189 lines
7.2 KiB
C
189 lines
7.2 KiB
C
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/*
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* Copyright 2014 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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// Borrowed from Chromium's src/base/numerics/safe_conversions_impl.h.
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#ifndef WEBRTC_BASE_SAFE_CONVERSIONS_IMPL_H_
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#define WEBRTC_BASE_SAFE_CONVERSIONS_IMPL_H_
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#include <limits>
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namespace rtc {
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namespace internal {
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enum DstSign {
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DST_UNSIGNED,
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DST_SIGNED
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};
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enum SrcSign {
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SRC_UNSIGNED,
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SRC_SIGNED
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};
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enum DstRange {
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OVERLAPS_RANGE,
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CONTAINS_RANGE
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};
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// Helper templates to statically determine if our destination type can contain
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// all values represented by the source type.
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template <typename Dst, typename Src,
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DstSign IsDstSigned = std::numeric_limits<Dst>::is_signed ?
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DST_SIGNED : DST_UNSIGNED,
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SrcSign IsSrcSigned = std::numeric_limits<Src>::is_signed ?
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SRC_SIGNED : SRC_UNSIGNED>
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struct StaticRangeCheck {};
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template <typename Dst, typename Src>
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struct StaticRangeCheck<Dst, Src, DST_SIGNED, SRC_SIGNED> {
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typedef std::numeric_limits<Dst> DstLimits;
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typedef std::numeric_limits<Src> SrcLimits;
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// Compare based on max_exponent, which we must compute for integrals.
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static const size_t kDstMaxExponent = DstLimits::is_iec559 ?
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DstLimits::max_exponent :
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(sizeof(Dst) * 8 - 1);
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static const size_t kSrcMaxExponent = SrcLimits::is_iec559 ?
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SrcLimits::max_exponent :
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(sizeof(Src) * 8 - 1);
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static const DstRange value = kDstMaxExponent >= kSrcMaxExponent ?
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CONTAINS_RANGE : OVERLAPS_RANGE;
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};
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template <typename Dst, typename Src>
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struct StaticRangeCheck<Dst, Src, DST_UNSIGNED, SRC_UNSIGNED> {
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static const DstRange value = sizeof(Dst) >= sizeof(Src) ?
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CONTAINS_RANGE : OVERLAPS_RANGE;
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};
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template <typename Dst, typename Src>
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struct StaticRangeCheck<Dst, Src, DST_SIGNED, SRC_UNSIGNED> {
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typedef std::numeric_limits<Dst> DstLimits;
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typedef std::numeric_limits<Src> SrcLimits;
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// Compare based on max_exponent, which we must compute for integrals.
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static const size_t kDstMaxExponent = DstLimits::is_iec559 ?
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DstLimits::max_exponent :
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(sizeof(Dst) * 8 - 1);
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static const size_t kSrcMaxExponent = sizeof(Src) * 8;
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static const DstRange value = kDstMaxExponent >= kSrcMaxExponent ?
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CONTAINS_RANGE : OVERLAPS_RANGE;
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};
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template <typename Dst, typename Src>
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struct StaticRangeCheck<Dst, Src, DST_UNSIGNED, SRC_SIGNED> {
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static const DstRange value = OVERLAPS_RANGE;
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};
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enum RangeCheckResult {
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TYPE_VALID = 0, // Value can be represented by the destination type.
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TYPE_UNDERFLOW = 1, // Value would overflow.
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TYPE_OVERFLOW = 2, // Value would underflow.
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TYPE_INVALID = 3 // Source value is invalid (i.e. NaN).
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};
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// This macro creates a RangeCheckResult from an upper and lower bound
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// check by taking advantage of the fact that only NaN can be out of range in
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// both directions at once.
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#define BASE_NUMERIC_RANGE_CHECK_RESULT(is_in_upper_bound, is_in_lower_bound) \
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RangeCheckResult(((is_in_upper_bound) ? 0 : TYPE_OVERFLOW) | \
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((is_in_lower_bound) ? 0 : TYPE_UNDERFLOW))
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template <typename Dst,
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typename Src,
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DstSign IsDstSigned = std::numeric_limits<Dst>::is_signed ?
