C implementation of mod_1_1

Torbjorn Granlund tg at gmplib.org
Wed Mar 2 11:01:02 CET 2011

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

  Does the following look reasonable? It's based on some cargo-culting of
  the macros in longlong.h; I don't understand the subtleties with gcc
  inline asm and the various register attributes.
  #if defined (__sparc__) && W_TYPE_SIZE == 32
  #define add_mssaaaa(m, sh, sl, ah, al, bh, bl)				\
    __asm__ ("addcc %r5,%6,%2\n\taddxcc %r3,%4,%1\n\tsubx %%g0,%%g0,%0"	\
  	   : "=r" (m), "=r" (sh), "=&r" (sl)				\
  	   : "rJ" (ah), "rI" (bh),"%rJ" (al), "rI" (bl)			\

This looks OK.
  #if defined (__sparc__) && W_TYPE_SIZE == 64
  #define add_mssaaaa(m, sh, sl, ah, al, bh, bl)				\
    __asm__ (								\
         "addcc	%r4,%5,%1\n"						\
        "	addccc	%r6,%7,%%g0\n"						\
        "	addc	%r2,%3,%0\n"						\
        " addccc  %r8,%r9,%%g0\n"						\
        " subcc   %%g0,%%g0,%0"						\
  	  : "=r" (sh), "=&r" (sl)					\
  	  : "rJ" (ah), "rI" (bh), "%rJ" (al), "rI" (bl),		\
  	    "%rJ" ((al) >> 32), "rI" ((bl) >> 32),			\
  	    "%rJ" ((ah) >> 32), "rI" ((bh) >> 32),			\
Perhaps do some tab/space cleanup inside the asm string.
I'd sort the input operands so that high operands come first
cnsistently, i.e., swap the lines comtaining ' >> 32'.

  Is subcc %g0,%g0,m the best way to get the carry flag to a mask? Or can
  one use some other construction to make use the CCR.xcc bit? 

There is also a movcc, conditional move.  It can take xcc and icc as
input.  I don't recall if it takes immediate operands as input.

  The 64-bit attempt above uses an awful lot of registers, maybe I should
  look into the signbit logic (but I suspect it's a bit hairy to get right
  if you also have carry in)? If we get the carry result into the signbit
  position, we should get the mask easily using srax (arithmetic 64-bit
  right shift).
Or perhaps ignore sparc64 as too broken to be worth it...

  > Unfortunately, the venerable mc68040 system of the GMP test array has a
  > dead PSU.  I got it to boot with a lab PSU setup, but I have not found
  > the time to repair the PSU yet...  Some may argue that GMP for m68k is
  > not critically important.
  I don't know what applications current 68k processors (under the name
  "coldfire" if I have understood it correctly) are used for.
Embedded.  They lack GMP's avourite insn, 32x32->64 multiply, I think.

  One possibility is to install the aranym atari emulator and install
  debian's m68k port. I've heard that some of debian's m68k build machines
  are setup that way. Benchmark and tuning results might of course be of
  somewhat questionable value...

Yes, things would run too fast to be realistic.  :-)


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