Re: Atomic floats on x86_64

[NightStrike <nightstrike@xxxxxxxxx>]

On Mon, Nov 10, 2014 at 3:58 AM, Andrew Haley <aph@xxxxxxxxxx> wrote:
> On 09/11/14 18:56, NightStrike wrote:
>> Is it a bug that I can atomically store a float using __atomic_store,
>> but not __atomic_store_n?  I'd really like to be able to do it without
>> the extra layer of indirection and the extra requirement of a temp
>> variable that I don't need.
>
> I don't get this.  Can you explain a bit more, or provide a test case?
> There shouldn't be any loss of performance.

For me, it's not a matter of performance (at least I hope, I didn't
measure).  It's more a matter of convenience.  I can't just atomically
stick a literal into a float.  I have to create temp variables
instead.

int main(void) {
    // Works fine:
    int a;
    __atomic_store_n(&a, 5, __ATOMIC_RELEASE);

    // Error: incompatible type for argument 1 of ‘__atomic_store_n’
    float b;
    __atomic_store_n(&b, 5.0f, __ATOMIC_RELEASE);

    // Works fine:
    float c = 5.0f;
    __atomic_store(&b, &c, __ATOMIC_RELEASE);

    return 0;
}