[Bug target/39085] Floating point errors on Arm9 processor

2009-03-25 Thread rearnsha at gcc dot gnu dot org 


--- Comment #6 from rearnsha at gcc dot gnu dot org  2009-03-25 21:54 
---
(In reply to comment #2)
   str   r3, [fp, #-32]
   str   r4, [fp, #-28]
   ldfd  f0, [fp, #-32]
   sqtd  f0, f0
   stfd  f0, [fp, #-40]
   ldfd  f0, [fp, #-40]
   ldfd  f0, [fp, #-40]
   cmf   f0, f0
   beq   .L2
   sub   r0, fp, #32
   ldmia r0, {r0-r1}
   blsqrt
   stfd  f0, [fp, #-40]

You need to understand what this code is doing to work out the source of the
bug.  The compiler is inlining a copy of the square-root function with an FPA
co-processor instruction

sqtd  f0, f0

which, if successful will replace the library call.  If the square root
succeeds it will not return a NaN, so the comparison of the result

cmf   f0, f0

will be that the two results are equal (a NaN never compares equal to itself).

So the square root function (sqrt) will only be called if a NaN was generated
by the machine instruction; it does this in order to set errno.

Of course, the ARM9 does not have an FPA co-processor so the original sqtd
instruction will be emulated by your operating system -- I strongly suspect
that that is what is generating the incorrect results and you now need to
investigate why.

If you still believe the bug is in the compiler you need to provide some
additional information, including how you configured the compiler and what
options you used when compiling your code.


-- 

rearnsha at gcc dot gnu dot org changed:

   What|Removed |Added

 CC||rearnsha at gcc dot gnu dot
   ||org
 Status|WAITING |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085

[Bug target/39085] Floating point errors on Arm9 processor

2009-03-13 Thread mp2 at ladybridge dot com 


--- Comment #5 from mp2 at ladybridge dot com  2009-03-13 17:36 ---
Is there any progress on looking at this problem? It is causing a delay in
releasing software on the Arm9 processor.

Thanks.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085

[Bug target/39085] Floating point errors on Arm9 processor

2009-02-16 Thread mp2 at ladybridge dot com 


--- Comment #4 from mp2 at ladybridge dot com  2009-02-16 09:10 ---
(In reply to comment #3)
 I would generate the assembly by using a local function name rather than
 using main().
The original problem was deep in a complex program. I was trying to bring it
down to the shortest program that demonstrated the issue.

 From what I'm seeing, I don't know if it might be a typecasting issue
did you try something like this?  (float)out = sqrt((float)in); 

Tried this and it still fails.

Also, the problem affects many mathematical functions, not just sqrt(). I first
saw it with sin().

Thanks for your help.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085

[Bug target/39085] Floating point errors on Arm9 processor

2009-02-15 Thread mp2 at ladybridge dot com 


--- Comment #2 from mp2 at ladybridge dot com  2009-02-15 12:14 ---
(In reply to comment #1)
 sqrt is usually implemented as a library function and GCC does not implement 
 it
 for you.  Do you use newlib?

My previous reply doesn't seem to have made it into the system. Here it is
again...
As far as I can see, there is no library named newlib or anything near it on
this system. What is this library and where do I get it?

I am not convinced that this is a library issue as two of the sqrt() functions
in the program work though the last has been pre-evaluated to a constant by the
gcc compiler. The problem only happens when the result is stored in a variable.

I cannot find any good documentation for the Arm9 assembler but by inspired
guesswork interpreting the instruction names, the code generated for the
program looks very odd as there appears to be a conditional jump around the
sqrt() function.

int main()
{
 double in, out;
 in = 2.0;
 out = sqrt(in);
 printf(%f\n, out);
 printf(%f\n, sqrt(in));
 printf(%f\n, sqrt(2.0));
 return 0;
}

Assembler code...

  .file a.c
  .section  .rodata
  .align2
.LC0:
  .ascii%f\012\000
  .text
  .align2
  .global   main
  .type main, %function
main:
  @ args = 0, pretend = 0, frame = 24
  @ frame_needed = 1, uses_anonymous_args = 0
  mov   ip, sp
  stmfd sp!, {r4, fp, ip, lr, pc}
  sub   fp, ip, #4
  sub   sp, sp, #24
  adr   r3, .L4
  ldmia r3, {r3-r4}
  str   r3, [fp, #-32]
  str   r4, [fp, #-28]
  ldfd  f0, [fp, #-32]
  sqtd  f0, f0
  stfd  f0, [fp, #-40]
  ldfd  f0, [fp, #-40]
  ldfd  f0, [fp, #-40]
  cmf   f0, f0
  beq   .L2
  sub   r0, fp, #32
  ldmia r0, {r0-r1}
  blsqrt
  stfd  f0, [fp, #-40]
.L2:
  sub   r3, fp, #40
  ldmia r3, {r3-r4}
  str   r3, [fp, #-24]
  str   r4, [fp, #-20]
  ldr   r0, .L4+16
  sub   r1, fp, #24
  ldmia r1, {r1-r2}
  blprintf
  sub   r0, fp, #32
  ldmia r0, {r0-r1}
  blsqrt
  stfd  f0, [sp, #-8]!
  ldmfd sp!, {r3, r4}
  ldr   r0, .L4+16
  mov   r1, r3
  mov   r2, r4
  blprintf
  ldr   r0, .L4+16
  adr   r1, .L4+8
  ldmia r1, {r1-r2}
  blprintf
  mov   r3, #0
  mov   r0, r3
  sub   sp, fp, #16
  ldmfd sp, {r4, fp, sp, pc}
.L5:
  .align2
.L4:
  .word 1073741824
  .word 0
  .word 1073127582
  .word 1719614413
  .word .LC0
  .size main, .-main
  .identGCC: (GNU) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)


