search for: rolx

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2018 Jul 02
2
Rotates, once again
...funnel shifts. I looked over some of the ISAs I have docs at hand for: - x86 (32b/64b variants) has SHRD/SHLD, so both right and left variants. Count is modulo (mod 32 for 32b instruction variants, mod 64 for 64b instruction variants). As of BMI2, we also get RORX (non-flag-setting ROR) but no ROLX. - ARM AArch64 has EXTR, which is a right funnel shift, but shift distances must be literal constants. EXTR with both source registers equal disassembles as ROR and is often special-cased in implementations. (EXTR with source 1 != source 2 often has an extra cycle of latency). There is RORV wh...
2018 Jul 02
2
Rotates, once again
1. I'm not sure what you mean by "full vector" here - using the same shift distance for all lanes (as opposed to per-lane distances), or doing a treat-the-vector-as-bag-of-bits shift that doesn't have any internal lane boundaries? If the latter, that doesn't really help you much with implementing a per-lane rotate. I think the most useful generalization of a vector