summaryrefslogtreecommitdiffstats
path: root/lib/intprops.h
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--lib/intprops.h335
1 files changed, 335 insertions, 0 deletions
diff --git a/lib/intprops.h b/lib/intprops.h
new file mode 100644
index 0000000..44b5e60
--- /dev/null
+++ b/lib/intprops.h
@@ -0,0 +1,335 @@
+/* intprops.h -- properties of integer types
+
+ Copyright (C) 2001-2023 Free Software Foundation, Inc.
+
+ This program is free software: you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published
+ by the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with this program. If not, see <https://www.gnu.org/licenses/>. */
+
+#ifndef _GL_INTPROPS_H
+#define _GL_INTPROPS_H
+
+#include "intprops-internal.h"
+
+/* The extra casts in the following macros work around compiler bugs,
+ e.g., in Cray C 5.0.3.0. */
+
+/* True if the arithmetic type T is an integer type. bool counts as
+ an integer. */
+#define TYPE_IS_INTEGER(t) ((t) 1.5 == 1)
+
+/* True if the real type T is signed. */
+#define TYPE_SIGNED(t) _GL_TYPE_SIGNED (t)
+
+/* Return 1 if the real expression E, after promotion, has a
+ signed or floating type. Do not evaluate E. */
+#define EXPR_SIGNED(e) _GL_EXPR_SIGNED (e)
+
+
+/* Minimum and maximum values for integer types and expressions. */
+
+/* The width in bits of the integer type or expression T.
+ Do not evaluate T. T must not be a bit-field expression.
+ Padding bits are not supported; this is checked at compile-time below. */
+#define TYPE_WIDTH(t) _GL_TYPE_WIDTH (t)
+
+/* The maximum and minimum values for the integer type T. */
+#define TYPE_MINIMUM(t) ((t) ~ TYPE_MAXIMUM (t))
+#define TYPE_MAXIMUM(t) \
+ ((t) (! TYPE_SIGNED (t) \
+ ? (t) -1 \
+ : ((((t) 1 << (TYPE_WIDTH (t) - 2)) - 1) * 2 + 1)))
+
+/* Bound on length of the string representing an unsigned integer
+ value representable in B bits. log10 (2.0) < 146/485. The
+ smallest value of B where this bound is not tight is 2621. */
+#define INT_BITS_STRLEN_BOUND(b) (((b) * 146 + 484) / 485)
+
+/* Bound on length of the string representing an integer type or expression T.
+ T must not be a bit-field expression.
+
+ Subtract 1 for the sign bit if T is signed, and then add 1 more for
+ a minus sign if needed.
+
+ Because _GL_SIGNED_TYPE_OR_EXPR sometimes returns 1 when its argument is
+ unsigned, this macro may overestimate the true bound by one byte when
+ applied to unsigned types of size 2, 4, 16, ... bytes. */
+#define INT_STRLEN_BOUND(t) \
+ (INT_BITS_STRLEN_BOUND (TYPE_WIDTH (t) - _GL_SIGNED_TYPE_OR_EXPR (t)) \
+ + _GL_SIGNED_TYPE_OR_EXPR (t))
+
+/* Bound on buffer size needed to represent an integer type or expression T,
+ including the terminating null. T must not be a bit-field expression. */
+#define INT_BUFSIZE_BOUND(t) (INT_STRLEN_BOUND (t) + 1)
+
+
+/* Range overflow checks.
+
+ The INT_<op>_RANGE_OVERFLOW macros return 1 if the corresponding C
+ operators overflow arithmetically when given the same arguments.
+ These macros do not rely on undefined or implementation-defined behavior.
+ Although their implementations are simple and straightforward,
+ they are harder to use and may be less efficient than the
+ INT_<op>_WRAPV, INT_<op>_OK, and INT_<op>_OVERFLOW macros described below.
+
+ Example usage:
+
+ long int i = ...;
+ long int j = ...;
+ if (INT_MULTIPLY_RANGE_OVERFLOW (i, j, LONG_MIN, LONG_MAX))
+ printf ("multiply would overflow");
+ else
+ printf ("product is %ld", i * j);
+
+ Restrictions on *_RANGE_OVERFLOW macros:
+
+ These macros do not check for all possible numerical problems or
+ undefined or unspecified behavior: they do not check for division
+ by zero, for bad shift counts, or for shifting negative numbers.
