1 /*
2 * Copyright 2013 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef SkTFitsIn_DEFINED
9 #define SkTFitsIn_DEFINED
10
11 #include "SkTypes.h"
12 #include "SkTLogic.h"
13 #include <limits>
14 #include <type_traits>
15
16 namespace sktfitsin {
17 namespace Private {
18
19 /** SkTMux::type = (a && b) ? Both : (a) ? A : (b) ? B : Neither; */
20 template <bool a, bool b, typename Both, typename A, typename B, typename Neither>
21 struct SkTMux {
22 using type = skstd::conditional_t<a, skstd::conditional_t<b, Both, A>,
23 skstd::conditional_t<b, B, Neither>>;
24 };
25
26 /** SkTHasMoreDigits = (digits(A) >= digits(B)) ? true_type : false_type. */
27 template<typename A, typename B> struct SkTHasMoreDigits
28 : skstd::bool_constant<std::numeric_limits<A>::digits >= std::numeric_limits<B>::digits>
29 { };
30
31 /** A high or low side predicate which is used when it is statically known
32 * that source values are in the range of the Destination.
33 */
34 template <typename S> struct SkTOutOfRange_False {
35 typedef std::false_type can_be_true;
36 typedef S source_type;
applySkTOutOfRange_False37 static bool apply(S s) {
38 return false;
39 }
40 };
41
42 /** A low side predicate which tests if the source value < Min(D).
43 * Assumes that Min(S) <= Min(D).
44 */
45 template <typename D, typename S> struct SkTOutOfRange_LT_MinD {
46 typedef std::true_type can_be_true;
47 typedef S source_type;
applySkTOutOfRange_LT_MinD48 static bool apply(S s) {
49 typedef SkTHasMoreDigits<S, D> precondition;
50 static_assert(precondition::value, "SkTOutOfRange_LT_MinD__minS_gt_minD");
51
52 return s < static_cast<S>((std::numeric_limits<D>::min)());
53 }
54 };
55
56 /** A low side predicate which tests if the source value is less than 0. */
57 template <typename D, typename S> struct SkTOutOfRange_LT_Zero {
58 typedef std::true_type can_be_true;
59 typedef S source_type;
applySkTOutOfRange_LT_Zero60 static bool apply(S s) {
61 return s < static_cast<S>(0);
62 }
63 };
64
65 /** A high side predicate which tests if the source value > Max(D).
66 * Assumes that Max(S) >= Max(D).
67 */
68 template <typename D, typename S> struct SkTOutOfRange_GT_MaxD {
69 typedef std::true_type can_be_true;
70 typedef S source_type;
applySkTOutOfRange_GT_MaxD71 static bool apply(S s) {
72 typedef SkTHasMoreDigits<S, D> precondition;
73 static_assert(precondition::value, "SkTOutOfRange_GT_MaxD__maxS_lt_maxD");
74
75 return s > static_cast<S>((std::numeric_limits<D>::max)());
76 }
77 };
78
79 /** Composes two SkTOutOfRange predicates.
80 * First checks OutOfRange_Low then, if in range, OutOfRange_High.
81 */
82 template<class OutOfRange_Low, class OutOfRange_High> struct SkTOutOfRange_Either {
83 typedef std::true_type can_be_true;
84 typedef typename OutOfRange_Low::source_type source_type;
applySkTOutOfRange_Either85 static bool apply(source_type s) {
86 bool outOfRange = OutOfRange_Low::apply(s);
87 if (!outOfRange) {
88 outOfRange = OutOfRange_High::apply(s);
89 }
90 return outOfRange;
91 }
92 };
93
94 /** SkTCombineOutOfRange::type is an SkTOutOfRange_XXX type which is the
95 * optimal combination of OutOfRange_Low and OutOfRange_High.
96 */
97 template<class OutOfRange_Low, class OutOfRange_High> struct SkTCombineOutOfRange {
98 typedef SkTOutOfRange_Either<OutOfRange_Low, OutOfRange_High> Both;
99 typedef SkTOutOfRange_False<typename OutOfRange_Low::source_type> Neither;
100
101 typedef typename OutOfRange_Low::can_be_true apply_low;
102 typedef typename OutOfRange_High::can_be_true apply_high;
103
104 typedef typename SkTMux<apply_low::value, apply_high::value,
105 Both, OutOfRange_Low, OutOfRange_High, Neither>::type type;
106 };
107
108 template<typename D, typename S, class OutOfRange_Low, class OutOfRange_High>
109 struct SkTRangeChecker {
110 /** This is the method which is called at runtime to do the range check. */
OutOfRangeSkTRangeChecker111 static bool OutOfRange(S s) {
112 typedef typename SkTCombineOutOfRange<OutOfRange_Low, OutOfRange_High>::type Combined;
113 return Combined::apply(s);
114 }
115 };
116
117 /** SkTFitsIn_Unsigned2Unsiged::type is an SkTRangeChecker with an OutOfRange(S s) method
118 * the implementation of which is tailored for the source and destination types.
119 * Assumes that S and D are unsigned integer types.
120 */
121 template<typename D, typename S> struct SkTFitsIn_Unsigned2Unsiged {
122 typedef SkTOutOfRange_False<S> OutOfRange_Low;
123 typedef SkTOutOfRange_GT_MaxD<D, S> OutOfRange_High;
124
125 typedef SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High> HighSideOnlyCheck;
126 typedef SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S> > NoCheck;
127
128 // If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check.
