Problem with egcs and denormalized constants?

Problem with egcs and denormalized constants?

[Kevin B. Hendricks]

Hi,

The LinuxPPC port of JDK 1.2 can't pass the Java Compatibility Kit runtime-vm
tests because of some sort of error which is related to having very small
de-nromalized float constants.

I don't know whether this is an egcs problem (it happens with both egcs 1.1.1
and egcs 1.0.2), glibc problem (tested with the very latest glibc 1.99 rpm from
Gary) but it is an error.  

Will someone please compile and try the follwoing very simple test program and
help me understand what is happening here.  Is this an egcs problem?

[root@kbhend fltbug]# cat t3.c
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>


float flMin (int i)
 {
   float fl;
   if (i == 0) fl = 1.4023984e-37F;
   if (i == 1) fl = 1.4023984e-38F;
   if (i == 2) fl = 1.4023984e-39F;
   if (i == 3) fl = 1.4023984e-40F;
   if (i == 4) fl = 1.4023984e-41F;
   if (i == 5) fl = 1.4023984e-42F;
   if (i == 6) fl = 1.4023984e-43F;
   if (i == 7) fl = 1.4023984e-44F;
   if (i == 8) fl = 1.4023984e-45F;
   return fl;
 }


int main(int argc, char** argv)
{
  int i;
  float f;

  for (i=0;i<9;i++) {
     f = flMin(i);
     fprintf(stdout,"flmin(%1d) is %20.13e\n",i,f);
  }
  fprintf(stdout,"But flmin(7)/10.0F is %20.13e\n",(flMin(7)/10.0F));
}


Here is the output from my LinuxPPC box:

[root@kbhend fltbug]# ./t3
flmin(0) is  1.4023984275674e-37
flmin(1) is  1.4023983434895e-38
flmin(2) is  1.4023984836193e-39
flmin(3) is  1.4023914771270e-40
flmin(4) is  1.4024195030963e-41
flmin(5) is  1.4026997627891e-42
flmin(6) is  1.4012984643248e-43
flmin(7) is  1.4012984643248e-44
flmin(8) is  0.0000000000000e+00
But flmin(7)/10.0F is  1.4012984643248e-45            


Here is the correct output from my AIX box using an old version of gcc:

kbhend$ gcc -ot3 -O0 t3.c
kbhend$ ./t3
flmin(0) is  1.4023984275674e-37
flmin(1) is  1.4023983434895e-38
flmin(2) is  1.4023984836193e-39
flmin(3) is  1.4023914771270e-40
flmin(4) is  1.4024195030963e-41
flmin(5) is  1.4026997627891e-42
flmin(6) is  1.4012984643248e-43
flmin(7) is  1.4012984643248e-44
flmin(8) is  1.4012984643248e-45
But flmin(7)/10.0F is  1.4012984643248e-45


Notice the difference in the value of flmin(8) when loaded from a constant.

I looked at the assmebler and the constant for that value is correctly
identified and present.

What do you think?

Kevin

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RE: Problem with egcs and denormalized constants?

[Will Wood]

My LinuxPPC configuration is currently down but here's some results from
HP and Solaris.  All are
running EGCS-1.1.1

HPUX 10.20 EGCS 1.1.1 HP 9816

flmin(0) is  1.4023984275674e-37
flmin(1) is  1.4023983434895e-38
flmin(2) is  1.4023984836193e-39
flmin(3) is  1.4023914771270e-40
flmin(4) is  1.4024195030963e-41
flmin(5) is  1.4026997627891e-42
flmin(6) is  1.4012984643248e-43
flmin(7) is  1.4012984643248e-44
flmin(8) is  1.4012984643248e-45
But flmin(7)/10.0F is  1.4012984643248e-45

UltraSparc II/256 Solaris 2.6 EGCS-1.1.1

flmin(0) is  1.4023984275674e-37
flmin(1) is  1.4023983434895e-38
flmin(2) is  1.4023984836193e-39
flmin(3) is  1.4023914771270e-40
flmin(4) is  1.4024195030963e-41
flmin(5) is  1.4026997627891e-42
flmin(6) is  1.4012984643248e-43
flmin(7) is  1.4012984643248e-44
flmin(8) is  1.4012984643248e-45
But flmin(7)/10.0F is  1.4012984643248e-45

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Re: Problem with egcs and denormalized constants?

