summaryrefslogtreecommitdiff
path: root/third_party/numerics/safe_conversions_impl.h
diff options
context:
space:
mode:
authorChris Palmer <palmer@google.com>2014-06-20 16:30:49 -0700
committerChris Palmer <palmer@google.com>2014-06-20 16:30:49 -0700
commitd9713f05fdcecab8428d39034c6b84cd0bbd2920 (patch)
tree1bf7cf8f0aff9f917f4e7e0bec1dc51e974c9832 /third_party/numerics/safe_conversions_impl.h
parent63412bf0ec2f6bab77e60dddfb5fc65d0dd95a74 (diff)
downloadpdfium-d9713f05fdcecab8428d39034c6b84cd0bbd2920.tar.xz
Import Chromium base/numerics to resolve integer overflow.
We'll use this for integer overflows going forward. BUG=382606 R=bo_xu@foxitsoftware.com, jschuh@chromium.org Review URL: https://codereview.chromium.org/341533007
Diffstat (limited to 'third_party/numerics/safe_conversions_impl.h')
-rw-r--r--third_party/numerics/safe_conversions_impl.h217
1 files changed, 217 insertions, 0 deletions
diff --git a/third_party/numerics/safe_conversions_impl.h b/third_party/numerics/safe_conversions_impl.h
new file mode 100644
index 0000000000..a357e518d1
--- /dev/null
+++ b/third_party/numerics/safe_conversions_impl.h
@@ -0,0 +1,217 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_SAFE_CONVERSIONS_IMPL_H_
+#define BASE_SAFE_CONVERSIONS_IMPL_H_
+
+#include <limits>
+
+#include "../macros.h"
+#include "../template_util.h"
+
+namespace base {
+namespace internal {
+
+// The std library doesn't provide a binary max_exponent for integers, however
+// we can compute one by adding one to the number of non-sign bits. This allows
+// for accurate range comparisons between floating point and integer types.
+template <typename NumericType>
+struct MaxExponent {
+ static const int value = std::numeric_limits<NumericType>::is_iec559
+ ? std::numeric_limits<NumericType>::max_exponent
+ : (sizeof(NumericType) * 8 + 1 -
+ std::numeric_limits<NumericType>::is_signed);
+};
+
+enum IntegerRepresentation {
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED
+};
+
+// A range for a given nunmeric Src type is contained for a given numeric Dst
+// type if both numeric_limits<Src>::max() <= numeric_limits<Dst>::max() and
+// numeric_limits<Src>::min() >= numeric_limits<Dst>::min() are true.
+// We implement this as template specializations rather than simple static
+// comparisons to ensure type correctness in our comparisons.
+enum NumericRangeRepresentation {
+ NUMERIC_RANGE_NOT_CONTAINED,
+ NUMERIC_RANGE_CONTAINED
+};
+
+// Helper templates to statically determine if our destination type can contain
+// maximum and minimum values represented by the source type.
+
+template <
+ typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ IntegerRepresentation SrcSign =
+ std::numeric_limits<Src>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED >
+struct StaticDstRangeRelationToSrcRange;
+
+// Same sign: Dst is guaranteed to contain Src only if its range is equal or
+// larger.
+template <typename Dst, typename Src, IntegerRepresentation Sign>
+struct StaticDstRangeRelationToSrcRange<Dst, Src, Sign, Sign> {
+ static const NumericRangeRepresentation value =
+ MaxExponent<Dst>::value >= MaxExponent<Src>::value
+ ? NUMERIC_RANGE_CONTAINED
+ : NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+// Unsigned to signed: Dst is guaranteed to contain source only if its range is
+// larger.
+template <typename Dst, typename Src>
+struct StaticDstRangeRelationToSrcRange<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED> {
+ static const NumericRangeRepresentation value =
+ MaxExponent<Dst>::value > MaxExponent<Src>::value
+ ? NUMERIC_RANGE_CONTAINED
+ : NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+// Signed to unsigned: Dst cannot be statically determined to contain Src.
