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frexp: handle NaN values (from sources)

--- a/sys/src/ape/lib/ap/plan9/frexp.c

+++ b/sys/src/ape/lib/ap/plan9/frexp.c

@@ -6,6 +6,7 @@

 #define	MASK	0x7ffL

 #define	SHIFT	20

 #define	BIAS	1022L

+#define	SIG	52

 typedef	union

 {

@@ -25,13 +26,18 @@

 double

 frexp(double d, int *ep)

 {

-	Cheat x;

+	Cheat x, a;

-	if(d == 0) {

-		*ep = 0;

-		return 0;

-	}

+	*ep = 0;

+	/* order matters: only isNaN can operate on NaN */

+	if(isNaN(d) || isInf(d, 0) || d == 0)

+		return d;

 	x.d = d;

+	a.d = fabs(d);

+	if((a.ms >> SHIFT) == 0){	/* normalize subnormal numbers */

+		x.d = (double)(1ULL<<SIG) * d;

+		*ep = -SIG;

+	}

 	*ep = ((x.ms >> SHIFT) & MASK) - BIAS;

 	x.ms &= ~(MASK << SHIFT);

 	x.ms |= BIAS << SHIFT;

--- a/sys/src/libc/port/frexp.c

+++ b/sys/src/libc/port/frexp.c

@@ -9,18 +9,24 @@

 #define	MASK	0x7ffL

 #define	SHIFT	20

 #define	BIAS	1022L

+#define	SIG	52

 double

 frexp(double d, int *ep)

 {

-	FPdbleword x;

+	FPdbleword x, a;

-	if(d == 0) {

-		*ep = 0;

-		return 0;

-	}

+	*ep = 0;

+	/* order matters: only isNaN can operate on NaN */

+	if(isNaN(d) || isInf(d, 0) || d == 0)

+		return d;

 	x.x = d;

-	*ep = ((x.hi >> SHIFT) & MASK) - BIAS;

+	a.x = fabs(d);

+	if((a.hi >> SHIFT) == 0){	/* normalize subnormal numbers */

+		x.x = (double)(1ULL<<SIG) * d;

+		*ep = -SIG;

+	}

+	*ep += ((x.hi >> SHIFT) & MASK) - BIAS;

 	x.hi &= ~(MASK << SHIFT);

 	x.hi |= BIAS << SHIFT;

 	return x.x;

-- 

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