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- lib/intprops.h
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1 /* intprops.h -- properties of integer types
2
3 Copyright (C) 2001-2024 Free Software Foundation, Inc.
4
5 This program is free software: you can redistribute it and/or modify it
6 under the terms of the GNU Lesser General Public License as published
7 by the Free Software Foundation; either version 2.1 of the License, or
8 (at your option) any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 #ifndef _GL_INTPROPS_H
19 #define _GL_INTPROPS_H
20
21 #include "intprops-internal.h"
22
23 /* The extra casts in the following macros work around compiler bugs,
24 e.g., in Cray C 5.0.3.0. */
25
26 /* True if the arithmetic type T is an integer type. bool counts as
27 an integer. */
28 #define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
29
30 /* True if the real type T is signed. */
31 #define TYPE_SIGNED(t) _GL_TYPE_SIGNED (t)
32
33 /* Return 1 if the real expression E, after promotion, has a
34 signed or floating type. Do not evaluate E. */
35 #define EXPR_SIGNED(e) _GL_EXPR_SIGNED (e)
36
37
38 /* Minimum and maximum values for integer types and expressions. */
39
40 /* The width in bits of the integer type or expression T.
41 Do not evaluate T. T must not be a bit-field expression.
42 Padding bits are not supported; this is checked at compile-time below. */
43 #define TYPE_WIDTH(t) _GL_TYPE_WIDTH (t)
44
45 /* The maximum and minimum values for the integer type T. */
46 #define TYPE_MINIMUM(t) ((t) ~ TYPE_MAXIMUM (t))
47 #define TYPE_MAXIMUM(t) \
48 ((t) (! TYPE_SIGNED (t) \
49 ? (t) -1 \
50 : ((((t) 1 << (TYPE_WIDTH (t) - 2)) - 1) * 2 + 1)))
51
52 /* Bound on length of the string representing an unsigned integer
53 value representable in B bits. log10 (2.0) < 146/485. The
54 smallest value of B where this bound is not tight is 2621. */
55 #define INT_BITS_STRLEN_BOUND(b) (((b) * 146 + 484) / 485)
56
57 /* Bound on length of the string representing an integer type or expression T.
58 T must not be a bit-field expression.
59
60 Subtract 1 for the sign bit if T is signed, and then add 1 more for
61 a minus sign if needed.
62
63 Because _GL_SIGNED_TYPE_OR_EXPR sometimes returns 1 when its argument is
64 unsigned, this macro may overestimate the true bound by one byte when
65 applied to unsigned types of size 2, 4, 16, ... bytes. */
66 #define INT_STRLEN_BOUND(t) \
67 (INT_BITS_STRLEN_BOUND (TYPE_WIDTH (t) - _GL_SIGNED_TYPE_OR_EXPR (t)) \
68 + _GL_SIGNED_TYPE_OR_EXPR (t))
69
70 /* Bound on buffer size needed to represent an integer type or expression T,
71 including the terminating null. T must not be a bit-field expression. */
72 #define INT_BUFSIZE_BOUND(t) (INT_STRLEN_BOUND (t) + 1)
73
74
75 /* Range overflow checks.
76
77 The INT_<op>_RANGE_OVERFLOW macros return 1 if the corresponding C
78 operators overflow arithmetically when given the same arguments.
79 These macros do not rely on undefined or implementation-defined behavior.
80 Although their implementations are simple and straightforward,
81 they are harder to use and may be less efficient than the
82 INT_<op>_WRAPV, INT_<op>_OK, and INT_<op>_OVERFLOW macros described below.
83
84 Example usage:
85
86 long int i = ...;
87 long int j = ...;
88 if (INT_MULTIPLY_RANGE_OVERFLOW (i, j, LONG_MIN, LONG_MAX))
89 printf ("multiply would overflow");
90 else
91 printf ("product is %ld", i * j);
92
93 Restrictions on *_RANGE_OVERFLOW macros:
94
95 These macros do not check for all possible numerical problems or
96 undefined or unspecified behavior: they do not check for division
97 by zero, for bad shift counts, or for shifting negative numbers.
98
99 These macros may evaluate their arguments zero or multiple times,
100 so the arguments should not have side effects. The arithmetic
101 arguments (including the MIN and MAX arguments) must be of the same
102 integer type after the usual arithmetic conversions, and the type
103 must have minimum value MIN and maximum MAX. Unsigned types should
104 use a zero MIN of the proper type.
