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Issue 900753002: Add namespace and re-arrange PDFium's local copy of chromium /base. (Closed) Base URL: https://pdfium.googlesource.com/pdfium.git@master
Patch Set: rename safemath target to pdfium_base Created 5 years, 10 months ago
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1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #ifndef BASE_SAFE_CONVERSIONS_IMPL_H_
6 #define BASE_SAFE_CONVERSIONS_IMPL_H_
7
8 #include <limits>
9
10 #include "../macros.h"
11 #include "../template_util.h"
12
13 namespace base {
14 namespace internal {
15
16 // The std library doesn't provide a binary max_exponent for integers, however
17 // we can compute one by adding one to the number of non-sign bits. This allows
18 // for accurate range comparisons between floating point and integer types.
19 template <typename NumericType>
20 struct MaxExponent {
21 static const int value = std::numeric_limits<NumericType>::is_iec559
22 ? std::numeric_limits<NumericType>::max_exponent
23 : (sizeof(NumericType) * 8 + 1 -
24 std::numeric_limits<NumericType>::is_signed);
25 };
26
27 enum IntegerRepresentation {
28 INTEGER_REPRESENTATION_UNSIGNED,
29 INTEGER_REPRESENTATION_SIGNED
30 };
31
32 // A range for a given nunmeric Src type is contained for a given numeric Dst
33 // type if both numeric_limits<Src>::max() <= numeric_limits<Dst>::max() and
34 // numeric_limits<Src>::min() >= numeric_limits<Dst>::min() are true.
35 // We implement this as template specializations rather than simple static
36 // comparisons to ensure type correctness in our comparisons.
37 enum NumericRangeRepresentation {
38 NUMERIC_RANGE_NOT_CONTAINED,
39 NUMERIC_RANGE_CONTAINED
40 };
41
42 // Helper templates to statically determine if our destination type can contain
43 // maximum and minimum values represented by the source type.
44
45 template <
46 typename Dst,
47 typename Src,
48 IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
49 ? INTEGER_REPRESENTATION_SIGNED
50 : INTEGER_REPRESENTATION_UNSIGNED,
51 IntegerRepresentation SrcSign =
52 std::numeric_limits<Src>::is_signed
53 ? INTEGER_REPRESENTATION_SIGNED
54 : INTEGER_REPRESENTATION_UNSIGNED >
55 struct StaticDstRangeRelationToSrcRange;
56
57 // Same sign: Dst is guaranteed to contain Src only if its range is equal or
58 // larger.
59 template <typename Dst, typename Src, IntegerRepresentation Sign>
60 struct StaticDstRangeRelationToSrcRange<Dst, Src, Sign, Sign> {
61 static const NumericRangeRepresentation value =
62 MaxExponent<Dst>::value >= MaxExponent<Src>::value
63 ? NUMERIC_RANGE_CONTAINED
64 : NUMERIC_RANGE_NOT_CONTAINED;
65 };
66
67 // Unsigned to signed: Dst is guaranteed to contain source only if its range is
68 // larger.
69 template <typename Dst, typename Src>
70 struct StaticDstRangeRelationToSrcRange<Dst,
71 Src,
72 INTEGER_REPRESENTATION_SIGNED,
73 INTEGER_REPRESENTATION_UNSIGNED> {
74 static const NumericRangeRepresentation value =
75 MaxExponent<Dst>::value > MaxExponent<Src>::value
76 ? NUMERIC_RANGE_CONTAINED
77 : NUMERIC_RANGE_NOT_CONTAINED;
78 };
79
80 // Signed to unsigned: Dst cannot be statically determined to contain Src.
81 template <typename Dst, typename Src>
82 struct StaticDstRangeRelationToSrcRange<Dst,
83 Src,
84 INTEGER_REPRESENTATION_UNSIGNED,
85 INTEGER_REPRESENTATION_SIGNED> {
86 static const NumericRangeRepresentation value = NUMERIC_RANGE_NOT_CONTAINED;
87 };
88
89 enum RangeConstraint {
90 RANGE_VALID = 0x0, // Value can be represented by the destination type.
91 RANGE_UNDERFLOW = 0x1, // Value would overflow.
92 RANGE_OVERFLOW = 0x2, // Value would underflow.
93 RANGE_INVALID = RANGE_UNDERFLOW | RANGE_OVERFLOW // Invalid (i.e. NaN).
94 };
95
96 // Helper function for coercing an int back to a RangeContraint.
97 inline RangeConstraint GetRangeConstraint(int integer_range_constraint) {
98 assert(integer_range_constraint >= RANGE_VALID &&
99 integer_range_constraint <= RANGE_INVALID);
100 return static_cast<RangeConstraint>(integer_range_constraint);
101 }
102
103 // This function creates a RangeConstraint from an upper and lower bound
104 // check by taking advantage of the fact that only NaN can be out of range in
105 // both directions at once.
