The helpers for x86/amd64 fprem and fprem1 in target-i386/helper.c are
significantly borked and, for example, cause konqueror in RedHat8 (x86
guest) to go into an infinite loop when displaying http://news.bbc.co.uk.
helper_fprem has the following borkage:
- various Inf/Nan/zero inputs not handled correctly
- incorrect rounding when converting negative 'dblq' to 'q'
- incorrect order of assignment to C bits (0,3,1 not 0,1,3)
helper_fprem1 has those problems and is also incorrect about the points
at which its rounding needs to differ from that of helper_fprem.
Patch below fixes all these. It brings the fprem and fprem1 behaviour
very much closer to the hardware -- not identical, but close. Some
+0.0 results should really be -0.0 and there may still be other differences.
Anyway konquerer no longer loops with the patch applied.
J
--- ../Orig/qemu-0.9.0/target-i386/helper.c 2007-02-05 23:01:54.000000000 +0000
+++ target-i386/helper.c 2007-03-17 17:21:02.000000000 +0000
@@ -3097,30 +3097,51 @@
CPU86_LDouble dblq, fpsrcop, fptemp;
CPU86_LDoubleU fpsrcop1, fptemp1;
int expdif;
- int q;
+ signed long long int q;
+
+ if (isinf(ST0) || isnan(ST0) || isnan(ST1) || (ST1 == 0.0)) {
+ ST0 = 0.0 / 0.0; /* NaN */
+ env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
+ return;
+ }
fpsrcop = ST0;
fptemp = ST1;
fpsrcop1.d = fpsrcop;
fptemp1.d = fptemp;
expdif = EXPD(fpsrcop1) - EXPD(fptemp1);
+
+ if (expdif < 0) {
+ /* optimisation? taken from the AMD docs */
+ env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
+ /* ST0 is unchanged */
+ return;
+ }
+
if (expdif < 53) {
dblq = fpsrcop / fptemp;
- dblq = (dblq < 0.0)? ceil(dblq): floor(dblq);
+ /* round dblq towards nearest integer */
+ dblq = rint(dblq);
ST0 = fpsrcop - fptemp*dblq;
- q = (int)dblq; /* cutting off top bits is assumed here */
+
+ /* convert dblq to q by truncating towards zero */
+ if (dblq < 0.0)
+ q = (signed long long int)(-dblq);
+ else
+ q = (signed long long int)dblq;
+
env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
- /* (C0,C1,C3) <-- (q2,q1,q0) */
- env->fpus |= (q&0x4) << 6; /* (C0) <-- q2 */
- env->fpus |= (q&0x2) << 8; /* (C1) <-- q1 */
- env->fpus |= (q&0x1) << 14; /* (C3) <-- q0 */
+ /* (C0,C3,C1) <-- (q2,q1,q0) */
+ env->fpus |= (q&0x4) << (8-2); /* (C0) <-- q2 */
+ env->fpus |= (q&0x2) << (14-1); /* (C3) <-- q1 */
+ env->fpus |= (q&0x1) << (9-0); /* (C1) <-- q0 */
} else {
env->fpus |= 0x400; /* C2 <-- 1 */
fptemp = pow(2.0, expdif-50);
fpsrcop = (ST0 / ST1) / fptemp;
- /* fpsrcop = integer obtained by rounding to the nearest */
- fpsrcop = (fpsrcop-floor(fpsrcop) < ceil(fpsrcop)-fpsrcop)?
- floor(fpsrcop): ceil(fpsrcop);
+ /* fpsrcop = integer obtained by chopping */
+ fpsrcop = (fpsrcop < 0.0)?
+ -(floor(fabs(fpsrcop))): floor(fpsrcop);
ST0 -= (ST1 * fpsrcop * fptemp);
}
}
@@ -3130,26 +3151,48 @@
CPU86_LDouble dblq, fpsrcop, fptemp;
CPU86_LDoubleU fpsrcop1, fptemp1;
int expdif;
- int q;
-
- fpsrcop = ST0;
- fptemp = ST1;
+ signed long long int q;
+
+ if (isinf(ST0) || isnan(ST0) || isnan(ST1) || (ST1 == 0.0)) {
+ ST0 = 0.0 / 0.0; /* NaN */
+ env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
+ return;
+ }
+
+ fpsrcop = (CPU86_LDouble)ST0;
+ fptemp = (CPU86_LDouble)ST1;
fpsrcop1.d = fpsrcop;
fptemp1.d = fptemp;
expdif = EXPD(fpsrcop1) - EXPD(fptemp1);
+
+ if (expdif < 0) {
+ /* optimisation? taken from the AMD docs */
+ env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
+ /* ST0 is unchanged */
+ return;
+ }
+
if ( expdif < 53 ) {
- dblq = fpsrcop / fptemp;
+ dblq = fpsrcop/*ST0*/ / fptemp/*ST1*/;
+ /* round dblq towards zero */
dblq = (dblq < 0.0)? ceil(dblq): floor(dblq);
- ST0 = fpsrcop - fptemp*dblq;
- q = (int)dblq; /* cutting off top bits is assumed here */
+ ST0 = fpsrcop/*ST0*/ - fptemp*dblq;
+
+ /* convert dblq to q by truncating towards zero */
+ if (dblq < 0.0)
+ q = (signed long long int)(-dblq);
+ else
+ q = (signed long long int)dblq;
+
env->fpus &= (~0x4700); /* (C3,C2,C1,C0) <-- 0000 */
- /* (C0,C1,C3) <-- (q2,q1,q0) */
- env->fpus |= (q&0x4) << 6; /* (C0) <-- q2 */
- env->fpus |= (q&0x2) << 8; /* (C1) <-- q1 */
- env->fpus |= (q&0x1) << 14; /* (C3) <-- q0 */
+ /* (C0,C3,C1) <-- (q2,q1,q0) */
+ env->fpus |= (q&0x4) << (8-2); /* (C0) <-- q2 */
+ env->fpus |= (q&0x2) << (14-1); /* (C3) <-- q1 */
+ env->fpus |= (q&0x1) << (9-0); /* (C1) <-- q0 */
} else {
+ int N = 32 + (expdif % 32); /* as per AMD docs */
env->fpus |= 0x400; /* C2 <-- 1 */
- fptemp = pow(2.0, expdif-50);
+ fptemp = pow(2.0, (double)(expdif-N));
fpsrcop = (ST0 / ST1) / fptemp;
/* fpsrcop = integer obtained by chopping */
fpsrcop = (fpsrcop < 0.0)?
_______________________________________________
Qemu-devel mailing list
Qemu-devel@nongnu.org
http://lists.nongnu.org/mailman/listinfo/qemu-devel