[Randy Gobbel]

"Kevin B. Hendricks" wrote:
> 
> Hi,
> 
> The LinuxPPC port of JDK 1.2 can't pass the Java Compatibility Kit runtime-vm
> tests because of some sort of error which is related to having very small
> de-nromalized float constants.
> 
> I don't know whether this is an egcs problem (it happens with both egcs 1.1.1
> and egcs 1.0.2), glibc problem (tested with the very latest glibc 1.99 rpm from
> Gary) but it is an error.
> 
> Will someone please compile and try the follwoing very simple test program and
> help me understand what is happening here.  Is this an egcs problem?
> 
> [root@kbhend fltbug]# cat t3.c
> #include <unistd.h>
> #include <stdlib.h>
> #include <string.h>
> #include <stdio.h>
> 
> float flMin (int i)
>  {
>    float fl;
>    if (i == 0) fl = 1.4023984e-37F;
>    if (i == 1) fl = 1.4023984e-38F;
>    if (i == 2) fl = 1.4023984e-39F;
>    if (i == 3) fl = 1.4023984e-40F;
>    if (i == 4) fl = 1.4023984e-41F;
>    if (i == 5) fl = 1.4023984e-42F;
>    if (i == 6) fl = 1.4023984e-43F;
>    if (i == 7) fl = 1.4023984e-44F;
>    if (i == 8) fl = 1.4023984e-45F;
>    return fl;
>  }
> 
> int main(int argc, char** argv)
> {
>   int i;
>   float f;
> 
>   for (i=0;i<9;i++) {
>      f = flMin(i);
>      fprintf(stdout,"flmin(%1d) is %20.13e\n",i,f);
>   }
>   fprintf(stdout,"But flmin(7)/10.0F is %20.13e\n",(flMin(7)/10.0F));
> }
> 
> Here is the output from my LinuxPPC box:
> 
> [root@kbhend fltbug]# ./t3
> flmin(0) is  1.4023984275674e-37
> flmin(1) is  1.4023983434895e-38
> flmin(2) is  1.4023984836193e-39
> flmin(3) is  1.4023914771270e-40
> flmin(4) is  1.4024195030963e-41
> flmin(5) is  1.4026997627891e-42
> flmin(6) is  1.4012984643248e-43
> flmin(7) is  1.4012984643248e-44
> flmin(8) is  0.0000000000000e+00
> But flmin(7)/10.0F is  1.4012984643248e-45
> 
> Here is the correct output from my AIX box using an old version of gcc:
> 
> kbhend$ gcc -ot3 -O0 t3.c
> kbhend$ ./t3
> flmin(0) is  1.4023984275674e-37
> flmin(1) is  1.4023983434895e-38
> flmin(2) is  1.4023984836193e-39
> flmin(3) is  1.4023914771270e-40
> flmin(4) is  1.4024195030963e-41
> flmin(5) is  1.4026997627891e-42
> flmin(6) is  1.4012984643248e-43
> flmin(7) is  1.4012984643248e-44
> flmin(8) is  1.4012984643248e-45
> But flmin(7)/10.0F is  1.4012984643248e-45
> 
> Notice the difference in the value of flmin(8) when loaded from a constant.
> 
> I looked at the assmebler and the constant for that value is correctly
> identified and present.
> 
> What do you think?

It's pretty easy to see what's going on if you look at it with gdb.  

(gdb) x/10 0x1802078
0x1802078 <.LC0>:       1.40239843e-37  1.40239834e-38  1.40239848e-39 
1.40239148e-40
0x1802088 <.LC4>:       1.4024195e-41   1.40269976e-42  1.40129846e-43 
1.40129846e-44
0x1802098 <.LC8>:       0       2.79124188e+23
(gdb) x/10x 0x1802078
0x1802078 <.LC0>:       0x023ee274      0x0098b529      0x000f4551     
0x000186ee
0x1802088 <.LC4>:       0x00002718      0x000003e9      0x00000064     
0x0000000a
0x1802098 <.LC8>:       0x00000000      0x666c6d69

Sure looks like an egcs bug to me.  The constant is being generated
incorrectly--it should show up as a 1 in hex.  If I manually stuff a 1
into .LC8, the program prints out the correct number:

