Ping? Please take a look. Thanks. There was some related discussion about overflow builtins from GCC, FYI.
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48580
I also created a higher-level library on top of these builtins for
demonstration.
https://github.com/xiw/libo
Basically it provides the following functions (macros/wrappers).
bool overflow_add(type *, type, type);
bool overflow_sub(type *, type, type);
bool overflow_mul(type *, type, type);
bool overflow_div(type *, type, type);
You even can use them with GCC (or Clang without overflow builtins). Their
implementations (in assembly) are generated automatically via Clang, except for
overflow_div(), which doesn't depend on overflow builtins.
- xi
overflow.patch
Description: Binary data
On Apr 4, 2012, at 8:18 PM, Xi Wang wrote:
> Hi,
>
> Attached is a patch that adds arithmetic with overflow builtins to Clang.
> Please review. Thanks.
>
> Arithmetic with overflow builtins are used to perform arithmetic operations
> with overflow detection.
>
> Syntax:
>
> bool __builtin_add_with_overflow(type *ptr, type a, type b);
> bool __builtin_sub_with_overflow(type *ptr, type a, type b);
> bool __builtin_mul_with_overflow(type *ptr, type a, type b);
>
> Example of Use:
>
> void *malloc_array(size_t n, size_t size) {
> size_t bytes;
> if (__builtin_mul_with_overflow(&bytes, n, size))
> return NULL;
> return malloc(bytes);
> }
>
> Description:
>
> __builtin_op_with_overflow(ptr, a, b) stores the result of a op b in ptr, and
> returns true if an overflow occurred during the arithmetic operation. Note
> that type is inferred from *ptr. These builtins help developers write more
> efficient and correct code by avoiding ad hoc overflow checks.
>
> Query for this feature with __has_builtin(__builtin_op_with_overflow).
>
> - xi
> <overflow.patch>
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