+template <typename Dst, typename Src>
+struct StaticDstRangeRelationToSrcRange<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED> {
+ static const NumericRangeRepresentation value = NUMERIC_RANGE_NOT_CONTAINED;
+};
+
+enum RangeConstraint {
+ RANGE_VALID = 0x0, // Value can be represented by the destination type.
+ RANGE_UNDERFLOW = 0x1, // Value would overflow.
+ RANGE_OVERFLOW = 0x2, // Value would underflow.
+ RANGE_INVALID = RANGE_UNDERFLOW | RANGE_OVERFLOW // Invalid (i.e. NaN).
+};
+
+// Helper function for coercing an int back to a RangeContraint.
+inline RangeConstraint GetRangeConstraint(int integer_range_constraint) {
+ assert(integer_range_constraint >= RANGE_VALID &&
+ integer_range_constraint <= RANGE_INVALID);
+ return static_cast<RangeConstraint>(integer_range_constraint);
+}
+
+// This function creates a RangeConstraint from an upper and lower bound
+// check by taking advantage of the fact that only NaN can be out of range in
+// both directions at once.
+inline RangeConstraint GetRangeConstraint(bool is_in_upper_bound,
+ bool is_in_lower_bound) {
+ return GetRangeConstraint((is_in_upper_bound ? 0 : RANGE_OVERFLOW) |
+ (is_in_lower_bound ? 0 : RANGE_UNDERFLOW));
+}
+
+template <
+ typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ IntegerRepresentation SrcSign = std::numeric_limits<Src>::is_signed
+ ? INTEGER_REPRESENTATION_SIGNED
+ : INTEGER_REPRESENTATION_UNSIGNED,
+ NumericRangeRepresentation DstRange =
+ StaticDstRangeRelationToSrcRange<Dst, Src>::value >
+struct DstRangeRelationToSrcRangeImpl;
+
+// The following templates are for ranges that must be verified at runtime. We
+// split it into checks based on signedness to avoid confusing casts and
+// compiler warnings on signed an unsigned comparisons.
+
+// Dst range is statically determined to contain Src: Nothing to check.
+template <typename Dst,
+ typename Src,
+ IntegerRepresentation DstSign,
+ IntegerRepresentation SrcSign>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ DstSign,
+ SrcSign,
+ NUMERIC_RANGE_CONTAINED> {
+ static RangeConstraint Check(Src value) { return RANGE_VALID; }
+};
+
+// Signed to signed narrowing: Both the upper and lower boundaries may be
+// exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_SIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return std::numeric_limits<Dst>::is_iec559
+ ? GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
+ value >= -std::numeric_limits<Dst>::max())
+ : GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
+ value >= std::numeric_limits<Dst>::min());
+ }
+};
+
+// Unsigned to unsigned narrowing: Only the upper boundary can be exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), true);
+ }
+};
+
+// Unsigned to signed: The upper boundary may be exceeded.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_SIGNED,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return sizeof(Dst) > sizeof(Src)
+ ? RANGE_VALID
+ : GetRangeConstraint(
+ value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
+ true);
+ }
+};
+
+// Signed to unsigned: The upper boundary may be exceeded for a narrower Dst,
+// and any negative value exceeds the lower boundary.
+template <typename Dst, typename Src>
+struct DstRangeRelationToSrcRangeImpl<Dst,
+ Src,
+ INTEGER_REPRESENTATION_UNSIGNED,
+ INTEGER_REPRESENTATION_SIGNED,
+ NUMERIC_RANGE_NOT_CONTAINED> {
+ static RangeConstraint Check(Src value) {
+ return (MaxExponent<Dst>::value >= MaxExponent<Src>::value)
+ ? GetRangeConstraint(true, value >= static_cast<Src>(0))
+ : GetRangeConstraint(
+ value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
+ value >= static_cast<Src>(0));
+ }
+};
+
+template <typename Dst, typename Src>
+inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
+ COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
+ argument_must_be_numeric);
+ COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
+ result_must_be_numeric);
+ return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
+}
+
+} // namespace internal
+} // namespace base
+
+#endif // BASE_SAFE_CONVERSIONS_IMPL_H_
+