(gdb) x/10x 0x1802078
0x1802078 <.LC0>:       0x023ee274      0x0098b529      0x000f4551     
0x000186ee
0x1802088 <.LC4>:       0x00002718      0x000003e9      0x00000064     
0x0000000a
0x1802098 <.LC8>:       0x00000001      0x666c6d69
(gdb) c
Continuing.
flmin(0) is  1.4023984275674e-37
flmin(1) is  1.4023983434895e-38
flmin(2) is  1.4023984836193e-39
flmin(3) is  1.4023914771270e-40
flmin(4) is  1.4024195030963e-41
flmin(5) is  1.4026997627891e-42
flmin(6) is  1.4012984643248e-43
flmin(7) is  1.4012984643248e-44
flmin(8) is  1.4012984643248e-45
But flmin(7)/10.0F is  1.4012984643248e-45

-Randy
--
http://www.cnbc.cmu.edu/~gobbel/
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Re: Problem with egcs and denormalized constants?

[Randy Gobbel]

P.S.: I just said the flMin problem was an egcs bug.  It's actually an
asm bug, because the constant is correct in the .s file:

.LC8:
	.float 0d1.40129846432481707092e-45

-Randy
-- 
http://www.cnbc.cmu.edu/~gobbel/
PGP fingerprint: 32 8A E8 24 A1 46 26 BC  F9 9D 0E B6 81 A9 02 0C

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Re: Problem with egcs and denormalized constants?

[David Edelsohn]

>>>>> Randy Gobbel writes:

Randy> P.S.: I just said the flMin problem was an egcs bug.  It's actually an
Randy> asm bug, because the constant is correct in the .s file:

Randy> .LC8:
Randy> .float 0d1.40129846432481707092e-45

	If I understand correctly, the bug actually is in glibc.  I
presume that the GNU assembler is not receiving the correct value when it
calls upon glibc to parse the constant for it to emit into the object
file.

David

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Re: Problem with egcs and denormalized constants?

[Randy Gobbel]

David Edelsohn wrote:
> 
> >>>>> Randy Gobbel writes:
> 
> Randy> P.S.: I just said the flMin problem was an egcs bug.  It's actually an
> Randy> asm bug, because the constant is correct in the .s file:
> 
> Randy> .LC8:
> Randy> .float 0d1.40129846432481707092e-45
> 
>         If I understand correctly, the bug actually is in glibc.  I
> presume that the GNU assembler is not receiving the correct value when it
> calls upon glibc to parse the constant for it to emit into the object
> file.

I've been poking around in binutils a bit, and it looks to me like the
badness is actually in gas.  Somewhere in expr.c is my current best
guess.  As far as I can tell, gas doesn't actually call glibc to
translate numbers, it has its own hairy platform-independent stuff for
that.

-Randy
-- 
http://www.cnbc.cmu.edu/~gobbel/
PGP fingerprint: 32 8A E8 24 A1 46 26 BC  F9 9D 0E B6 81 A9 02 0C

NOTICE: I DO NOT ACCEPT UNSOLICITED COMMERCIAL EMAIL MESSAGES OF ANY
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Re: Problem with egcs and denormalized constants?

[David Edelsohn]

>>>>> Randy Gobbel writes:

Randy> I've been poking around in binutils a bit, and it looks to me like the
Randy> badness is actually in gas.  Somewhere in expr.c is my current best
Randy> guess.  As far as I can tell, gas doesn't actually call glibc to
Randy> translate numbers, it has its own hairy platform-independent stuff for
Randy> that.

	Has anyone created a small, self-contained testcase and reported
it as a bug to binutils?

David

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Re: Problem with egcs and denormalized constants?

[Gary Thomas]

On 05-Mar-99 David Edelsohn wrote:
> 
>>>>>> Randy Gobbel writes:
> 
> Randy> I've been poking around in binutils a bit, and it looks to me like the
> Randy> badness is actually in gas.  Somewhere in expr.c is my current best
> Randy> guess.  As far as I can tell, gas doesn't actually call glibc to
> Randy> translate numbers, it has its own hairy platform-independent stuff for
> Randy> that.
> 
>       Has anyone created a small, self-contained testcase and reported
> it as a bug to binutils?
> 
> David
> 

I'm looking into it.  Note: it was only in the last few hours that this
problem with GAS/BINUTILS/??? became known.


