Demo code at http://svn.clifford.at/handicraft/2020/lut4perm/ …
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It looks like we are going to add a lut4 instruction to RISC-V BitManip (it's being moved from the crypto extension to bitmanip because it has many uses outside of crypto). Here's a little demo I wrote for it. Arbitrary 64-bit bit permutation in 15 instructions.pic.twitter.com/3n7TLLXdpU
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N00b question: what does lut4 mean?
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4-bit lookup table. The nibbles in the 2nd argument each select a nibble in the first argument. Use for 4-bit S-boxes with data in 2nd arg and table in 1st arg. Use for nibble permutation with data in 1st arg and permutation in 2nd arg.
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Looking forward to hardware-accelerated post-synth simulation with cxxrtl :D
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Look at that gorc go!
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I use it all the time now.
Here is my current version of a constant-time 8x8 sbox using lut4, also making good use of gorc.pic.twitter.com/wMpvYa6TTl
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Hmm..so how many RISC-V CPUs would I need to implement SERV?
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Maybe a really interesting thing would be to do software emulation much faster than Verilator.
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Will there be a yosys backend for riscv intrinsics?
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i've read the bitmanip draft a few times and a lot of the instructions are pretty hard to grok hopefully compilers do a better job than me :P
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