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DST_SIGNED : DST_UNSIGNED,
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SrcSign IsSrcSigned = std::numeric_limits<Src>::is_signed ?
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SRC_SIGNED : SRC_UNSIGNED,
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DstRange IsSrcRangeContained = StaticRangeCheck<Dst, Src>::value>
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struct RangeCheckImpl {};
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// The following templates are for ranges that must be verified at runtime. We
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// split it into checks based on signedness to avoid confusing casts and
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// compiler warnings on signed an unsigned comparisons.
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// Dst range always contains the result: nothing to check.
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template <typename Dst, typename Src, DstSign IsDstSigned, SrcSign IsSrcSigned>
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struct RangeCheckImpl<Dst, Src, IsDstSigned, IsSrcSigned, CONTAINS_RANGE> {
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static RangeCheckResult Check(Src value) {
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return TYPE_VALID;
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}
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};
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// Signed to signed narrowing.
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template <typename Dst, typename Src>
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struct RangeCheckImpl<Dst, Src, DST_SIGNED, SRC_SIGNED, OVERLAPS_RANGE> {
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static RangeCheckResult Check(Src value) {
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typedef std::numeric_limits<Dst> DstLimits;
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return DstLimits::is_iec559 ?
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BASE_NUMERIC_RANGE_CHECK_RESULT(
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value <= static_cast<Src>(DstLimits::max()),
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value >= static_cast<Src>(DstLimits::max() * -1)) :
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BASE_NUMERIC_RANGE_CHECK_RESULT(
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value <= static_cast<Src>(DstLimits::max()),
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value >= static_cast<Src>(DstLimits::min()));
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}
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};
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// Unsigned to unsigned narrowing.
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template <typename Dst, typename Src>
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struct RangeCheckImpl<Dst, Src, DST_UNSIGNED, SRC_UNSIGNED, OVERLAPS_RANGE> {
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static RangeCheckResult Check(Src value) {
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typedef std::numeric_limits<Dst> DstLimits;
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return BASE_NUMERIC_RANGE_CHECK_RESULT(
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value <= static_cast<Src>(DstLimits::max()), true);
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}
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};
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// Unsigned to signed.
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template <typename Dst, typename Src>
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struct RangeCheckImpl<Dst, Src, DST_SIGNED, SRC_UNSIGNED, OVERLAPS_RANGE> {
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static RangeCheckResult Check(Src value) {
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typedef std::numeric_limits<Dst> DstLimits;
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return sizeof(Dst) > sizeof(Src) ? TYPE_VALID :
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BASE_NUMERIC_RANGE_CHECK_RESULT(
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value <= static_cast<Src>(DstLimits::max()), true);
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}
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};
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// Signed to unsigned.
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template <typename Dst, typename Src>
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struct RangeCheckImpl<Dst, Src, DST_UNSIGNED, SRC_SIGNED, OVERLAPS_RANGE> {
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static RangeCheckResult Check(Src value) {
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typedef std::numeric_limits<Dst> DstLimits;
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typedef std::numeric_limits<Src> SrcLimits;
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// Compare based on max_exponent, which we must compute for integrals.
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static const size_t kDstMaxExponent = sizeof(Dst) * 8;
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static const size_t kSrcMaxExponent = SrcLimits::is_iec559 ?
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SrcLimits::max_exponent :
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(sizeof(Src) * 8 - 1);
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return (kDstMaxExponent >= kSrcMaxExponent) ?
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BASE_NUMERIC_RANGE_CHECK_RESULT(true, value >= static_cast<Src>(0)) :
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BASE_NUMERIC_RANGE_CHECK_RESULT(
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value <= static_cast<Src>(DstLimits::max()),
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value >= static_cast<Src>(0));
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}
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};
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template <typename Dst, typename Src>
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inline RangeCheckResult RangeCheck(Src value) {
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static_assert(std::numeric_limits<Src>::is_specialized,
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"argument must be numeric");
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static_assert(std::numeric_limits<Dst>::is_specialized,
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"result must be numeric");
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return RangeCheckImpl<Dst, Src>::Check(value);
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}
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} // namespace internal
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} // namespace rtc
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#endif // WEBRTC_BASE_SAFE_CONVERSIONS_IMPL_H_
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