diff options
Diffstat (limited to 'lib/intprops.h')
| -rw-r--r-- | lib/intprops.h | 144 |
1 files changed, 126 insertions, 18 deletions
diff --git a/lib/intprops.h b/lib/intprops.h index f85ccad..8fff86d 100644 --- a/lib/intprops.h +++ b/lib/intprops.h @@ -22,8 +22,7 @@ #include <limits.h> -/* Return an integer value, converted to the same type as the integer - expression E after integer type promotion. V is the unconverted value. */ +/* Return a value with the common real type of E and V and the value of V. */ #define _GL_INT_CONVERT(e, v) (0 * (e) + (v)) /* Act like _GL_INT_CONVERT (E, -V) but work around a bug in IRIX 6.5 cc; see @@ -48,12 +47,12 @@ /* True if the signed integer expression E uses two's complement. */ #define _GL_INT_TWOS_COMPLEMENT(e) (~ _GL_INT_CONVERT (e, 0) == -1) -/* True if the arithmetic type T is signed. */ +/* True if the real type T is signed. */ #define TYPE_SIGNED(t) (! ((t) 0 < (t) -1)) -/* Return 1 if the integer expression E, after integer promotion, has - a signed type. */ -#define _GL_INT_SIGNED(e) (_GL_INT_NEGATE_CONVERT (e, 1) < 0) +/* Return 1 if the real expression E, after promotion, has a + signed or floating type. */ +#define EXPR_SIGNED(e) (_GL_INT_NEGATE_CONVERT (e, 1) < 0) /* Minimum and maximum values for integer types and expressions. These @@ -76,11 +75,11 @@ /* The maximum and minimum values for the type of the expression E, after integer promotion. E should not have side effects. */ #define _GL_INT_MINIMUM(e) \ - (_GL_INT_SIGNED (e) \ + (EXPR_SIGNED (e) \ ? - _GL_INT_TWOS_COMPLEMENT (e) - _GL_SIGNED_INT_MAXIMUM (e) \ : _GL_INT_CONVERT (e, 0)) #define _GL_INT_MAXIMUM(e) \ - (_GL_INT_SIGNED (e) \ + (EXPR_SIGNED (e) \ ? _GL_SIGNED_INT_MAXIMUM (e) \ : _GL_INT_NEGATE_CONVERT (e, 1)) #define _GL_SIGNED_INT_MAXIMUM(e) \ @@ -263,22 +262,28 @@ : (a) % - (b)) \ == 0) - -/* Integer overflow checks. +/* 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. - They work correctly on all known practical hosts, and do not rely + The INT_<op>_WRAPV macros also store the low-order bits of the answer. + These macros work correctly on all known practical hosts, and do not rely on undefined behavior due to signed arithmetic overflow. - Example usage: + Example usage, assuming A and B are long int: - long int i = ...; - long int j = ...; - if (INT_MULTIPLY_OVERFLOW (i, j)) - printf ("multiply would overflow"); - else - printf ("product is %ld", i * j); + long int result = INT_MULTIPLY_WRAPV (a, b); + printf ("result is %ld (%s)\n", result, + INT_MULTIPLY_OVERFLOW (a, b) ? "after overflow" : "no overflow"); + + 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 @@ -287,6 +292,9 @@ 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 *. The result type must be signed. + These macros are tuned for their last argument being a constant. Return 1 if the integer expressions A * B, A - B, -A, A * B, A / B, @@ -317,4 +325,104 @@ _GL_INT_MINIMUM (0 * (b) + (a)), \ _GL_INT_MAXIMUM (0 * (b) + (a))) +/* Compute A + B, A - B, A * B, respectively, storing the result into *R. + Return 1 if the result overflows. See above for restrictions. */ +#define INT_ADD_WRAPV(a, b, r) \ + _GL_INT_OP_WRAPV (a, b, r, +, __builtin_add_overflow, INT_ADD_OVERFLOW) +#define INT_SUBTRACT_WRAPV(a, b, r) \ + _GL_INT_OP_WRAPV (a, b, r, -, __builtin_sub_overflow, INT_SUBTRACT_OVERFLOW) +#define INT_MULTIPLY_WRAPV(a, b, r) \ + _GL_INT_OP_WRAPV (a, b, r, *, __builtin_mul_overflow, INT_MULTIPLY_OVERFLOW) + +#ifndef __has_builtin +# define __has_builtin(x) 0 +#endif + +/* Nonzero if this compiler has GCC bug 68193 or Clang bug 25390. See: + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68193 + https://llvm.org/bugs/show_bug.cgi?id=25390 + For now, assume all