Found this [1], which also links to the Intel Optimization Manual [2]. Seems like ERMS was a cheaper replacement for AVX and FSRM was a better version, for sho

Found this [1], which also links to the Intel Optimization Manual [2]. Seems like ERMS was a cheaper replacement for AVX and FSRM was a better version, for shorter blocks. > Cheapest versions of later processors - Kaby Lake Celeron and Pentium, released in 2017, don't have AVX that could have been used for fast memory copy, but still have the Enhanced REP MOVSB. And some of Intel's mobile and low-power architectures released in 2018 and onwards, which were not based on SkyLake, copy about twice more bytes per CPU cycle with REP MOVSB than previous generations of microarchitectures. > Enhanced REP MOVSB (ERMSB) before the Ice Lake microarchitecture with Fast Short REP MOV (FSRM) was only faster than AVX copy or general-use register copy if the block size is at least 256 bytes. For the blocks below 64 bytes, it was much slower, because there is a high internal startup in ERMSB - about 35 cycles. The FSRM feature intended blocks before 128 bytes also be quick. [1] https://stackoverflow.com/a/43837564 https://stackoverflow.com/a/43837564 [2] http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf http://www.intel.com/content/dam/www/public/us/en/documents/...