129 // This also protects the precondition of SkTOutOfRange_GT_MaxD.
130 typedef SkTHasMoreDigits<D, S> sourceFitsInDesitination;
131 typedef skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, HighSideOnlyCheck> type;
132 };
133
134 /** SkTFitsIn_Signed2Signed::type is an SkTRangeChecker with an OutOfRange(S s) method
135 * the implementation of which is tailored for the source and destination types.
136 * Assumes that S and D are signed integer types.
137 */
138 template<typename D, typename S> struct SkTFitsIn_Signed2Signed {
139 typedef SkTOutOfRange_LT_MinD<D, S> OutOfRange_Low;
140 typedef SkTOutOfRange_GT_MaxD<D, S> OutOfRange_High;
141
142 typedef SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High> FullCheck;
143 typedef SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S> > NoCheck;
144
145 // If std::numeric_limits<D>::digits >= std::numeric_limits<S>::digits, nothing to check.
146 // This also protects the precondition of SkTOutOfRange_LT_MinD and SkTOutOfRange_GT_MaxD.
147 typedef SkTHasMoreDigits<D, S> sourceFitsInDesitination;
148 typedef skstd::conditional_t<sourceFitsInDesitination::value, NoCheck, FullCheck> type;
149 };
150
151 /** SkTFitsIn_Signed2Unsigned::type is an SkTRangeChecker with an OutOfRange(S s) method
152 * the implementation of which is tailored for the source and destination types.
153 * Assumes that S is a signed integer type and D is an unsigned integer type.
154 */
155 template<typename D, typename S> struct SkTFitsIn_Signed2Unsigned {
156 typedef SkTOutOfRange_LT_Zero<D, S> OutOfRange_Low;
157 typedef SkTOutOfRange_GT_MaxD<D, S> OutOfRange_High;
158
159 typedef SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High> FullCheck;
160 typedef SkTRangeChecker<D, S, OutOfRange_Low, SkTOutOfRange_False<S> > LowSideOnlyCheck;
161
162 // If std::numeric_limits<D>::max() >= std::numeric_limits<S>::max(),
163 // no need to check the high side. (Until C++11, assume more digits means greater max.)
164 // This also protects the precondition of SkTOutOfRange_GT_MaxD.
165 typedef SkTHasMoreDigits<D, S> sourceCannotExceedDest;
166 typedef skstd::conditional_t<sourceCannotExceedDest::value, LowSideOnlyCheck, FullCheck> type;
167 };
168
169 /** SkTFitsIn_Unsigned2Signed::type is an SkTRangeChecker with an OutOfRange(S s) method
170 * the implementation of which is tailored for the source and destination types.
171 * Assumes that S is an usigned integer type and D is a signed integer type.
172 */
173 template<typename D, typename S> struct SkTFitsIn_Unsigned2Signed {
174 typedef SkTOutOfRange_False<S> OutOfRange_Low;
175 typedef SkTOutOfRange_GT_MaxD<D, S> OutOfRange_High;
176
177 typedef SkTRangeChecker<D, S, OutOfRange_Low, OutOfRange_High> HighSideOnlyCheck;
178 typedef SkTRangeChecker<D, S, SkTOutOfRange_False<S>, SkTOutOfRange_False<S> > NoCheck;
179
180 // If std::numeric_limits<D>::max() >= std::numeric_limits<S>::max(), nothing to check.
181 // (Until C++11, assume more digits means greater max.)
182 // This also protects the precondition of SkTOutOfRange_GT_MaxD.
183 typedef SkTHasMoreDigits<D, S> sourceCannotExceedDest;
184 typedef skstd::conditional_t<sourceCannotExceedDest::value, NoCheck, HighSideOnlyCheck> type;
185 };
186
187 /** SkTFitsIn::type is an SkTRangeChecker with an OutOfRange(S s) method
188 * the implementation of which is tailored for the source and destination types.
189 * Assumes that S and D are integer types.
190 */
191 template<typename D, typename S> struct SkTFitsIn {
192 // One of the following will be the 'selector' type.
193 typedef SkTFitsIn_Signed2Signed<D, S> S2S;
194 typedef SkTFitsIn_Signed2Unsigned<D, S> S2U;
195 typedef SkTFitsIn_Unsigned2Signed<D, S> U2S;
196 typedef SkTFitsIn_Unsigned2Unsiged<D, S> U2U;
197
198 typedef skstd::bool_constant<std::numeric_limits<S>::is_signed> S_is_signed;
199 typedef skstd::bool_constant<std::numeric_limits<D>::is_signed> D_is_signed;
200
201 typedef typename SkTMux<S_is_signed::value, D_is_signed::value,
202 S2S, S2U, U2S, U2U>::type selector;
203 // This type is an SkTRangeChecker.
204 typedef typename selector::type type;
205 };
206
207 } // namespace Private
208 } // namespace sktfitsin
209
210 /** Returns true if the integer source value 's' will fit in the integer destination type 'D'. */
SkTFitsIn(S s)211 template <typename D, typename S> inline bool SkTFitsIn(S s) {
212 static_assert(std::numeric_limits<S>::is_integer, "SkTFitsIn_source_must_be_integer");
213 static_assert(std::numeric_limits<D>::is_integer, "SkTFitsIn_destination_must_be_integer");
214
215 return !sktfitsin::Private::SkTFitsIn<D, S>::type::OutOfRange(s);
216 }
217
218 #endif
219