Re: [PATCH] Fix carry bug in 128-bit unsigned integer adding
On Jan 8, 2008, at 9:05 PM, Liu Yu wrote: take a look at how include/math-emu/op-4.h implements __FP_FRAC_ADD_4 __FP_FRAC_SUB_4. Will that fix the bug, if so we should make the code match how its done there. - k The macro define __FP_FRAC_ADD_4 is below. It can fix the carry bug. But still exist a problem that r[0-2] and x[0-2] cannot be referred to the same variable. If r0 and x0 are the same variable, the comparison ( r0 x0 ) will always fail. I don't know whether we need to fix this problem. Not sure. Probably worth asking this on the glibc list and see if they have theories. (For the short term I'd say lets use the version from include/math-emu/op-4.h as a fix. If r0 x0 can be the same variable the bug exists in a lot more places (glibc soft-fp and generic kernel mathemu) - k ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: [PATCH] Fix carry bug in 128-bit unsigned integer adding
On Jan 6, 2008, at 8:26 AM, Liu Yu wrote: This bug exists in math emulation for powerpc. The macro define are mainly used by multiplication. When adding two unsigned operands ( r = x + y ), the carry bit can be counted by whether r is less than x. However, when adding three unsigned operands, this method does not work. The original code below uses this method to count carry, it apparently overlook the case of three operands. Assume all the operands is 32-bit wide, ( r = x + y + last_carry , x = 0, y = 0x, last_carry = 1), then r is no less than x but it actually gets a carry. I tried to fix this bug, but this patch seems not that pretty. Are there any better ideas? Comments are always welcomed! take a look at how include/math-emu/op-4.h implements __FP_FRAC_ADD_4 __FP_FRAC_SUB_4. Will that fix the bug, if so we should make the code match how its done there. - k ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
[PATCH] Fix carry bug in 128-bit unsigned integer adding
This bug exists in math emulation for powerpc.
The macro define are mainly used by multiplication.
When adding two unsigned operands ( r = x + y ),
the carry bit can be counted by whether r is less than x.
However, when adding three unsigned operands, this method does not work.
The original code below uses this method to count carry,
it apparently overlook the case of three operands.
Assume all the operands is 32-bit wide,
( r = x + y + last_carry , x = 0, y = 0x, last_carry = 1),
then r is no less than x but it actually gets a carry.
I tried to fix this bug, but this patch seems not that pretty.
Are there any better ideas?
Comments are always welcomed!
Signed-off-by: Liu Yu [EMAIL PROTECTED]
---
arch/powerpc/math-emu/op-4.h | 22 ++
1 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/math-emu/op-4.h b/arch/powerpc/math-emu/op-4.h
index fcdd6d0..93c7390 100644
--- a/arch/powerpc/math-emu/op-4.h
+++ b/arch/powerpc/math-emu/op-4.h
@@ -195,18 +195,24 @@
#ifndef __FP_FRAC_ADD_4
#define __FP_FRAC_ADD_4(r3,r2,r1,r0,x3,x2,x1,x0,y3,y2,y1,y0) \
- (r0 = x0 + y0, \
- r1 = x1 + y1 + (r0 x0), \
- r2 = x2 + y2 + (r1 x1), \
- r3 = x3 + y3 + (r2 x2))
+ do {
\
+ _FP_W_TYPE _x0 = x0, _x1 = x1, _x2 = x2, _y1 = y1, _y2 = y2;\
+ r0 = x0 + y0; \
+ r1 = x1 + y1 + (r0 _x0); \
+ r2 = x2 + y2 + (r1 _x1 || (r1 == _x1 !(_y1 + 1))); \
+ r3 = x3 + y3 + (r2 _x2 || (r2 == _x2 !(_y2 + 1))); \
+ } while(0)
#endif
#ifndef __FP_FRAC_SUB_4
#define __FP_FRAC_SUB_4(r3,r2,r1,r0,x3,x2,x1,x0,y3,y2,y1,y0) \
- (r0 = x0 - y0,\
- r1 = x1 - y1 - (r0 x0),\
- r2 = x2 - y2 - (r1 x1),\
- r3 = x3 - y3 - (r2 x2))
+ do {
\
+ _FP_W_TYPE _x0 = x0, _x1 = x1, _x2 = x2, _y1 = y1, _y2 = y2;\
+ r0 = x0 - y0; \
+ r1 = x1 - y1 - (r0 _x0); \
+ r2 = x2 - y2 - (r1 _x1 || (r1 == _x1 !(_y1 + 1))); \
+ r3 = x3 - y3 - (r2 _x2 || (r2 == _x2 !(_y2 + 1))); \
+ } while(0)
#endif
#ifndef __FP_FRAC_ADDI_4
--
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