[9front] ape modf infinite recursion

[9front] ape modf infinite recursion

[Xiao-Yong Jin]

modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78

[9front] Re: ape modf infinite recursion

[Anthony Martin]

Xiao-Yong Jin <meta.jxy@gmail.com> once said:
> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78

There was a fix to this on sources that was
apparently never picked up by 9front.

I've included it below but you can also find
it in David du Colombier's mirror:

https://github.com/0intro/plan9/commit/119c1d0c712512776162de1eca755006f07fe91c

Cheers,
  Anthony

diff --git a/sys/src/ape/lib/ap/plan9/frexp.c b/sys/src/ape/lib/ap/plan9/frexp.c
--- a/sys/src/ape/lib/ap/plan9/frexp.c
+++ b/sys/src/ape/lib/ap/plan9/frexp.c
@@ -73,6 +73,16 @@
 	Cheat x;
 	int e;

+	x.d = d;
+	e = (x.ms >> SHIFT) & MASK;
+	if(e == MASK){
+		*ip = d;
+		if(x.ls != 0 || (x.ms & 0xfffffL) != 0)	/* NaN */
+			return d;
+		/* ±Inf */
+		x.ms &= 0x80000000L;
+		return x.d;
+	}
 	if(d < 1) {
 		if(d < 0) {
 			f = modf(-d, ip);
@@ -82,8 +92,7 @@
 		*ip = 0;
 		return d;
 	}
-	x.d = d;
-	e = ((x.ms >> SHIFT) & MASK) - BIAS;
+	e -= BIAS;
 	if(e <= SHIFT+1) {
 		x.ms &= ~(0x1fffffL >> e);
 		x.ls = 0;

Re: [9front] ape modf infinite recursion

[Xiao-Yong Jin]

> On Jan 21, 2021, at 10:20 PM, Anthony Martin <ality@pbrane.org> wrote:
> 
> Xiao-Yong Jin <meta.jxy@gmail.com> once said:
>> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
>> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
>> modf(ip=0x7fffffffe9e8,d=0xffffffffffffffff)+0x43 /sys/src/ape/lib/ap/plan9/frexp.c:78
> 
> There was a fix to this on sources that was
> apparently never picked up by 9front.
> 
> I've included it below but you can also find
> it in David du Colombier's mirror:
> 
> https://github.com/0intro/plan9/commit/119c1d0c712512776162de1eca755006f07fe91c

The one at
	/sys/src/libc/port/frexp.c
seems up-to-date with that, but not the ape one.

I borrowed the one from musl
	https://git.musl-libc.org/cgit/musl/tree/src/math/modf.c
to ape, which seems to behave better.

Re: [9front] ape modf infinite recursion

[Xiao-Yong Jin]

There is another ancient stray copy of modf
	/sys/src/ape/lib/ap/math/modf.c
which is not in the mkfile.

Re: [9front] ape modf infinite recursion

[cinap_lenrek]

you are correct. this fix has been applied previously
to plan9 libc, but was missed the ape version.

applied! thank you!

--
cinap

Re: [9front] ape modf infinite recursion

[Alex Musolino]

We might need an isNaN check in there but it looks like we're also
generating the wrong code for the <0 comparison.  6c emits UCOMISD
followed by JCC.  The UCOMISD will set all three ZF, PF, CF flags to 1
when either operand is NaN to indicate there is no ordering, but the
JCC only looks at CF and incorrectly determines that NaN < 0.