Help. I cant find source for avr-libc function __divdi3

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N.Winterbottom
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Posted by N.Winterbottom: Mon. Feb 28, 2005 - 12:24 PM
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I tried doing a 64-Bit divide using long long variables, my hex file grew by about 5Kand no longer fits in my mega169, in my search to find out why, it looks as though __divdi3 is called.

I have a early copy of the avr-libc source (avr-libc-20011126) but CVS, particularly the SSH connection part of it is preventing me from obtaining an up to date copy.

Quote:
cvs -z3 -d:ext:anoncvs@savannah.gnu.org:/cvsroot/avr-libc co avr-libc
cvs [checkout aborted]: the :ext: access method is not installed on this system

Does anyone know which file contains commented source for the __divdi3 function?

Nigel

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Tools, Compilers and General Programming, ATmega16, ATmega169
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Bingo600
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Posted by Bingo600: Mon. Feb 28, 2005 - 01:07 PM
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Hi Nigel

Couldnt the "source" be helpfull :-)

I dont think there has been any major changes since 1.2.3 , and CVS chsckout might not be needed

Source
http://savannah.nongnu.org/downl...

PDF Manual
http://savannah.nongnu.org/downl...

/Bingo

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N.Winterbottom
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Posted by N.Winterbottom: Mon. Feb 28, 2005 - 02:32 PM
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Hi Bingo,

Tar very much. Ha Ha

That link was far easier than messing about with CVS.

Unfortunately I still cannot find any source references to divdi3 or indeed any other maths functions like udivmodsi4.

I might have to give up and decipher the raw LSS file instead.

Nigel

PS I don't understand your

Quote:
Couldnt the "source" be helpfull
comment ?

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EW
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Posted by EW: Mon. Feb 28, 2005 - 02:38 PM
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The divdi3 function actually comes from GCC. GCC has a small library, libgcc. For the avr it usually contains a bunch of low level math functions. So you'll have to go look at the GCC sources for this.

Eric Weddington
www.linkedin.com/in/ericweddington/

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Bingo600
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Posted by Bingo600: Mon. Feb 28, 2005 - 02:51 PM
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EW wrote:
The divdi3 function actually comes from GCC. GCC has a small library, libgcc. For the avr it usually contains a bunch of low level math functions. So you'll have to go look at the GCC sources for this.

Oopzzz

So we have a avr-libc , and a libgcc :oops: :oops:

Dammm , knew i should havent shipped reading the full "GCC Source" :? :?

Well thanx EW for saving me again :lol: :lol:

/Bingo

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N.Winterbottom
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Posted by N.Winterbottom: Mon. Feb 28, 2005 - 05:05 PM
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Well this has been a learning exercise !

I downloaded a snapshot "gcc-core-3.4-20050225.tar.bz2" from one of the few mirrors which actually responded in a timely manner.

In libgcc2.c I found:

#ifdef L_divdi3
DWtype
__divdi3 (DWtype u, DWtype v)
{
  word_type c = 0;
  DWunion uu = {.ll = u};
  DWunion vv = {.ll = v};
  DWtype w;

  if (uu.s.high < 0)
    c = ~c,
    uu.ll = -uu.ll;
  if (vv.s.high < 0)
    c = ~c,
    vv.ll = -vv.ll;

  w = __udivmoddi4 (uu.ll, vv.ll, (UDWtype *) 0);
  if (c)
    w = -w;

  return w;
}
#endif

This function is actually written in C. This goes some way to explain why my code grew so abominally. Some targets have this routine written in assembly using various methods but AVR doesn't so I'll have to "roll my own"

Nigel

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EW
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Posted by EW: Mon. Feb 28, 2005 - 06:34 PM
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If you want to be completely accurate you need to get the released version of gcc, version 3.4.3. What you have is a recent snapshot of the 3.4 branch, which is sometime after that release. Though I doubt that the code has actually changed for that function.

Eric Weddington
www.linkedin.com/in/ericweddington/

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dl8dtl
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Posted by dl8dtl: Mon. Feb 28, 2005 - 10:07 PM
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And of course, if you come up with an assembler implementation of it,
submit it to the GCC folks for inclusion.

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

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EW
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Posted by EW: Mon. Feb 28, 2005 - 11:05 PM
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And one way to do that is to compile it, then go and hand optimize the assembly. Be sure that it follows the AVR GCC ABI as listed in the avr-libc user manual (as a FAQ item).

Eric Weddington
www.linkedin.com/in/ericweddington/

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