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A comment on Writing x86 SIMD using x86inc.asm (2017). Parent comment

Re:Writing x86 SIMD using x86inc.asm (2017) by astrange on Tuesday March 26, 2024 @09:48PM (#39834906)
The C version is in C because it needs to be portable and so there can be a baseline to find bugs in the other implementations.

The other ones aren't in asm merely because video codecs are "performance sensitive", it's because they're run in such specific contexts that optimizations work that can't be expressed portably in C+intrinsics across the supported compilers and OSes.

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Re:Writing x86 SIMD using x86inc.asm (2017) by Const-me on Wednesday March 27, 2024 @09:36AM (#39838881)
Yeah, it’s clear why you can’t have a single optimized C version.

However, can’t you have 5 different non-portable optimized C versions, just like you do with the assembly code?

SIMD intrinsics are generally portable across compilers and OSes, because their C API is defined by Intel, not by compiler or OS vendors. When I want software optimized for multiple targets like SSE, AVX1, AVX2, I sometimes do that in C++.

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