+
+ These macros may evaluate their arguments zero or multiple times,
+ so the arguments should not have side effects. The arithmetic
+ arguments (including the MIN and MAX arguments) must be of the same
+ integer type after the usual arithmetic conversions, and the type
+ must have minimum value MIN and maximum MAX. Unsigned types should
+ use a zero MIN of the proper type.
+
+ Because all arguments are subject to integer promotions, these
+ macros typically do not work on types narrower than 'int'.
+
+ These macros are tuned for constant MIN and MAX. For commutative
+ operations such as A + B, they are also tuned for constant B. */
+
+/* Return 1 if A + B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. */
+#define INT_ADD_RANGE_OVERFLOW(a, b, min, max) \
+ ((b) < 0 \
+ ? (a) < (min) - (b) \
+ : (max) - (b) < (a))
+
+/* Return 1 if A - B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. */
+#define INT_SUBTRACT_RANGE_OVERFLOW(a, b, min, max) \
+ ((b) < 0 \
+ ? (max) + (b) < (a) \
+ : (a) < (min) + (b))
+
+/* Return 1 if - A would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. */
+#define INT_NEGATE_RANGE_OVERFLOW(a, min, max) \
+ _GL_INT_NEGATE_RANGE_OVERFLOW (a, min, max)
+
+/* Return 1 if A * B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. Avoid && and || as they tickle
+ bugs in Sun C 5.11 2010/08/13 and other compilers; see
+ <https://lists.gnu.org/r/bug-gnulib/2011-05/msg00401.html>. */
+#define INT_MULTIPLY_RANGE_OVERFLOW(a, b, min, max) \
+ ((b) < 0 \
+ ? ((a) < 0 \
+ ? (a) < (max) / (b) \
+ : (b) == -1 \
+ ? 0 \
+ : (min) / (b) < (a)) \
+ : (b) == 0 \
+ ? 0 \
+ : ((a) < 0 \
+ ? (a) < (min) / (b) \
+ : (max) / (b) < (a)))
+
+/* Return 1 if A / B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. Do not check for division by zero. */
+#define INT_DIVIDE_RANGE_OVERFLOW(a, b, min, max) \
+ ((min) < 0 && (b) == -1 && (a) < - (max))
+
+/* Return 1 if A % B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. Do not check for division by zero.
+ Mathematically, % should never overflow, but on x86-like hosts
+ INT_MIN % -1 traps, and the C standard permits this, so treat this
+ as an overflow too. */
+#define INT_REMAINDER_RANGE_OVERFLOW(a, b, min, max) \
+ INT_DIVIDE_RANGE_OVERFLOW (a, b, min, max)
+
+/* Return 1 if A << B would overflow in [MIN,MAX] arithmetic.
+ See above for restrictions. Here, MIN and MAX are for A only, and B need
+ not be of the same type as the other arguments. The C standard says that
+ behavior is undefined for shifts unless 0 <= B < wordwidth, and that when
+ A is negative then A << B has undefined behavior and A >> B has
+ implementation-defined behavior, but do not check these other
+ restrictions. */
+#define INT_LEFT_SHIFT_RANGE_OVERFLOW(a, b, min, max) \
+ ((a) < 0 \
+ ? (a) < (min) >> (b) \
+ : (max) >> (b) < (a))
+
+/* The _GL*_OVERFLOW macros have the same restrictions as the
+ *_RANGE_OVERFLOW macros, except that they do not assume that operands
+ (e.g., A and B) have the same type as MIN and MAX. Instead, they assume
+ that the result (e.g., A + B) has that type. */
+#if _GL_HAS_BUILTIN_OVERFLOW_P
+# define _GL_ADD_OVERFLOW(a, b, min, max) \
+ __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0)
+# define _GL_SUBTRACT_OVERFLOW(a, b, min, max) \
+ __builtin_sub_overflow_p (a, b, (__typeof__ ((a) - (b))) 0)
+# define _GL_MULTIPLY_OVERFLOW(a, b, min, max) \
