Fwd: [PATCH] Fix remainder calculating bug in single floating point division

[Kumar Gala]

Begin forwarded message:

> From: Liu Yu <Yu.Liu@freescale.com>
> Date: January 6, 2008 8:26:53 AM CST
> To: linuxppc-dev@ozlabs.org
> Cc: Liu Yu <Yu.Liu@freescale.com>
> Subject: [PATCH] Fix remainder calculating bug in single floating  
> point division
>
> This bug exists in the emulation of floating point division for  
> powerpc.
>
> The original code cannot count the remainder correctly.
> I can provide a test case to trigger this bug.
> When use fdiv to count 1.1754941e-38f / 0.9999999f,
> the result is expected to be 1.175494e-38f,
> but we will get 1.174921e-38f in the original case.
>
> Comments are always welcomed!
>
> Signed-off-by: Liu Yu <Yu.Liu@freescale.com>
> ---
> arch/powerpc/math-emu/sfp-machine.h |   11 +++++------
> 1 files changed, 5 insertions(+), 6 deletions(-)

Since the math-emu support for PPC is based on some ancient version of  
the glibc/gcc soft-fp code I was wondering if anyone could look at  
Liu's issue and possibly comment if it exists elsewhere or if this is  
the correct fix for the issue.

thanks

- k

> diff --git a/arch/powerpc/math-emu/sfp-machine.h b/arch/powerpc/math- 
> emu/sfp-machine.h
> index 4b17d83..644cee2 100644
> --- a/arch/powerpc/math-emu/sfp-machine.h
> +++ b/arch/powerpc/math-emu/sfp-machine.h
> @@ -324,10 +324,10 @@ extern int  fp_pack_ds(void *, long, unsigned  
> long, unsigned long, long, long);
>     __r1 = __r1 * __ll_B | __ll_highpart (n0);				\
>     if (__r1 < __m)							\
>       {									\
> -	__q1--, __r1 += (d);						\
> -	if (__r1 >= (d)) /* we didn't get carry when adding to __r1 */	\
> -	  if (__r1 < __m)						\
> +	do {								\
> 	    __q1--, __r1 += (d);					\
> +	  /* we didn't get carry when adding to __r1 */			\
> +	} while (__r1 >= (d) && __r1 < __m);				\
>       }									\
>     __r1 -= __m;							\
> 									\
> @@ -337,10 +337,9 @@ extern int  fp_pack_ds(void *, long, unsigned  
> long, unsigned long, long, long);
>     __r0 = __r0 * __ll_B | __ll_lowpart (n0);				\
>     if (__r0 < __m)							\
>       {									\
> -	__q0--, __r0 += (d);						\
> -	if (__r0 >= (d))						\
> -	  if (__r0 < __m)						\
> +	do {								\
> 	    __q0--, __r0 += (d);					\
> +	} while (__r0 >= (d) && __r0 < __m);				\
>       }									\
>     __r0 -= __m;							\
> 									\
> -- 
> 1.5.2
>
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