106 inline RangeConstraint GetRangeConstraint(bool is_in_upper_bound,
107 bool is_in_lower_bound) {
108 return GetRangeConstraint((is_in_upper_bound ? 0 : RANGE_OVERFLOW) |
109 (is_in_lower_bound ? 0 : RANGE_UNDERFLOW));
110 }
111
112 template <
113 typename Dst,
114 typename Src,
115 IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed
116 ? INTEGER_REPRESENTATION_SIGNED
117 : INTEGER_REPRESENTATION_UNSIGNED,
118 IntegerRepresentation SrcSign = std::numeric_limits<Src>::is_signed
119 ? INTEGER_REPRESENTATION_SIGNED
120 : INTEGER_REPRESENTATION_UNSIGNED,
121 NumericRangeRepresentation DstRange =
122 StaticDstRangeRelationToSrcRange<Dst, Src>::value >
123 struct DstRangeRelationToSrcRangeImpl;
124
125 // The following templates are for ranges that must be verified at runtime. We
126 // split it into checks based on signedness to avoid confusing casts and
127 // compiler warnings on signed an unsigned comparisons.
128
129 // Dst range is statically determined to contain Src: Nothing to check.
130 template <typename Dst,
131 typename Src,
132 IntegerRepresentation DstSign,
133 IntegerRepresentation SrcSign>
134 struct DstRangeRelationToSrcRangeImpl<Dst,
135 Src,
136 DstSign,
137 SrcSign,
138 NUMERIC_RANGE_CONTAINED> {
139 static RangeConstraint Check(Src value) { return RANGE_VALID; }
140 };
141
142 // Signed to signed narrowing: Both the upper and lower boundaries may be
143 // exceeded.
144 template <typename Dst, typename Src>
145 struct DstRangeRelationToSrcRangeImpl<Dst,
146 Src,
147 INTEGER_REPRESENTATION_SIGNED,
148 INTEGER_REPRESENTATION_SIGNED,
149 NUMERIC_RANGE_NOT_CONTAINED> {
150 static RangeConstraint Check(Src value) {
151 return std::numeric_limits<Dst>::is_iec559
152 ? GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
153 value >= -std::numeric_limits<Dst>::max())
154 : GetRangeConstraint(value <= std::numeric_limits<Dst>::max(),
155 value >= std::numeric_limits<Dst>::min());
156 }
157 };
158
159 // Unsigned to unsigned narrowing: Only the upper boundary can be exceeded.
160 template <typename Dst, typename Src>
161 struct DstRangeRelationToSrcRangeImpl<Dst,
162 Src,
163 INTEGER_REPRESENTATION_UNSIGNED,
164 INTEGER_REPRESENTATION_UNSIGNED,
165 NUMERIC_RANGE_NOT_CONTAINED> {
166 static RangeConstraint Check(Src value) {
167 return GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), true);
168 }
169 };
170
171 // Unsigned to signed: The upper boundary may be exceeded.
172 template <typename Dst, typename Src>
173 struct DstRangeRelationToSrcRangeImpl<Dst,
174 Src,
175 INTEGER_REPRESENTATION_SIGNED,
176 INTEGER_REPRESENTATION_UNSIGNED,
177 NUMERIC_RANGE_NOT_CONTAINED> {
178 static RangeConstraint Check(Src value) {
179 return sizeof(Dst) > sizeof(Src)
180 ? RANGE_VALID
181 : GetRangeConstraint(
182 value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
183 true);
184 }
185 };
186
187 // Signed to unsigned: The upper boundary may be exceeded for a narrower Dst,
188 // and any negative value exceeds the lower boundary.
189 template <typename Dst, typename Src>
190 struct DstRangeRelationToSrcRangeImpl<Dst,
191 Src,
192 INTEGER_REPRESENTATION_UNSIGNED,
193 INTEGER_REPRESENTATION_SIGNED,
194 NUMERIC_RANGE_NOT_CONTAINED> {
195 static RangeConstraint Check(Src value) {
196 return (MaxExponent<Dst>::value >= MaxExponent<Src>::value)
197 ? GetRangeConstraint(true, value >= static_cast<Src>(0))
198 : GetRangeConstraint(
199 value <= static_cast<Src>(std::numeric_limits<Dst>::max()),
200 value >= static_cast<Src>(0));
201 }
202 };
203
204 template <typename Dst, typename Src>
205 inline RangeConstraint DstRangeRelationToSrcRange(Src value) {
206 COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
207 argument_must_be_numeric);
208 COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized,
209 result_must_be_numeric);
210 return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value);
211 }
212
213 } // namespace internal
214 } // namespace base
215
216 #endif // BASE_SAFE_CONVERSIONS_IMPL_H_
217
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