Why set zero in zero.c rather than use xor_n

[Torbjörn Granlund]

nisse at lysator.liu.se (Niels Möller) writes:

  It looks like internally we use the MPN_ZERO and MPN_FILL macros. The
  mpn_zero function is not inlined, as far as I see.
  
OK.

  > I am not sure it is important enough to write in asm, though.
  
  Probably not. But it might make sense to rewrite as a wrapper for
  memset, which I'd expect to be well optimized in gcc and libc.
  
I suppose memset is not used as it might come with more overhead for
checking alignment.  I haven't timed it, though.

(I checked the C version of memset in glibc.  Curiously, this is my old
code from 1991.  It uses a hardwired cutoff point of 8 bytes for
invoking non-trivial code.  That'd help.  Not sure if the asm code for
various CPUs do similarly.)

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Torbjörn
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