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   Jeremy Kun (j2kun@mathstodon.xyz)'s status on Sunday, 01-Dec-2024 14:56:11 JST Jeremy Kun

   TIL that modern CPUs have an $F_2$-polynomial multiplication intrinsic operation: https://en.wikipedia.org/wiki/CLMUL_instruction_set

   • alcinnz repeated this.
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     Per Vognsen (pervognsen@mastodon.social)'s status on Sunday, 01-Dec-2024 15:14:47 JST Per Vognsen

     in reply to

     @j2kun And here's a fun application to parsing quoted strings: https://github.com/simdjson/simdjson/blob/cab383e1de7385c6460b66e5fad25a116d750402/src/generic/stage1/json_string_scanner.h#L67

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     Per Vognsen (pervognsen@mastodon.social)'s status on Sunday, 01-Dec-2024 15:14:48 JST Per Vognsen

     in reply to

     @j2kun Yeah, it's surprisingly useful. Aside from the classic "algebraic" use cases, there are some often useful bit tricks like computing the running bit parity by carryless multiplying by all ones/-1.

     alcinnz repeated this.
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     Per Vognsen (pervognsen@mastodon.social)'s status on Sunday, 01-Dec-2024 15:14:48 JST Per Vognsen

     in reply to

     @j2kun For example, if you mark the start and end of a range with a 1 bit then the running parity is a mask vector to select the bits in those ranges. You can even use this for computing rasterization coverage masks for potentially overlapping polygons where overlaps are resolved with the "mod 2" rule.

     alcinnz repeated this.