[PATCH] Fix bug on soft emulation of float point in gcc/longlong.c

[Liu Yu <Yu dot Liu at freescale dot com>]

There are 2 bugs existing in __udiv_qrnnd_c:

1. remainder could not be counted correctly
__r1 and __r0 are not adding enough, so I use do..while to replace former if

2. the case of overflow of __m are not considered
so I add a couple of lines to handle it

I found the bugs from Linux kernel,
for PowerPC math-emu use __udiv_qrnnd_c to emulate float div.

I sent the patch to the maintainers of kernel, but they replied to me that
this code came from gcc and should better keep coincident.
So I think I should send patch to here.

I don't know how to trigger __udiv_qrnnd_c in gcc.
but if the argument of __udiv_qrnnd_c are like
0x07fffff8 0x07fffff8 0x00210fff 0xc0000000 0x07fffff8,
the bug will be reproduced.

Also, you can try the program below, I have test it on Linux kernel math-emu but haven't test on gcc.

---
#include <stdio.h>

union fu {
	unsigned int u;
	float f;
};

union fu fdiv(union fu a, union fu b, union fu expected)
{
	union fu z;
	z.f = a.f / b.f;

	printf("fdiv %08x / %08x = %08x expected %08x %s\n",
			a.u, b.u, z.u, expected.u,
			(z.u == expected.u) ? "(PASS)" : "(FAIL)");
	printf("     %e / %e = %e\n", a.f, b.f, z.f);
}

int main()
{
	union fu fa,fb,fe;

	fa.u = 0xc0843fff;
	fb.u = 0x80ffffff;
	fe.u = 0x7f044000;
	fdiv(fa,fb,fe);
}

---


Signed-off-by: Liu Yu <Yu.Liu@freescale.com>
---
 gcc/longlong.h |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/gcc/longlong.h b/gcc/longlong.h
index 6c24564..256399b 100644
--- a/gcc/longlong.h
+++ b/gcc/longlong.h
@@ -1368,12 +1368,15 @@ UDItype __umulsidi3 (USItype, USItype);
     __q1 = (n1) / __d1;							\
     __m = (UWtype) __q1 * __d0;						\
     __r1 = __r1 * __ll_B | __ll_highpart (n0);				\
+    if (__d0 && __q1 > __m / __d0)					\
+	do {								\
+	    __q1--, __r1 += (d);					\
+	} while (__r1 >= (d));						\
     if (__r1 < __m)							\
       {									\
-	__q1--, __r1 += (d);						\
-	if (__r1 >= (d)) /* i.e. we didn't get carry when adding to __r1 */\
-	  if (__r1 < __m)						\
+	do {								\
 	    __q1--, __r1 += (d);					\
+	} while (__r1 >= (d) && __r1 < __m);				\
       }									\
     __r1 -= __m;							\
 									\
@@ -1381,12 +1384,15 @@ UDItype __umulsidi3 (USItype, USItype);
     __q0 = __r1 / __d1;							\
     __m = (UWtype) __q0 * __d0;						\
     __r0 = __r0 * __ll_B | __ll_lowpart (n0);				\
+    if (__d0 && __q0 > __m / __d0)					\
+	do {								\
+	    __q0--, __r0 += (d);					\
+	} while (__r0 >= (d));						\
     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