------------------------------------------------------------------------
Gary Thomas                              |
email: gdt@linuxppc.org                  | "Fine wine is a necessity of
   ... opinions expressed here are mine  |        life for me"
       and no one else would claim them! |
                                         |      Thomas Jefferson
------------------------------------------------------------------------



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RE: Problem with egcs and denormalized constants?

[Gary Thomas]

This turns out to be a bug in the GAS IEEE FP code.  It could potentially
happen on any platform, but it is seldom seen from C code.  This is because
most of the GCC/EGCS back-ends generate raw hex values for the FP constants.
The PowerPC back-end uses the ".float" directive instead.

Anyway, I have a patch for GAS which fixes it.  I'll be making a new set of
binutils RPMS (rev 19b) which should be available later today at:
  ftp://ftp.linuxppc.org/linuxppc/users/gdt/redhat/RPMS/ppc/

On 04-Mar-99 Kevin B. Hendricks wrote:
> Hi,
> 
> The LinuxPPC port of JDK 1.2 can't pass the Java Compatibility Kit runtime-vm
> tests because of some sort of error which is related to having very small
> de-nromalized float constants.
> 
> I don't know whether this is an egcs problem (it happens with both egcs 1.1.1
> and egcs 1.0.2), glibc problem (tested with the very latest glibc 1.99 rpm from
> Gary) but it is an error.  
> 
> Will someone please compile and try the follwoing very simple test program and
> help me understand what is happening here.  Is this an egcs problem?
> 
> [root@kbhend fltbug]# cat t3.c
>#include <unistd.h>
>#include <stdlib.h>
>#include <string.h>
>#include <stdio.h>
> 
> 
> float flMin (int i)
>  {
>    float fl;
>    if (i == 0) fl = 1.4023984e-37F;
>    if (i == 1) fl = 1.4023984e-38F;
>    if (i == 2) fl = 1.4023984e-39F;
>    if (i == 3) fl = 1.4023984e-40F;
>    if (i == 4) fl = 1.4023984e-41F;
>    if (i == 5) fl = 1.4023984e-42F;
>    if (i == 6) fl = 1.4023984e-43F;
>    if (i == 7) fl = 1.4023984e-44F;
>    if (i == 8) fl = 1.4023984e-45F;
>    return fl;
>  }
> 
> 
> int main(int argc, char** argv)
> {
>   int i;
>   float f;
> 
>   for (i=0;i<9;i++) {
>      f = flMin(i);
>      fprintf(stdout,"flmin(%1d) is %20.13e\n",i,f);
>   }
>   fprintf(stdout,"But flmin(7)/10.0F is %20.13e\n",(flMin(7)/10.0F));
> }
> 
> 
> Here is the output from my LinuxPPC box:
> 
> [root@kbhend fltbug]# ./t3
> flmin(0) is  1.4023984275674e-37
> flmin(1) is  1.4023983434895e-38
> flmin(2) is  1.4023984836193e-39
> flmin(3) is  1.4023914771270e-40
> flmin(4) is  1.4024195030963e-41
> flmin(5) is  1.4026997627891e-42
> flmin(6) is  1.4012984643248e-43
> flmin(7) is  1.4012984643248e-44
> flmin(8) is  0.0000000000000e+00
> But flmin(7)/10.0F is  1.4012984643248e-45            
> 
> 
> Here is the correct output from my AIX box using an old version of gcc:
> 
> kbhend$ gcc -ot3 -O0 t3.c
> kbhend$ ./t3
> flmin(0) is  1.4023984275674e-37
> flmin(1) is  1.4023983434895e-38
> flmin(2) is  1.4023984836193e-39
> flmin(3) is  1.4023914771270e-40
> flmin(4) is  1.4024195030963e-41
> flmin(5) is  1.4026997627891e-42
> flmin(6) is  1.4012984643248e-43
> flmin(7) is  1.4012984643248e-44
> flmin(8) is  1.4012984643248e-45
> But flmin(7)/10.0F is  1.4012984643248e-45
> 
> 
> Notice the difference in the value of flmin(8) when loaded from a constant.
> 
> I looked at the assmebler and the constant for that value is correctly
> identified and present.
> 
> What do you think?
> 
> Kevin

------------------------------------------------------------------------
Gary Thomas                              |
email: gdt@linuxppc.org                  | "Fine wine is a necessity of
   ... opinions expressed here are mine  |        life for me"
       and no one else would claim them! |
                                         |      Thomas Jefferson
------------------------------------------------------------------------



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