include: Implement N2867.

This adds macros for checked addition, subtraction, and multiplication with semantics similar to the builtins gcc and clang have had for years.

Reviewed by:	kib, emaste
Differential Revision:	https://reviews.freebsd.org/D41734

include/Makefile

@@ -30,7 +30,7 @@ INCS=	a.out.h ar.h assert.h bitstring.h byteswap.h \
 	pthread_np.h pwd.h ranlib.h readpassphrase.h regex.h \
 	res_update.h resolv.h runetype.h sched.h \
 	search.h semaphore.h setjmp.h \
-	signal.h spawn.h stab.h stdalign.h stdbool.h stddef.h \
+	signal.h spawn.h stab.h stdalign.h stdbool.h stdckdint.h stddef.h \
 	stdnoreturn.h stdio.h stdlib.h string.h stringlist.h \
 	strings.h sysexits.h tar.h termios.h tgmath.h \
 	time.h timeconv.h timers.h ttyent.h \

include/stdckdint.h

@@ -0,0 +1,40 @@
+/*-
+ * Copyright (c) 2023 Dag-Erling Smørgrav
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#ifndef __STDC_VERSION_STDCKDINT_H__
+#define __STDC_VERSION_STDCKDINT_H__ 202311L
+
+#include <sys/cdefs.h>
+
+#if __BSD_VISIBLE || __ISO_C_VISIBLE >= 2023
+
+#if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_add_overflow)
+#define ckd_add(result, a, b)						\
+	(_Bool)__builtin_add_overflow((a), (b), (result))
+#else
+#define ckd_add(result, a, b)						\
+	_Static_assert(0, "checked addition not supported")
+#endif
+
+#if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_sub_overflow)
+#define ckd_sub(result, a, b)						\
+	(_Bool)__builtin_sub_overflow((a), (b), (result))
+#else
+#define ckd_sub(result, a, b)						\
+	_Static_assert(0, "checked subtraction not supported")
+#endif
+
+#if __GNUC_PREREQ__(5, 1) || __has_builtin(__builtin_mul_overflow)
+#define ckd_mul(result, a, b)						\
+	(_Bool)__builtin_mul_overflow((a), (b), (result))
+#else
+#define ckd_mul(result, a, b)						\
+	_Static_assert(0, "checked multiplication not supported")
+#endif
+
+#endif
+
+#endif

share/man/man3/Makefile

@@ -29,6 +29,7 @@ MAN=		arb.3 \
 		snl.3 \
 		stats.3 \
 		stdarg.3 \
+		stdckdint.3 \
 		sysexits.3 \
 		tgmath.3 \
 		timeradd.3 \
@@ -310,6 +311,9 @@ MLINKS+=	stdarg.3 va_arg.3 \
 		stdarg.3 va_end.3 \
 		stdarg.3 varargs.3 \
 		stdarg.3 va_start.3
+MLINKS+=	stdckdint.3 ckd_add.3 \
+		stdckdint.3 ckd_sub.3 \
+		stdckdint.3 ckd_mul.3
 MLINKS+=	timeradd.3 timerclear.3 \
 		timeradd.3 timercmp.3 \
 		timeradd.3 timerisset.3 \

share/man/man3/stdckdint.3

@@ -0,0 +1,106 @@
+.\"-
+.\" Copyright (c) 2023 Dag-Erling Smørgrav
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.Dd September 5, 2023
+.Dt STDCKDINT 3
+.Os
+.Sh NAME
+.Nm stdckdint
+.Nd checked integer arithmetic
+.Sh SYNOPSIS
+.In stdckdint.h
+.Ft bool
+.Fn ckd_add "type1 *result" "type2 a" "type3 b"
+.Ft bool
+.Fn ckd_sub "type1 *result" "type2 a" "type3 b"
+.Ft bool
+.Fn ckd_mul "type1 *result" "type2 a" "type3 b"
+.Sh DESCRIPTION
+The function-like macros
+.Nm ckd_add ,
+.Nm ckd_sub ,
+and
+.Nm ckd_mul
+perform checked integer addition, subtraction, and multiplication,
+respectively.
+If the result of adding, subtracting, or multiplying
+.Fa a
+and
+.Fa b
+as if their respective types had infinite range fits in
+.Ft type1 ,
+it is stored in the location pointed to by
+.Fa result
+and the macro evaluates to
+.Dv false .
+Otherwise, the macro evaluates to
+.Dv true
+and the contents of the location pointed to by
+.Fa result
+is the result of the operation wrapped to the range of
+.Ft type1 .
+.Sh RETURN VALUES
+The
+.Nm ckd_add ,
+.Nm ckd_sub ,
+and
+.Nm ckd_mul
+macros evaluate to
+.Dv true
+if the requested operation overflowed the result type and
+.Dv false
+otherwise.
+.Sh EXAMPLES
+.Bd -literal -offset indent
+#include <assert.h>
+#include <limits.h>
+#include <stdckdint.h>
+
+int main(void)
+{
+	int result;
+
+	assert(!ckd_add(&result, INT_MAX, 0));
+	assert(result == INT_MAX);
+	assert(ckd_add(&result, INT_MAX, 1));
+	assert(result == INT_MIN);
+
+	assert(!ckd_sub(&result, INT_MIN, 0));
+	assert(result == INT_MIN);
+	assert(ckd_sub(&result, INT_MIN, 1));
+	assert(result == INT_MAX);
+
+	assert(!ckd_mul(&result, INT_MAX / 2, 2));
+	assert(result == INT_MAX - 1);
+	assert(ckd_mul(&result, INT_MAX / 2 + 1, 2));
+	assert(result == INT_MIN);
+
+	return 0;
+}
+.Ed
+.\" .Sh STANDARDS
+.\" The
+.\" .Nm ckd_add ,
+.\" .Nm ckd_sub ,
+.\" and
+.\" .Nm ckd_mul
+.\" macros conform to
+.\" .St -isoC-23 .
+.Sh HISTORY
+The
+.Nm ckd_add ,
+.Nm ckd_sub ,
+and
+.Nm ckd_mul
+macros were first introduced in
+.Fx 14.0 .
+.Sh AUTHORS
+The
+.Nm ckd_add ,
+.Nm ckd_sub ,
+and
+.Nm ckd_mul
+macros and this manual page were written by
+.An Dag-Erling Sm\(/orgrav Aq Mt [email protected] .