| > https://www.intel.com/content/www/us/en/docs/intrinsics-guid... Intel's Intrinsics Guide is exactly what I used and it was before I learned about Compiler Explorer. I already had a large and thorough suite of unit tests for inputs and expected outputs, including happy and sad paths. So it was pretty easy to poke around and learn what works, what doesn't. It was definitely time intensive (took about three months for about 50 lines of code) but it also saved the company a few million dollars in hardware (DNA analysis software to compare a couple TiB of data requires a _lot_ of performance). I have since moved to a different company, partly because I never saw a bonus for saving all that money. The intrinsics guide does good to show what's available but it does not do a good job of documenting how each instruction actually works... many intrinsics are missing pseudocode and some pseudocode can have ambiguous cases. I used GDB in assembly mode to compare that table against the register content instruction-by-instruction to figure out where I misunderstood something if something went awry. Frustratingly, some operations are available in 64-bits but not bigger, some in 128-bits but not bigger, etc. So I wrote up a rough draft in LibreOffice Calc with 64, 128, and 256 columns to follow the bits around every intended operation. I then correlated against the intrinsics guide to determine what instructions are available to me in what bit sizes. For a given test run, each row in the spreadsheet was colored by what the original data contained, another row for what I needed the answer to be for that test case, then auto-color another row's cell green or red if the register after a candidate set of instructions did or didn't match the desired output. Any time I had to move columns around (the data was 4-bits wide), I'd color a set of 4 columns to follow where they go during swizzling. |