"Xvid is free software, and as such it can run on many
platforms: x86-32, x86-64, Power, ARM… And since assembly is
platform-specific, the Xvid developers decided to share as much
work as they could across those platforms: so, they used an
intermediary platform and language that could be matched to
assembly with minimal loss. This platform is NASM. In short,
whatever platform NASM supports, Xvid can run faster on. For all
the others, there is the plain C reference implementation.
"At the time of Xvid 1.1, NASM didn't support SSE2, much less 3,
and didn't support x86-64; so, for a while, Xvid on 64-bit AMD and
Intel systems made use of YASM, a mostly compatible implementation
of NASM that supported 64-bit. Since then though, NASM caught up
and Xvid dropped YASM support. Still, NASM's 64-bit support is very
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