This is a discussion on Re: 0.9.8: cfb_enc.c bug? and AES speed on Win64/x64 - Openssl ; > | Some OpenSSL-algorithms are slower on x64, like RSA. SHA1 and RC4 seem to > | be faster [...] > > You said that RSA is slower on AMD64 ? This is not what he said. The claim was ...
> | Some OpenSSL-algorithms are slower on x64, like RSA. SHA1 and RC4 seem to
> | be faster [...]
> You said that RSA is slower on AMD64 ?
This is not what he said. The claim was that RSA is slower on *EM64T*
core and Win64 and this is not surprising. First of all note that 64-bit
C implementation goes with 4x32x32-bit multiplication to produce 128-bit
result. This is exactly as much as 32-bit assembler spends to produce as
much resulting bits. Now, benchmarks show that even if you deploy
64x64-bit multiplication instruction [this is what happens on Linux
thanks to GCC inline assembler support, which is *not* case/option on
Win64!], it doesn't get any faster on *Intel core*, presumably because
64x64-bit multiplication is implemented with 4x32x32 multiplications in
> This is unmistakably wrong, or
> at least, something must have gone terribly wrong during your
> benchmark. RSA heavily benefits from 64-bit arithmetic and by
> consequent AMD64 has a clear advantage over i386 (it is usually up to
> 3x faster).
On AMD64 cores, yes, but not on EM64T, at least not on currently
available cores. A.
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