+ __builtin_mul_overflow_p (a, b, (__typeof__ ((a) * (b))) 0)
+#else
+# define _GL_ADD_OVERFLOW(a, b, min, max) \
+ ((min) < 0 ? INT_ADD_RANGE_OVERFLOW (a, b, min, max) \
+ : (a) < 0 ? (b) <= (a) + (b) \
+ : (b) < 0 ? (a) <= (a) + (b) \
+ : (a) + (b) < (b))
+# define _GL_SUBTRACT_OVERFLOW(a, b, min, max) \
+ ((min) < 0 ? INT_SUBTRACT_RANGE_OVERFLOW (a, b, min, max) \
+ : (a) < 0 ? 1 \
+ : (b) < 0 ? (a) - (b) <= (a) \
+ : (a) < (b))
+# define _GL_MULTIPLY_OVERFLOW(a, b, min, max) \
+ (((min) == 0 && (((a) < 0 && 0 < (b)) || ((b) < 0 && 0 < (a)))) \
+ || INT_MULTIPLY_RANGE_OVERFLOW (a, b, min, max))
+#endif
+#define _GL_DIVIDE_OVERFLOW(a, b, min, max) \
+ ((min) < 0 ? (b) == _GL_INT_NEGATE_CONVERT (min, 1) && (a) < - (max) \
+ : (a) < 0 ? (b) <= (a) + (b) - 1 \
+ : (b) < 0 && (a) + (b) <= (a))
+#define _GL_REMAINDER_OVERFLOW(a, b, min, max) \
+ ((min) < 0 ? (b) == _GL_INT_NEGATE_CONVERT (min, 1) && (a) < - (max) \
+ : (a) < 0 ? (a) % (b) != ((max) - (b) + 1) % (b) \
+ : (b) < 0 && ! _GL_UNSIGNED_NEG_MULTIPLE (a, b, max))
+
+/* Return a nonzero value if A is a mathematical multiple of B, where
+ A is unsigned, B is negative, and MAX is the maximum value of A's
+ type. A's type must be the same as (A % B)'s type. Normally (A %
+ -B == 0) suffices, but things get tricky if -B would overflow. */
+#define _GL_UNSIGNED_NEG_MULTIPLE(a, b, max) \
+ (((b) < -_GL_SIGNED_INT_MAXIMUM (b) \
+ ? (_GL_SIGNED_INT_MAXIMUM (b) == (max) \
+ ? (a) \
+ : (a) % (_GL_INT_CONVERT (a, _GL_SIGNED_INT_MAXIMUM (b)) + 1)) \
+ : (a) % - (b)) \
+ == 0)
+
+/* Check for integer overflow, and report low order bits of answer.
+
+ The INT_<op>_OVERFLOW macros return 1 if the corresponding C operators
+ might not yield numerically correct answers due to arithmetic overflow.
+ The INT_<op>_WRAPV macros compute the low-order bits of the sum,
+ difference, and product of two C integers, and return 1 if these
+ low-order bits are not numerically correct.
+ These macros work correctly on all known practical hosts, and do not rely
+ on undefined behavior due to signed arithmetic overflow.
+
+ Example usage, assuming A and B are long int:
+
+ if (INT_MULTIPLY_OVERFLOW (a, b))
+ printf ("result would overflow\n");
+ else
+ printf ("result is %ld (no overflow)\n", a * b);
+
+ Example usage with WRAPV flavor:
+
+ long int result;
+ bool overflow = INT_MULTIPLY_WRAPV (a, b, &result);
+ printf ("result is %ld (%s)\n", result,
+ overflow ? "after overflow" : "no overflow");
+
+ Restrictions on these macros:
+
+ These macros do not check for all possible numerical problems or
+ undefined or unspecified behavior: they do not check for division
+ by zero, for bad shift counts, or for shifting negative numbers.
+
+ These macros may evaluate their arguments zero or multiple times, so the
+ arguments should not have side effects.
+
+ The WRAPV macros are not constant expressions. They support only
+ +, binary -, and *.
+
+ Because the WRAPV macros convert the result, they report overflow
+ in different circumstances than the OVERFLOW macros do. For
+ example, in the typical case with 16-bit 'short' and 32-bit 'int',
+ if A, B and *R are all of type 'short' then INT_ADD_OVERFLOW (A, B)
+ returns false because the addition cannot overflow after A and B
+ are converted to 'int', whereas INT_ADD_WRAPV (A, B, R) returns
+ true or false depending on whether the sum fits into 'short'.
