:
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* \code
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CheckedInt<PRUint8> x(1); // 1 is of type int, is found to be in range for PRUint8, x is valid
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CheckedInt<PRUint8> x(-1); // -1 is of type int, is found not to be in range for PRUint8, x is invalid
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CheckedInt<PRInt8> x(-1); // -1 is of type int, is found to be in range for PRInt8, x is valid
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CheckedInt<PRInt8> x(PRInt16(1000)); // 1000 is of type PRInt16, is found not to be in range for PRInt8, x is invalid
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CheckedInt<PRInt32> x(PRUint32(3123456789)); // 3123456789 is of type PRUint32, is found not to be in range
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// for PRInt32, x is invalid
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* \endcode
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* Implicit conversion from
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* checked integers to plain integers is not allowed. As shown in the
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* above example, to get the value of a checked integer as a normal integer, call value().
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*
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* Arithmetic operations between checked and plain integers is allowed; the result type
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* is the type of the checked integer.
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*
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* Checked integers of different types cannot be used in the same arithmetic expression.
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*
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* There are convenience typedefs for all PR integer types, of the following form (these are just 2 examples):
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\code
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typedef CheckedInt<PRInt32> CheckedInt32;
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typedef CheckedInt<PRUint16> CheckedUint16;
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\endcode
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*/
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template<typename T>
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class CheckedInt
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{
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protected:
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T mValue;
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T mIsValid; // stored as a T to limit the number of integer conversions when
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// evaluating nested arithmetic expressions.
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template<typename U>
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CheckedInt(U value, T isValid) : mValue(value), mIsValid(isValid)
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{
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CheckedInt_internal::integer_type_manually_recorded_info<T>
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::TYPE_NOT_SUPPORTED_BY_CheckedInt();
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}
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public:
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/** Constructs a checked integer with given \a value. The checked integer is initialized as valid or invalid
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* depending on whether the \a value is in range.
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*
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* This constructor is not explicit. Instead, the type of its argument is a separate template parameter,
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* ensuring that no conversion is performed before this constructor is actually called.
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* As explained in the above documentation for class CheckedInt, this constructor checks that its argument is
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* valid.
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*/
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template<typename U>
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CheckedInt(U value)
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: mValue(T(value)),
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mIsValid(CheckedInt_internal::is_in_range<T>(value))
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{
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CheckedInt_internal::integer_type_manually_recorded_info<T>
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::TYPE_NOT_SUPPORTED_BY_CheckedInt();
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}
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/** Constructs a valid checked integer with initial value 0 */
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CheckedInt() : mValue(0), mIsValid(1)
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{
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CheckedInt_internal::integer_type_manually_recorded_info<T>
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::TYPE_NOT_SUPPORTED_BY_CheckedInt();
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}
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/** \returns the actual value */
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T value() const { return mValue; }
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/** \returns PR_TRUE if the checked integer is valid, i.e. is not the result
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* of an invalid operation or of an operation involving an invalid checked integer
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*/
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PRBool valid() const
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{
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return PRBool(mIsValid);
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}
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/** \returns the sum. Checks for overflow. */
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template<typename U> friend CheckedInt<U> operator +(const CheckedInt<U>& lhs, const CheckedInt<U>& rhs);
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/** Adds. Checks for overflow. \returns self reference */
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template<typename U> CheckedInt& operator +=(U rhs);
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/** \returns the difference. Checks for overflow. */
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template<typename U> friend CheckedInt<U> operator -(const CheckedInt<U>& lhs, const CheckedInt<U> &rhs);
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/** Substracts. Checks for overflow. \returns self reference */
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template<typename U> CheckedInt& operator -=(U rhs);
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/** \returns the product. Checks for overflow. */
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template<typename U> friend CheckedInt<U> operator *(const CheckedInt<U>& lhs, const CheckedInt<U> &rhs);
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/** Multiplies. Checks for overflow. \returns self reference */
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template<typename U> CheckedInt& operator *=(U rhs);
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/** \returns the quotient. Checks for overflow and for divide-by-zero. */
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template<typename U> friend CheckedInt<U> operator /(const CheckedInt<U>& lhs, const CheckedInt<U> &rhs);
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/** Divides. Checks for overflow and for divide-by-zero. \returns self reference */
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template<typename U> CheckedInt& operator /=(U rhs);
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/** \returns the opposite value. Checks for overflow. */
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CheckedInt operator -() const
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{
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// circumvent msvc warning about - applied to unsigned int.
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// if we're unsigned, the only valid case anyway is 0 in which case - is a no-op.
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T result = CheckedInt_internal::opposite_if_signed(value());
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/* give the compiler a good chance to perform RVO */
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return CheckedInt(result,
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mIsValid & CheckedInt_internal::is_sub_valid(T(0), value(), result));
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}
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/** \returns true if the left and right hand sides are valid and have the same value. */
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PRBool operator ==(const CheckedInt& other) const
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{
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return PRBool(mIsValid & other.mIsValid & (value() == other.mValue));
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}
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/** prefix ++ */
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CheckedInt& operator++()
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{
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*this = *this + 1;
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return *this;
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}
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/** postfix ++ */
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CheckedInt operator++(int)
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{
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CheckedInt tmp = *this;
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*this = *this + 1;
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return tmp;
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}
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/** prefix -- */
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CheckedInt& operator--()
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{
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*this = *this - 1;
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return *this;
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}
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/** postfix -- */
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CheckedInt operator--(int)
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{
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CheckedInt tmp = *this;
|
|
*this = *this - 1;
|
|
return tmp;
|
|
}
|
|
|
|
private:
|
|
/** operator!= is disabled. Indeed, (a!=b) should be the same as !(a==b) but that
|
|
* would mean that if a or b is invalid, (a!=b) is always true, which is very tricky.