Martin Phillips
Ladybridge Systems Ltd
17b Coldstream Lane, Hardingstone, Northampton, NN4 6DB
+44-(0)1604-709200


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085

[Bug target/39085] Floating point errors on Arm9 processor

2009-02-15 Thread rbala at coresfoundation dot com 


--- Comment #3 from rbala at coresfoundation dot com  2009-02-15 20:43 
---
Hi all,

Correct me if I'm wrong.

@mp2 - newlib is a source of 'C' libraries for various arch's. You won't find a
directory as such called newlib. While building your toolchain, you compile all
the files in the newlib source.

Coming to your issue, I shall verify it again. I don't think it is a GCC
issue., but I shall verify it. I saw the assembly code, but I shall again
generate the assembly myself., atleast from my perspective, I would generate
the assembly by using a local function name rather than using main().
I mean I wouldn't use the fn.name as main() when I was to debug a function's
assembly, because main() being a generic fn. Name might induce some other
fn.calls(I may be wrong here) but what I'm saying is, its just a good practice.

From what I'm seeing, I don't know if it might be a typecasting issue, (don't
know for sure), did you try something like this?  (float)out =
sqrt((float)in); 
(In reply to comment #2)
 (In reply to comment #1)
  sqrt is usually implemented as a library function and GCC does not 
  implement it
  for you.  Do you use newlib?
 
 My previous reply doesn't seem to have made it into the system. Here it is
 again...
 As far as I can see, there is no library named newlib or anything near it on
 this system. What is this library and where do I get it?
 
 I am not convinced that this is a library issue as two of the sqrt() functions
 in the program work though the last has been pre-evaluated to a constant by 
 the
 gcc compiler. The problem only happens when the result is stored in a 
 variable.
 
 I cannot find any good documentation for the Arm9 assembler but by inspired
 guesswork interpreting the instruction names, the code generated for the
 program looks very odd as there appears to be a conditional jump around the
 sqrt() function.
 
 int main()
 {
  double in, out;
  in = 2.0;
  out = sqrt(in);
  printf(%f\n, out);
  printf(%f\n, sqrt(in));
  printf(%f\n, sqrt(2.0));
  return 0;
 }
 
 Assembler code...
 
   .file a.c
   .section  .rodata
   .align2
 .LC0:
   .ascii%f\012\000
   .text
   .align2
   .global   main
   .type main, %function
 main:
   @ args = 0, pretend = 0, frame = 24
   @ frame_needed = 1, uses_anonymous_args = 0
   mov   ip, sp
   stmfd sp!, {r4, fp, ip, lr, pc}
   sub   fp, ip, #4
   sub   sp, sp, #24
   adr   r3, .L4
   ldmia r3, {r3-r4}
   str   r3, [fp, #-32]
   str   r4, [fp, #-28]
   ldfd  f0, [fp, #-32]
   sqtd  f0, f0
   stfd  f0, [fp, #-40]
   ldfd  f0, [fp, #-40]
   ldfd  f0, [fp, #-40]
   cmf   f0, f0
   beq   .L2
   sub   r0, fp, #32
   ldmia r0, {r0-r1}
   blsqrt
   stfd  f0, [fp, #-40]
 .L2:
   sub   r3, fp, #40
   ldmia r3, {r3-r4}
   str   r3, [fp, #-24]
   str   r4, [fp, #-20]
   ldr   r0, .L4+16
   sub   r1, fp, #24
   ldmia r1, {r1-r2}
   blprintf
   sub   r0, fp, #32
   ldmia r0, {r0-r1}
   blsqrt
   stfd  f0, [sp, #-8]!
   ldmfd sp!, {r3, r4}
   ldr   r0, .L4+16
   mov   r1, r3
   mov   r2, r4
   blprintf
   ldr   r0, .L4+16
   adr   r1, .L4+8
   ldmia r1, {r1-r2}
   blprintf
   mov   r3, #0
   mov   r0, r3
   sub   sp, fp, #16
   ldmfd sp, {r4, fp, sp, pc}
 .L5:
   .align2
 .L4:
   .word 1073741824
   .word 0
   .word 1073127582
   .word 1719614413
   .word .LC0
   .size main, .-main
   .identGCC: (GNU) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
 
 
 Martin Phillips
 Ladybridge Systems Ltd
 17b Coldstream Lane, Hardingstone, Northampton, NN4 6DB
 +44-(0)1604-709200
 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085

[Bug target/39085] Floating point errors on Arm9 processor

2009-02-03 Thread pinskia at gcc dot gnu dot org 


--- Comment #1 from pinskia at gcc dot gnu dot org  2009-02-03 19:35 ---
sqrt is usually implemented as a library function and GCC does not implement it
for you.  Do you use newlib?


-- 

pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

   Severity|major   |normal
 Status|UNCONFIRMED |WAITING
  Component|c   |target


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39085