105
106 Because all arguments are subject to integer promotions, these
107 macros typically do not work on types narrower than 'int'.
108
109 These macros are tuned for constant MIN and MAX. For commutative
110 operations such as A + B, they are also tuned for constant B. */
111
112 /* Return 1 if A + B would overflow in [MIN,MAX] arithmetic.
113 See above for restrictions. */
114 #define INT_ADD_RANGE_OVERFLOW(a, b, min, max) \
115 ((b) < 0 \
116 ? (a) < (min) - (b) \
117 : (max) - (b) < (a))
118
119 /* Return 1 if A - B would overflow in [MIN,MAX] arithmetic.
120 See above for restrictions. */
121 #define INT_SUBTRACT_RANGE_OVERFLOW(a, b, min, max) \
122 ((b) < 0 \
123 ? (max) + (b) < (a) \
124 : (a) < (min) + (b))
125
126 /* Return 1 if - A would overflow in [MIN,MAX] arithmetic.
127 See above for restrictions. */
128 #define INT_NEGATE_RANGE_OVERFLOW(a, min, max) \
129 _GL_INT_NEGATE_RANGE_OVERFLOW (a, min, max)
130
131 /* Return 1 if A * B would overflow in [MIN,MAX] arithmetic.
132 See above for restrictions. Avoid && and || as they tickle
133 bugs in Sun C 5.11 2010/08/13 and other compilers; see
134 <https://lists.gnu.org/r/bug-gnulib/2011-05/msg00401.html>. */
135 #define INT_MULTIPLY_RANGE_OVERFLOW(a, b, min, max) \
136 ((b) < 0 \
137 ? ((a) < 0 \
138 ? (a) < (max) / (b) \
139 : (b) == -1 \
140 ? 0 \
141 : (min) / (b) < (a)) \
142 : (b) == 0 \
143 ? 0 \
144 : ((a) < 0 \
145 ? (a) < (min) / (b) \
146 : (max) / (b) < (a)))
147
148 /* Return 1 if A / B would overflow in [MIN,MAX] arithmetic.
149 See above for restrictions. Do not check for division by zero. */
150 #define INT_DIVIDE_RANGE_OVERFLOW(a, b, min, max) \
151 ((min) < 0 && (b) == -1 && (a) < - (max))
152
153 /* Return 1 if A % B would overflow in [MIN,MAX] arithmetic.
154 See above for restrictions. Do not check for division by zero.
155 Mathematically, % should never overflow, but on x86-like hosts
156 INT_MIN % -1 traps, and the C standard permits this, so treat this
157 as an overflow too. */
158 #define INT_REMAINDER_RANGE_OVERFLOW(a, b, min, max) \
159 INT_DIVIDE_RANGE_OVERFLOW (a, b, min, max)
160
161 /* Return 1 if A << B would overflow in [MIN,MAX] arithmetic.
162 See above for restrictions. Here, MIN and MAX are for A only, and B need
163 not be of the same type as the other arguments. The C standard says that
164 behavior is undefined for shifts unless 0 <= B < wordwidth, and that when
165 A is negative then A << B has undefined behavior and A >> B has
166 implementation-defined behavior, but do not check these other
167 restrictions. */
168 #define INT_LEFT_SHIFT_RANGE_OVERFLOW(a, b, min, max) \
169 ((a) < 0 \
170 ? (a) < (min) >> (b) \
171 : (max) >> (b) < (a))
172
173 /* The _GL*_OVERFLOW macros have the same restrictions as the
174 *_RANGE_OVERFLOW macros, except that they do not assume that operands
175 (e.g., A and B) have the same type as MIN and MAX. Instead, they assume
176 that the result (e.g., A + B) has that type. */
177 #if _GL_HAS_BUILTIN_OVERFLOW_P
178 # define _GL_ADD_OVERFLOW(a, b, min, max) \
179 __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0)
180 # define _GL_SUBTRACT_OVERFLOW(a, b, min, max) \
181 __builtin_sub_overflow_p (a, b, (__typeof__ ((a) - (b))) 0)
182 # define _GL_MULTIPLY_OVERFLOW(a, b, min, max) \
183 __builtin_mul_overflow_p (a, b, (__typeof__ ((a) * (b))) 0)
184 #else
185 # define _GL_ADD_OVERFLOW(a, b, min, max) \
