Summary: math/trig functions vs -f68881

[or uunet!sli!rdh]

I had asked how to get the C compiler to generate code to use the MC68881
trig functions . . .

OK, OK, it really was there in the manual (there's a big difference 'twixt
R'ing the FM, and U'ing the FM: I actually did see the section on inlining
[Floating Point Programmer's Guide: Appendix "G" -- Assembly- Level
In-line Expansion], but just glanced at it as a "interesting if somewhat
kinky way of implementing INLINE capability in a compiler for a language
that doesn't support INLINE as a language construct. After all, I just
wanted the compiler to use the MC68881 coprocessor, not write obtuse
machine code...and it wasn't anywhere near all the other stuff in the
manual on the MC68881 coprocessor and attendant switches...  [An appendix,
no less!]

Probably the most, ah, authoritative response:

  f68881 means use the MC6888x fp chip for ordinary fp arithmetic (add,
  subtract, multiply, divide, ...)

  To use the MC6888x chips' implementation of transcendental functions,
  compile like so:

	  cc -f68881 /usr/lib/f68881/libm.il myprog.c -lm

  The reason for this has to do with SVID compliance; in order to
  generate (the silly) MATHERR error notification, we can't use the
  MC6888x stuff directly, but instead need to go through software
  routines that can signal MATHERR.

  (If you use the inline templates, then in this minor way you lose SVID
  compliance.   I'm not sure why anyone cares about SVID compliance - we
  the implementors certainly don't - it must have something to do with
  the phone company.)

  The new unbundled compilers have a switch for the inline library
  templates (-libmil) and the FPPG was rewritten as the Numerical
  Computation Guide (part number 800-3555-10).  The NCG attempts to sketch
  how libm is implemented for the various fp architectures.

and, of course, the usual pitch for GNU/gcc:

  You can get inline trig code by compiling with the inline maths lib
  /usr/lib/f68881/libm.il in the command line.   It is better but not
  great.  A much beter alternative is to use gcc and the math-68881.h
  header that does all the inline trig stuff, and avoids all register
  spills etc at the same time.

Many MANY thanks to all who took the time and effort to respond:

  bobg at xn.ll.mit.edu
  uunet^icarus.eng.ohio-state.edu.eng.ohio-state.edu^kaul at sli (Rich Kaul)
  Brian Fitzgerald <uunet^mml0.meche.rpi.edu^fitz at sli>
  vanandel at ncar.ucar.edu
  Bruce Allen <uunet^csd4.csd.uwm.edu^ballen at sli>
  prl at iis.ethz.ch
  Skip (montanaro at crdgw1.ge.com)
  uunet^Eng.Sun.COM^khb at sli (chiba)
  mrm at eng.sun.com
  glenn at synaptics.com
  uunet^auspex.com^guy at sli (Guy Harris)
  Bill Dunlap <uunet^stat.washington.edu^bill at sli>
  jimc at math.ucla.edu
  uunet^Eng.Sun.COM^dgh at sli (David Hough)
  brent at dimsun.bcm.tmc.edu
  AKONSTAM at TRINITY.BITNET
  Gregory Bond <uunet^melba.bby.oz.au^gnb at sli>

and any others whose mail may have been foiled by the network mail munching
trolls...this group is *GREAT* !!
					-RDH