#include <os/overflow.h>

os/overflow.h

Facilities for performing type- and overflow-checked arithmetic. These functions return non-zero if overflow occured, zero otherwise. In either case, the potentially overflowing operation is fully performed, mod the size of the output type. See: http://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins for full details. The compiler enforces that users of os_*_overflow() check the return value to determine whether overflow occured.

includes: sys/cdefs.h, stdbool.h, os/base.h

11 macros · 1 function

function__os_warn_unused

bool __header_always_inline OS_WARN_RESULT __os_warn_unused(__const bool x)

▾

claude-fable-5, 2026-08-24 · not from Apple sources · verified against xnu libkern/os/overflow.h

Identity function returning its boolean argument, marked OS_WARN_RESULT. The os_add_overflow, os_sub_overflow, os_mul_overflow, and related macros wrap their overflow-flag result in it so the compiler warns if a caller discards the overflow indication.

macroos_add_overflow

#define os_add_overflow(a, b, res) __os_warn_unused(__builtin_add_overflow((a), (b), (res)))

macroos_sub_overflow

#define os_sub_overflow(a, b, res) __os_warn_unused(__builtin_sub_overflow((a), (b), (res)))

macroos_mul_overflow

#define os_mul_overflow(a, b, res) __os_warn_unused(__builtin_mul_overflow((a), (b), (res)))

macroos_add3_overflow

os_add3_overflow(a, b, c) -> (a + b + c)

#define os_add3_overflow(a, b, c, res) __os_warn_unused(__extension__({
	__typeof(*(res)) _tmp;
	bool _s, _t;
	_s = os_add_overflow((a), (b), &_tmp);
	_t = os_add_overflow((c), _tmp, (res));
	_s | _t;
}))

macroos_sub3_overflow

os_sub3_overflow(a, b, c) -> ((a - b) - c)

#define os_sub3_overflow(a, b, c, res) __os_warn_unused(__extension__({
	__typeof(*(res)) _tmp;
	bool _s, _t;
	_s = os_sub_overflow((a), (b), &_tmp);
	_t = os_sub_overflow(_tmp, (c), (res));
	_s | _t;
}))

macroos_mul3_overflow

os_mul3_overflow(a, b, c) -> (a * b * c)

#define os_mul3_overflow(a, b, c, res) __os_warn_unused(__extension__({
	__typeof(*(res)) _tmp;
	bool _s, _t;
	_s = os_mul_overflow((a), (b), &_tmp);
	_t = os_mul_overflow((c), _tmp, (res));
	_s | _t;
}))

macroos_add_and_mul_overflow

os_add_and_mul_overflow(a, b, x) -> (a + b)*x

#define os_add_and_mul_overflow(a, b, x, res) __os_warn_unused(__extension__({
	__typeof(*(res)) _tmp;
	bool _s, _t;
	_s = os_add_overflow((a), (b), &_tmp);
	_t = os_mul_overflow((x), _tmp, (res));
	_s | _t;
}))

macroos_mul_and_add_overflow

os_mul_and_add_overflow(a, x, b) -> a*x + b

#define os_mul_and_add_overflow(a, x, b, res) __os_warn_unused(__extension__({
	__typeof(*(res)) _tmp;
	bool _s, _t;
	_s = os_mul_overflow((a), (x), &_tmp);
	_t = os_add_overflow((b), _tmp, (res));
	_s | _t;
}))

macroos_convert_overflow

os_convert_overflow(a) -> a [converted to the result type]

#define os_convert_overflow(a, res) os_add_overflow((a), 0, (res))

macroos_inc_overflow

os_inc_overflow(res) -> *res += 1

#define os_inc_overflow(res) __os_warn_unused(__extension__({
	__typeof((res)) _tmp = (res);
	os_add_overflow(*_tmp, 1, _tmp);
}))

macroos_dec_overflow

os_dec_overflow(res) -> *res -= 1

#define os_dec_overflow(res) __os_warn_unused(__extension__({
	__typeof((res)) _tmp = (res);
	os_sub_overflow(*_tmp, 1, _tmp);
}))