4 ms·
rotate-and-xor (and xor-and-rotate) are both common operations in ARX ciphers. They demand 4 macro-ops in RISC-V, but only one in ARMv8. Bitfield insertion is
by brandmeyer 6y ago
rotate-and-xor (and xor-and-rotate) are both common operations in ARX ciphers. They demand 4 macro-ops in RISC-V, but only one in ARMv8.
Bitfield insertion is only one instruction in most RISC ISAs, but 5 or more in RISC-V.
- Veedrac 6y agoThe (unfinalized) bitmanip extension has single-op rotates.
- CalChris 6y agoI really don't like it. It seems like they copied x86 (bext, bdep) where they should have been plagiarizing armv8 (BFM, ...).
- brandmeyer 6y agoI've watched that extension's development since it was little more than one smart guy's wish list. I don't think its fair to say that they copied any one architecture. The authors have put in a ton of time researching the tradeoffs and investigating the trade space over the years. That said, until it gets ratified by the consortium and implemented in silicon its still just a (well-researched) wishlist.