186 ((min) < 0 ? INT_ADD_RANGE_OVERFLOW (a, b, min, max) \
187 : (a) < 0 ? (b) <= (a) + (b) \
188 : (b) < 0 ? (a) <= (a) + (b) \
189 : (a) + (b) < (b))
190 # define _GL_SUBTRACT_OVERFLOW(a, b, min, max) \
191 ((min) < 0 ? INT_SUBTRACT_RANGE_OVERFLOW (a, b, min, max) \
192 : (a) < 0 ? 1 \
193 : (b) < 0 ? (a) - (b) <= (a) \
194 : (a) < (b))
195 # define _GL_MULTIPLY_OVERFLOW(a, b, min, max) \
196 (((min) == 0 && (((a) < 0 && 0 < (b)) || ((b) < 0 && 0 < (a)))) \
197 || INT_MULTIPLY_RANGE_OVERFLOW (a, b, min, max))
198 #endif
199 #define _GL_DIVIDE_OVERFLOW(a, b, min, max) \
200 ((min) < 0 ? (b) == _GL_INT_NEGATE_CONVERT (min, 1) && (a) < - (max) \
201 : (a) < 0 ? (b) <= (a) + (b) - 1 \
202 : (b) < 0 && (a) + (b) <= (a))
203 #define _GL_REMAINDER_OVERFLOW(a, b, min, max) \
204 ((min) < 0 ? (b) == _GL_INT_NEGATE_CONVERT (min, 1) && (a) < - (max) \
205 : (a) < 0 ? (a) % (b) != ((max) - (b) + 1) % (b) \
206 : (b) < 0 && ! _GL_UNSIGNED_NEG_MULTIPLE (a, b, max))
207
208 /* Return a nonzero value if A is a mathematical multiple of B, where
209 A is unsigned, B is negative, and MAX is the maximum value of A's
210 type. A's type must be the same as (A % B)'s type. Normally (A %
211 -B == 0) suffices, but things get tricky if -B would overflow. */
212 #define _GL_UNSIGNED_NEG_MULTIPLE(a, b, max) \
213 (((b) < -_GL_SIGNED_INT_MAXIMUM (b) \
214 ? (_GL_SIGNED_INT_MAXIMUM (b) == (max) \
215 ? (a) \
216 : (a) % (_GL_INT_CONVERT (a, _GL_SIGNED_INT_MAXIMUM (b)) + 1)) \
217 : (a) % - (b)) \
218 == 0)
219
220 /* Check for integer overflow, and report low order bits of answer.
221
222 The INT_<op>_OVERFLOW macros return 1 if the corresponding C operators
223 might not yield numerically correct answers due to arithmetic overflow.
224 The INT_<op>_WRAPV macros compute the low-order bits of the sum,
225 difference, and product of two C integers, and return 1 if these
226 low-order bits are not numerically correct.
227 These macros work correctly on all known practical hosts, and do not rely
228 on undefined behavior due to signed arithmetic overflow.
229
230 Example usage, assuming A and B are long int:
231
232 if (INT_MULTIPLY_OVERFLOW (a, b))
233 printf ("result would overflow\n");
234 else
235 printf ("result is %ld (no overflow)\n", a * b);
236
237 Example usage with WRAPV flavor:
238
239 long int result;
240 bool overflow = INT_MULTIPLY_WRAPV (a, b, &result);
241 printf ("result is %ld (%s)\n", result,
242 overflow ? "after overflow" : "no overflow");
243
244 Restrictions on these macros:
245
246 These macros do not check for all possible numerical problems or
247 undefined or unspecified behavior: they do not check for division
248 by zero, for bad shift counts, or for shifting negative numbers.
249
250 These macros may evaluate their arguments zero or multiple times, so the
251 arguments should not have side effects.
252
253 The WRAPV macros are not constant expressions. They support only
254 +, binary -, and *.
255
256 Because the WRAPV macros convert the result, they report overflow
257 in different circumstances than the OVERFLOW macros do. For
258 example, in the typical case with 16-bit 'short' and 32-bit 'int',
259 if A, B and *R are all of type 'short' then INT_ADD_OVERFLOW (A, B)
260 returns false because the addition cannot overflow after A and B
261 are converted to 'int', whereas INT_ADD_WRAPV (A, B, R) returns
262 true or false depending on whether the sum fits into 'short'.
