InterlockedAdd on R32_Sint with negative number

user_3562271 0
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I am writing to an RWBuffer<int> using InterlockedAdd - originally I had an RWBuffer<uint> but I needed my values to go negative sometimes.

I find that using InterlockedAdd passing a negative number doesn't update the underlying int buffer - I tested this by using abs() on the value being passed in, and it worked.

I realize using an Add method to add a negative number might seem like "doh ! what did you expect" but there isnt an InterlockedSubtract() so ...

Is this a known issue that I just haven't managed to find the docs for, or would you normally expect InterlockedAdd(-1) to subtract 1 from an RWBuffer<int> like I did ?

hlsl directx-11
1 Answers

I'm not sure how atomics are handled with typed buffers, but they definitely work with structured buffers.

In your case since typed buffer is R32 it would perfectly map to a int structured buffer.

Syntax would be :

RWStructuredBuffer<int> OutputBuffer : register(u0);

Then interlocked operation would be like (if you want to apply it on the 2nd element for example):

uint idx = 1;
uint current_value;
InterlockedAdd(OutputBuffer[idx],-1,current_value);

Buffer creation is slightly different, but nothing too complicated as a change (need to set the structured flag and also set element stride, which is 4 in that case).

user_16412200
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