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




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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