+
+ These macros are tuned for their last input argument being a constant.
+
+ A, B, and *R should be integers; they need not be the same type,
+ and they need not be all signed or all unsigned.
+ However, none of the integer types should be bit-precise,
+ and *R's type should not be char, bool, or an enumeration type.
+
+ Return 1 if the integer expressions A * B, A - B, -A, A * B, A / B,
+ A % B, and A << B would overflow, respectively. */
+
+#define INT_ADD_OVERFLOW(a, b) \
+ _GL_BINARY_OP_OVERFLOW (a, b, _GL_ADD_OVERFLOW)
+#define INT_SUBTRACT_OVERFLOW(a, b) \
+ _GL_BINARY_OP_OVERFLOW (a, b, _GL_SUBTRACT_OVERFLOW)
+#define INT_NEGATE_OVERFLOW(a) _GL_INT_NEGATE_OVERFLOW (a)
+#define INT_MULTIPLY_OVERFLOW(a, b) \
+ _GL_BINARY_OP_OVERFLOW (a, b, _GL_MULTIPLY_OVERFLOW)
+#define INT_DIVIDE_OVERFLOW(a, b) \
+ _GL_BINARY_OP_OVERFLOW (a, b, _GL_DIVIDE_OVERFLOW)
+#define INT_REMAINDER_OVERFLOW(a, b) \
+ _GL_BINARY_OP_OVERFLOW (a, b, _GL_REMAINDER_OVERFLOW)
+#define INT_LEFT_SHIFT_OVERFLOW(a, b) \
+ INT_LEFT_SHIFT_RANGE_OVERFLOW (a, b, \
+ _GL_INT_MINIMUM (a), _GL_INT_MAXIMUM (a))
+
+/* Return 1 if the expression A <op> B would overflow,
+ where OP_RESULT_OVERFLOW (A, B, MIN, MAX) does the actual test,
+ assuming MIN and MAX are the minimum and maximum for the result type.
+ Arguments should be free of side effects. */
+#define _GL_BINARY_OP_OVERFLOW(a, b, op_result_overflow) \
+ op_result_overflow (a, b, \
+ _GL_INT_MINIMUM (_GL_INT_CONVERT (a, b)), \
+ _GL_INT_MAXIMUM (_GL_INT_CONVERT (a, b)))
+
+/* Store the low-order bits of A + B, A - B, A * B, respectively, into *R.
+ Return 1 if the result overflows. See above for restrictions. */
+#define INT_ADD_WRAPV(a, b, r) _GL_INT_ADD_WRAPV (a, b, r)
+#define INT_SUBTRACT_WRAPV(a, b, r) _GL_INT_SUBTRACT_WRAPV (a, b, r)
+#define INT_MULTIPLY_WRAPV(a, b, r) _GL_INT_MULTIPLY_WRAPV (a, b, r)
+
+/* The following macros compute A + B, A - B, and A * B, respectively.
+ If no overflow occurs, they set *R to the result and return 1;
+ otherwise, they return 0 and may modify *R.
+
+ Example usage:
+
+ long int result;
+ if (INT_ADD_OK (a, b, &result))
+ printf ("result is %ld\n", result);
+ else
+ printf ("overflow\n");
+
+ A, B, and *R should be integers; they need not be the same type,
+ and they need not be all signed or all unsigned.
+ However, none of the integer types should be bit-precise,
+ and *R's type should not be char, bool, or an enumeration type.
+
+ These macros work correctly on all known practical hosts, and do not rely
+ on undefined behavior due to signed arithmetic overflow.
+
+ These macros are not constant expressions.
+
+ These macros may evaluate their arguments zero or multiple times, so the
+ arguments should not have side effects.
+
+ These macros are tuned for B being a constant. */
+
+#define INT_ADD_OK(a, b, r) (! INT_ADD_WRAPV (a, b, r))
+#define INT_SUBTRACT_OK(a, b, r) (! INT_SUBTRACT_WRAPV (a, b, r))
+#define INT_MULTIPLY_OK(a, b, r) (! INT_MULTIPLY_WRAPV (a, b, r))
+
+#endif /* _GL_INTPROPS_H */