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Date: Thu, 21 Jan 2021 20:20:43 -0800
From: Anthony Martin <ality@pbrane.org>
To: 9front@9front.org
Message-ID: <YApSm3KPXx3M1qqF@alice>
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Subject: [9front] Re: ape modf infinite recursion
Reply-To: 9front@9front.org
Precedence: bulk

Xiao-Yong Jin <meta.jxy@gmail.com> once said:
> modf(ip=3D0x7fffffffe9e8,d=3D0xffffffffffffffff)+0x43 /sys/src/ape/lib/=
ap/plan9/frexp.c:78
> modf(ip=3D0x7fffffffe9e8,d=3D0xffffffffffffffff)+0x43 /sys/src/ape/lib/=
ap/plan9/frexp.c:78
> modf(ip=3D0x7fffffffe9e8,d=3D0xffffffffffffffff)+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/119c1d0c712512776162de1eca755006f0=
7fe91c

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 =3D d;
+	e =3D (x.ms >> SHIFT) & MASK;
+	if(e =3D=3D MASK){
+		*ip =3D d;
+		if(x.ls !=3D 0 || (x.ms & 0xfffffL) !=3D 0)	/* NaN */
+			return d;
+		/* =C2=B1Inf */
+		x.ms &=3D 0x80000000L;
+		return x.d;
+	}
 	if(d < 1) {
 		if(d < 0) {
 			f =3D modf(-d, ip);
@@ -82,8 +92,7 @@
 		*ip =3D 0;
 		return d;
 	}
-	x.d =3D d;
-	e =3D ((x.ms >> SHIFT) & MASK) - BIAS;
+	e -=3D BIAS;
 	if(e <=3D SHIFT+1) {
 		x.ms &=3D ~(0x1fffffL >> e);
 		x.ls =3D 0;