RC4_CHAR is a bit in the x86(-64) CPUID information that switches the
RC4 asm code from using an array of 256 uint32_t's to 256 uint8_t's. It
was originally written for the P4, where the uint8_t style was faster.
(On modern chips, setting RC4_CHAR took RC4-MD5 from 458 to 304 MB/s.
Although I wonder whether, on a server with many connections, using less
cache wouldn't be better.)
However, I'm not too worried about a slowdown of RC4 on P4 systems these
days (the last new P4 chip was released nine years ago) and I want the
code to be simplier.
Also, RC4_CHAR was set when the CPUID family was 15, but Intel actually
lists 15 as a special code meaning "also check the extended family
bits", which the asm didn't do.
The RC4_CHAR support remains in the RC4 asm code to avoid drift with
upstream.
Change-Id: If3febc925a83a76f453b9e9f8de5ee43759927c6
Reviewed-on: https://boringssl-review.googlesource.com/3550
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
04c36b5062