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sse-alignment troubles

Obi Wan Kenobi · 2014-07-01T12:42:22

I got an array with input geometry, this is 100k entries array of triangles Triangle triangles[trianglesMAX]; each traingle is 9 floats (it is 36 bytes each) unfortunately this is not multiply of 16 bytes, and unfortunatelly to pad this up i need tu add whole 12 empty bytes so i wonder how i could change this, should i chnge the triangle for SseTriangle (or what better name for this) which is build from 12 floats (48 bytes) ? - it would grow input ram size from 3.6 MB to 4.8 MB this could slow the ram thing alternatively i could copy each record to local variable buffer and then work on this - not sure if this wouldnt be better (at all i got yet a little confusion here) other question is how 'keyword' in the GCC to use to align global and local storage variables for the usage of sse, i mean im mainly using the c types like float3 float9 float12 - how to align that? sse has some type called __m128 probably this is automaticaly aligned but it would be unconvinient to me to use this in all the places - in some sse agnostic places i would be liking using float3 then recast it to _m128 so i would prefer to use them both

General and Gameplay Programming Programming

Started by fir June 29, 2014 09:42 AM

32 comments, last by jbadams 9 years, 9 months ago

BitMaster

8,652

June 30, 2014 07:17 AM

Don't get me wrong I'm not defending/offending him, I just try to exchange useful information with all of you.
I think that if you put a downvote on someones post, you MUST tell him why he is wrong, at the end of the date we are programmers we use facts.

In an ideal world, yes. In practice, you need to check fir's history. The surprising thing is not he is getting downvoted without further comment, the surprising thing is there are people left who are actually willing to engage with him in something resembling a constructive way. Whatever else he is, he is very good at burning bridges for absolutely no reason at all.

fir

-460

Author

June 30, 2014 08:15 AM

Don't get me wrong I'm not defending/offending him, I just try to exchange useful information with all of you.
I think that if you put a downvote on someones post, you MUST tell him why he is wrong, at the end of the date we are programmers we use facts.

In an ideal world, yes. In practice, you need to check fir's history. The surprising thing is not he is getting downvoted without further comment, the surprising thing is there are people left who are actually willing to engage with him in something resembling a constructive way. Whatever else he is, he is very good at burning bridges for absolutely no reason at all.

this topic is about sse - i think you should answer to this not increase tons of blabla already present here,

Ohforf sake

2,052

June 30, 2014 09:48 PM

Sadly the other thread with the weird stack alignment bug got closed, so I can't post there anymore. But it seems like fir in his foresight created enough of them for everyone, so I'm just gonna post here.

For those of you, other then fir, who might have (or at some point in the future will) stumble across the same problem (aligned loads from the stack, generated by the compiler result in unaligned addresses) do not despair. There is another tool, next to the debugger, that fir also doesn't need, but that is very handy in this case, and which helped me a lot when I had to solve the very same problem (and I'm only sharing this, because it was a real WTF? moment for me). This tool is called google.

Just google for "GCC windows stack alignment" and pick (for example) the 3rd link that comes up, and you will get a nice explanation of the problem, alongside the solution.

Or, you can post a disassembly dump in the nearest internet community and wait for someone to figure it out, while you chill and play tetris *ducks and runs for the door*.