Date: Wed, 28 Mar 2012 12:30:46 GMT From: Ilya Burylov <ilya.burylov@gmail.com> To: freebsd-gnats-submit@FreeBSD.org Subject: standards/166463: remquo[f] may return wrong sign in quo part and incorrect rem part on denormals Message-ID: <201203281230.q2SCUk5q075041@red.freebsd.org> Resent-Message-ID: <201203281240.q2SCe9jT045209@freefall.freebsd.org>
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>Number: 166463
>Category: standards
>Synopsis: remquo[f] may return wrong sign in quo part and incorrect rem part on denormals
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-standards
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Mar 28 12:40:09 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator: Ilya Burylov
>Release: Found in Android Bionic
>Organization:
Intel
>Environment:
Found in Android Bionic
>Description:
Currently we will get the wrong result as follows:
remquof(0x7bb33336, 0x63000000) = -671088640, 0x00000000 /* wrong sign in quo */
remquo(0xbff0000000000003, 0x3ff0000000000003) = 1, 0x8000000000000000 /* wrong sign in quo */
remquo(0x9120000000000001, 0x0000000000000005) = -1288490188, 0x0000000000000004 /* wrong quo and rem parts */
while [an example of] correct one should be:
remquof(0x7bb33336, 0x63000000) = 1476395008, 0x00000000
remquo(0xbff0000000000003, 0x3ff0000000000003) = -1, 0x8000000000000000
remquo(0x9120000000000001, 0x0000000000000005) = -1288490189, 0x0000000000000001
That does not fit into description in C99 standard: e.g. "In
the object pointed to by quo they store a value whose sign is the sign of x/y"
Fix attached
>How-To-Repeat:
Reproducible in description
>Fix:
Fix should be applied to
\msun\src\s_remquo.c
\msun\src\s_remquof.c
Fix attached.
Patch attached with submission follows:
Index: src/s_remquof.c
===================================================================
--- src/s_remquof.c (revision 233542)
+++ src/s_remquof.c (working copy)
@@ -46,7 +46,7 @@
q = 0;
goto fixup; /* |x|<|y| return x or x-y */
} else if(hx==hy) {
- *quo = 1;
+ *quo = (sxy ? -1 : 1);
return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
}
@@ -88,6 +88,7 @@
/* convert back to floating value and restore the sign */
if(hx==0) { /* return sign(x)*0 */
+ q &= 0x7fffffff;
*quo = (sxy ? -q : q);
return Zero[(u_int32_t)sx>>31];
}
Index: src/s_remquo.c
===================================================================
--- src/s_remquo.c (revision 233542)
+++ src/s_remquo.c (working copy)
@@ -51,7 +51,7 @@
goto fixup; /* |x|<|y| return x or x-y */
}
if(lx==ly) {
- *quo = 1;
+ *quo = (sxy ? -1 : 1);
return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
}
}
@@ -114,6 +114,7 @@
/* convert back to floating value and restore the sign */
if((hx|lx)==0) { /* return sign(x)*0 */
+ q &= 0x7fffffff;
*quo = (sxy ? -q : q);
return Zero[(u_int32_t)sx>>31];
}
@@ -129,9 +130,9 @@
lx = (lx>>n)|((u_int32_t)hx<<(32-n));
hx >>= n;
} else if (n<=31) {
- lx = (hx<<(32-n))|(lx>>n); hx = sx;
+ lx = (hx<<(32-n))|(lx>>n); hx = 0;
} else {
- lx = hx>>(n-32); hx = sx;
+ lx = hx>>(n-32); hx = 0;
}
}
fixup:
>Release-Note:
>Audit-Trail:
>Unformatted:
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