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libc: Prevent infinite recursion when modf is called with NaN or Inf argument. (apply richard millers / modf-nan patch from sources)

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

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

@@ -89,6 +89,16 @@

 	FPdbleword x;

 	int e;

+	x.x = d;

+	e = (x.hi >> SHIFT) & MASK;

+	if(e == MASK){

+		*ip = d;

+		if(x.lo != 0 || (x.hi & 0xfffffL != 0))	/* NaN */

+			return d;

+		/* ±Inf */

+		x.hi &= 0x80000000L;

+		return x.x;

+	}

 	if(d < 1) {

 		if(d < 0) {

 			x.x = modf(-d, ip);

@@ -98,8 +108,7 @@

 		*ip = 0;

 		return d;

 	}

-	x.x = d;

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

+	e -= BIAS;

 	if(e <= SHIFT+1) {

 		x.hi &= ~(0x1fffffL >> e);

 		x.lo = 0;

-- 

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