|
|
*/
|
|
template<typename U>
|
|
PRBool operator !=(U other) const { return !(*this == other); }
|
|
};
|
|
|
|
#define CHECKEDINT_BASIC_BINARY_OPERATOR(NAME, OP) \
|
|
template<typename T> \
|
|
inline CheckedInt<T> operator OP(const CheckedInt<T> &lhs, const CheckedInt<T> &rhs) \
|
|
{ \
|
|
T x = lhs.mValue; \
|
|
T y = rhs.mValue; \
|
|
T result = x OP y; \
|
|
T is_op_valid \
|
|
= CheckedInt_internal::is_##NAME##_valid(x, y, result); \
|
|
/* give the compiler a good chance to perform RVO */ \
|
|
return CheckedInt<T>(result, \
|
|
lhs.mIsValid & rhs.mIsValid & is_op_valid); \
|
|
}
|
|
|
|
CHECKEDINT_BASIC_BINARY_OPERATOR(add, +)
|
|
CHECKEDINT_BASIC_BINARY_OPERATOR(sub, -)
|
|
CHECKEDINT_BASIC_BINARY_OPERATOR(mul, *)
|
|
|
|
// division can't be implemented by CHECKEDINT_BASIC_BINARY_OPERATOR
|
|
// because if rhs == 0, we are not allowed to even try to compute the quotient.
|
|
template<typename T>
|
|
inline CheckedInt<T> operator /(const CheckedInt<T> &lhs, const CheckedInt<T> &rhs)
|
|
{
|
|
T x = lhs.mValue;
|
|
T y = rhs.mValue;
|
|
T is_op_valid = CheckedInt_internal::is_div_valid(x, y);
|
|
T result = is_op_valid ? (x / y) : 0;
|
|
/* give the compiler a good chance to perform RVO */
|
|
return CheckedInt<T>(result,
|
|
lhs.mIsValid & rhs.mIsValid & is_op_valid);
|
|
}
|
|
|
|
// implement cast_to_CheckedInt<T>(x), making sure that
|
|
// - it allows x to be either a CheckedInt<T> or any integer type that can be casted to T
|
|
// - if x is already a CheckedInt<T>, we just return a reference to it, instead of copying it (optimization)
|
|
|
|
template<typename T, typename U>
|
|
struct cast_to_CheckedInt_impl
|
|
{
|
|
typedef CheckedInt<T> return_type;
|
|
static CheckedInt<T> run(U u) { return u; }
|
|
};
|
|
|
|
template<typename T>
|
|
struct cast_to_CheckedInt_impl<T, CheckedInt<T> >
|
|
{
|
|
typedef const CheckedInt<T>& return_type;
|
|
static const CheckedInt<T>& run(const CheckedInt<T>& u) { return u; }
|
|
};
|
|
|
|
template<typename T, typename U>
|
|
inline typename cast_to_CheckedInt_impl<T, U>::return_type
|
|
cast_to_CheckedInt(U u)
|
|
{
|
|
return cast_to_CheckedInt_impl<T, U>::run(u);
|
|
}
|
|
|
|
#define CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(OP, COMPOUND_OP) \
|
|
template<typename T> \
|
|
template<typename U> \
|
|
CheckedInt<T>& CheckedInt<T>::operator COMPOUND_OP(U rhs) \
|
|
{ \
|
|
*this = *this OP cast_to_CheckedInt<T>(rhs); \
|
|
return *this; \
|
|
} \
|
|
template<typename T, typename U> \
|
|
inline CheckedInt<T> operator OP(const CheckedInt<T> &lhs, U rhs) \
|
|
{ \
|
|
return lhs OP cast_to_CheckedInt<T>(rhs); \
|
|
} \
|
|
template<typename T, typename U> \
|
|
inline CheckedInt<T> operator OP(U lhs, const CheckedInt<T> &rhs) \
|
|
{ \
|
|
return cast_to_CheckedInt<T>(lhs) OP rhs; \
|
|
}
|
|
|
|
CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(+, +=)
|
|
CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(*, *=)
|
|
CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(-, -=)
|
|
CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(/, /=)
|
|
|
|
template<typename T, typename U>
|
|
inline PRBool operator ==(const CheckedInt<T> &lhs, U rhs)
|
|
{
|
|
return lhs == cast_to_CheckedInt<T>(rhs);
|
|
}
|
|
|
|
template<typename T, typename U>
|
|
inline PRBool operator ==(U lhs, const CheckedInt<T> &rhs)
|
|
{
|
|
return cast_to_CheckedInt<T>(lhs) == rhs;
|
|
}
|
|
|
|
// convenience typedefs.
|
|
// the use of a macro here helps make sure that we don't let a typo slip into some of these.
|
|
#define CHECKEDINT_MAKE_TYPEDEF(Type) \
|
|
typedef CheckedInt<PR##Type> Checked##Type;
|
|
|
|
CHECKEDINT_MAKE_TYPEDEF(Int8)
|
|
CHECKEDINT_MAKE_TYPEDEF(Uint8)
|
|
CHECKEDINT_MAKE_TYPEDEF(Int16)
|
|
CHECKEDINT_MAKE_TYPEDEF(Uint16)
|
|
CHECKEDINT_MAKE_TYPEDEF(Int32)
|
|
CHECKEDINT_MAKE_TYPEDEF(Uint32)
|
|
CHECKEDINT_MAKE_TYPEDEF(Int64)
|
|
CHECKEDINT_MAKE_TYPEDEF(Uint64)
|
|
|
|
} // end namespace mozilla
|
|
|
|
#endif /* mozilla_CheckedInt_h */
|