Re: VAX sin/cos/atan2 vs polyd (Was: Does anyone have a netbsd-5 or earlier VAX to hand?)

[David Brownlee <abs%absd.org@localhost>]

Question first, rationale later :)

Question: Does anyone know of an VAX assembler implementation of
sin/cos and atan2 which avoids the use of POLY?

Rationale:

Thanks to those who ran the sintest program on their VAXen, it
looks like the issue was VAX CPU architecture specific rather than
OS revision (I knew POLY rang a bell somewhere :)

The POLY instruction was dropped in Rigel and later CPU variants,
which is a problem for NetBSD/vax's use of them in
lib/libm/arch/vax/{n_argred.S,n_atan2.S} - source at
http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libm/arch/vax/

There are a couple of obvious options to fix this:
a) Recode the assembly in those routines to avoid use of POLYD
b) Switch to a plain C implementation

(see question at top of email :)

Combined with a side option of:
 i) Doing one of the above unconditionally
ii) Having runtime logic to switch versions based on CPU implementation,
    potentially via an ld.so.conf extra library as used by i386 & sparc
    to conditionally load arch specific overlays

Assuming someone has an alternative implementation the side option
only becomes relevant if it is appreciably slower than the current
code on earlier VAX CPUs which implement POLY...