cub, c.parallel: {lower,upper}_bound #7007
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shwina
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Dec 18, 2025
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| const unsigned int thread_count = 256; | ||
| const size_t items_per_block = 512; |
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Are these essentially hardcoded somewhere in the CUB as well?
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Yes. There's no tunings for for, and this just follows that.
I'm planning to start working on a warp level binary search algorithm in the new year, and then build a device wide one on top of that, as a replacement of the current approach - we'll do actual tunings then.
shwina
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Dec 19, 2025
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The C side looks good to me. Thanks!
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Description
This PR adds {lower,upper}_bound device algorithms to both CUB and c.parallel.
In the case of CUB, the implementation is very straightforward and directly follows current implementation in Thrust (which I have cleaned up as a drive by change).
In the case of c.parallel, because of how CUB's
for_eachpasses in kernel arguments, repeating the slight madness of the currentforoperator construction for the for_each algorithm itself felt beyond annoying, but I needed a kernel pointer; so instead of reusing the kernels available in CUB, I adapted the static-block-sizefor_eachkernel to accept all the necessary arguments as separate kernel arguments, then construct the for operator expected by CUB inside the kernel, and finally invoke the CUBfor_eachagent with that operator. So, it's a manually constructed kernel, but it reuses both the agent code and binary search helper types from CUB.Resolves #6695
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