263
264 These macros are tuned for their last input argument being a constant.
265
266 A, B, and *R should be integers; they need not be the same type,
267 and they need not be all signed or all unsigned.
268 However, none of the integer types should be bit-precise,
269 and *R's type should not be char, bool, or an enumeration type.
270
271 Return 1 if the integer expressions A * B, A - B, -A, A * B, A / B,
272 A % B, and A << B would overflow, respectively. */
273
274 #define INT_ADD_OVERFLOW(a, b) \
275 _GL_BINARY_OP_OVERFLOW (a, b, _GL_ADD_OVERFLOW)
276 #define INT_SUBTRACT_OVERFLOW(a, b) \
277 _GL_BINARY_OP_OVERFLOW (a, b, _GL_SUBTRACT_OVERFLOW)
278 #define INT_NEGATE_OVERFLOW(a) _GL_INT_NEGATE_OVERFLOW (a)
279 #define INT_MULTIPLY_OVERFLOW(a, b) \
280 _GL_BINARY_OP_OVERFLOW (a, b, _GL_MULTIPLY_OVERFLOW)
281 #define INT_DIVIDE_OVERFLOW(a, b) \
282 _GL_BINARY_OP_OVERFLOW (a, b, _GL_DIVIDE_OVERFLOW)
283 #define INT_REMAINDER_OVERFLOW(a, b) \
284 _GL_BINARY_OP_OVERFLOW (a, b, _GL_REMAINDER_OVERFLOW)
285 #define INT_LEFT_SHIFT_OVERFLOW(a, b) \
286 INT_LEFT_SHIFT_RANGE_OVERFLOW (a, b, \
287 _GL_INT_MINIMUM (a), _GL_INT_MAXIMUM (a))
288
289 /* Return 1 if the expression A <op> B would overflow,
290 where OP_RESULT_OVERFLOW (A, B, MIN, MAX) does the actual test,
291 assuming MIN and MAX are the minimum and maximum for the result type.
292 Arguments should be free of side effects. */
293 #define _GL_BINARY_OP_OVERFLOW(a, b, op_result_overflow) \
294 op_result_overflow (a, b, \
295 _GL_INT_MINIMUM (_GL_INT_CONVERT (a, b)), \
296 _GL_INT_MAXIMUM (_GL_INT_CONVERT (a, b)))
297
298 /* Store the low-order bits of A + B, A - B, A * B, respectively, into *R.
299 Return 1 if the result overflows. See above for restrictions. */
300 #define INT_ADD_WRAPV(a, b, r) _GL_INT_ADD_WRAPV (a, b, r)
301 #define INT_SUBTRACT_WRAPV(a, b, r) _GL_INT_SUBTRACT_WRAPV (a, b, r)
302 #define INT_MULTIPLY_WRAPV(a, b, r) _GL_INT_MULTIPLY_WRAPV (a, b, r)
303
304 /* The following macros compute A + B, A - B, and A * B, respectively.
305 If no overflow occurs, they set *R to the result and return 1;
306 otherwise, they return 0 and may modify *R.
307
308 Example usage:
309
310 long int result;
311 if (INT_ADD_OK (a, b, &result))
312 printf ("result is %ld\n", result);
313 else
314 printf ("overflow\n");
315
316 A, B, and *R should be integers; they need not be the same type,
317 and they need not be all signed or all unsigned.
318 However, none of the integer types should be bit-precise,
319 and *R's type should not be char, bool, or an enumeration type.
320
321 These macros work correctly on all known practical hosts, and do not rely
322 on undefined behavior due to signed arithmetic overflow.
323
324 These macros are not constant expressions.
325
326 These macros may evaluate their arguments zero or multiple times, so the
327 arguments should not have side effects.
328
329 These macros are tuned for B being a constant. */
330
331 #define INT_ADD_OK(a, b, r) (! INT_ADD_WRAPV (a, b, r))
332 #define INT_SUBTRACT_OK(a, b, r) (! INT_SUBTRACT_WRAPV (a, b, r))
333 #define INT_MULTIPLY_OK(a, b, r) (! INT_MULTIPLY_WRAPV (a, b, r))
334
335 #endif /* _GL_INTPROPS_H */
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