[LLVMdev] Floating point atomic load and add

[Tyler Denniston]

Got it. Thanks!

Quoting Tim Northover <t.p.northover at gmail.com>:

>> Hmm, ok. Can you briefly expand on how I should emulate this behavior? I
>> don't understand what you mean by adding a loop around cmpxchg.
>
> Probably easiest to write down in C:
>
> #include <stdatomic.h>
> void foo(_Atomic(float) *addr, float increment) {
>   float oldval = *addr, newval;
>   do {
>     newval = oldval + increment;
>   } while (__c11_atomic_compare_exchange_weak(
>       addr, &oldval, newval, memory_order_seq_cst, memory_order_relaxed));
> }
>
> Basically you keep trying to just swap in the new value until you've
> managed to do it atomically (or possibly with an intervening ABA
> change, but that doesn't matter usually).
>
> Tim.