versions of GCC-like compilers generate bogus + warnings for _Generic. This matters only for older compilers that + lack __builtin_add_overflow. */ +#if __GNUC__ +# define _GL__GENERIC_BOGUS 1 +#else +# define _GL__GENERIC_BOGUS 0 +#endif + +/* Store A <op> B into *R, where OP specifies the operation. + BUILTIN is the builtin operation, and OVERFLOW the overflow predicate. + See above for restrictions. */ +#if 5 <= __GNUC__ || __has_builtin (__builtin_add_overflow) +# define _GL_INT_OP_WRAPV(a, b, r, op, builtin, overflow) builtin (a, b, r) +#elif 201112 <= __STDC_VERSION__ && !_GL__GENERIC_BOGUS +# define _GL_INT_OP_WRAPV(a, b, r, op, builtin, overflow) \ + (_Generic \ + (*(r), \ + signed char: \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned char, \ + signed char, SCHAR_MIN, SCHAR_MAX), \ + short int: \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned short int, \ + short int, SHRT_MIN, SHRT_MAX), \ + int: \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int, \ + int, INT_MIN, INT_MAX), \ + long int: \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long int, \ + long int, LONG_MIN, LONG_MAX), \ + long long int: \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long long int, \ + long long int, LLONG_MIN, LLONG_MAX))) +#else +# define _GL_INT_OP_WRAPV(a, b, r, op, builtin, overflow) \ + (sizeof *(r) == sizeof (signed char) \ + ? _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned char, \ + signed char, SCHAR_MIN, SCHAR_MAX) \ + : sizeof *(r) == sizeof (short int) \ + ? _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned short int, \ + short int, SHRT_MIN, SHRT_MAX) \ + : sizeof *(r) == sizeof (int) \ + ? _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned int, \ + int, INT_MIN, INT_MAX) \ + : _GL_INT_OP_WRAPV_LONGISH(a, b, r, op, overflow)) +# ifdef LLONG_MAX +# define _GL_INT_OP_WRAPV_LONGISH(a, b, r, op, overflow) \ + (sizeof *(r) == sizeof (long int) \ + ? _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long int, \ + long int, LONG_MIN, LONG_MAX) \ + : _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long long int, \ + long long int, LLONG_MIN, LLONG_MAX)) +# else +# define _GL_INT_OP_WRAPV_LONGISH(a, b, r, op, overflow) \ + _GL_INT_OP_CALC (a, b, r, op, overflow, unsigned long int, \ + long int, LONG_MIN, LONG_MAX)) +# endif +#endif + +/* Store the low-order bits of A <op> B into *R, where the operation + is given by OP. Use the unsigned type UT for calculation to avoid + overflow problems. *R's type is T, with extremal values TMIN and + TMAX. T must be a signed integer type. */ +#define _GL_INT_OP_CALC(a, b, r, op, overflow, ut, t, tmin, tmax) \ + (sizeof ((a) op (b)) < sizeof (t) \ + ? _GL_INT_OP_CALC1 ((t) (a), (t) (b), r, op, overflow, ut, t, tmin, tmax) \ + : _GL_INT_OP_CALC1 (a, b, r, op, overflow, ut, t, tmin, tmax)) +#define _GL_INT_OP_CALC1(a, b, r, op, overflow, ut, t, tmin, tmax) \ + ((overflow (a, b) \ + || (EXPR_SIGNED ((a) op (b)) && ((a) op (b)) < (tmin)) \ + || (tmax) < ((a) op (b))) \ + ? (*(r) = _GL_INT_OP_WRAPV_VIA_UNSIGNED (a, b, op, ut, t, tmin, tmax), 1) \ + : (*(r) = _GL_INT_OP_WRAPV_VIA_UNSIGNED (a, b, op, ut, t, tmin, tmax), 0)) + +/* Return A <op> B, where the operation is given by OP. Use the + unsigned type UT for calculation to avoid overflow problems. + Convert the result to type T without overflow by subtracting TMIN + from large values before converting, and adding it afterwards. + Compilers can optimize all the operations except OP. */ +#define _GL_INT_OP_WRAPV_VIA_UNSIGNED(a, b, op, ut, t, tmin, tmax) \ + (((ut) (a) op (ut) (b)) <= (tmax) \ + ? (t) ((ut) (a) op (ut) (b)) \ + : ((t) (((ut) (a) op (ut) (b)) - (tmin)) + (tmin))) + #endif /* _GL_INTPROPS_H */ |