math: nextafter and nexttoward cleanup

make nexttoward, nexttowardf independent of long double representation.
fix nextafterl: it did not raise underflow flag when the result was 0.

1 files changed, 28 insertions, 53 deletions

diff --git a/src/math/nexttowardf.c b/src/math/nexttowardf.c
index c52ef3aa..821f72a5 100644
--- a/src/math/nexttowardf.c
+++ b/src/math/nexttowardf.c
@@ -1,62 +1,37 @@
-/* origin: FreeBSD /usr/src/lib/msun/src/s_nexttowardf.c */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
- */
-
 #include "libm.h"
 
-#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
-// FIXME
-#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-#define LDBL_INFNAN_EXP (LDBL_MAX_EXP * 2 - 1)
-
 float nexttowardf(float x, long double y)
 {
-	union IEEEl2bits uy;
-	volatile float t;
-	int32_t hx,ix;
-
-	GET_FLOAT_WORD(hx, x);
-	ix = hx & 0x7fffffff;  /* |x| */
-	uy.e = y;
+	union fshape ux;
+	uint32_t e;
 
-	if (ix > 0x7f800000 ||
-	    (uy.bits.exp == LDBL_INFNAN_EXP &&
-	     ((uy.bits.manh&~LDBL_NBIT)|uy.bits.manl) != 0))
-		return x + y;  /* x or y is nan */
+	if (isnan(x) || isnan(y))
+		return x + y;
 	if (x == y)
-		return (float)y;  /* x=y, return y */
-	if (ix == 0) {   /* x == 0 */
-		SET_FLOAT_WORD(x, (uy.bits.sign<<31)|1); /* return +-minsubnormal */
-		/* raise underflow flag */
-		t = x*x;
-		if (t == x)
-			return t;
-		return x;
+		return y;
+	ux.value = x;
+	if (x == 0) {
+		ux.bits = 1;
+		if (signbit(y))
+			ux.bits |= 0x80000000;
+	} else if (x < y) {
+		if (signbit(x))
+			ux.bits--;
+		else
+			ux.bits++;
+	} else {
+		if (signbit(x))
+			ux.bits++;
+		else
+			ux.bits--;
 	}
-	if (hx >= 0 ^ x < y)  /* x -= ulp */
-		hx--;
-	else                  /* x += ulp */
-		hx++;
-	ix = hx & 0x7f800000;
-	if (ix >= 0x7f800000)  /* overflow  */
-		return x+x;
-	if (ix < 0x00800000) { /* underflow */
-		/* raise underflow flag */
-		t = x*x;
-		if (t != x) {
-			SET_FLOAT_WORD(x, hx);
-			return x;
-		}
+	e = ux.bits & 0x7f800000;
+	/* raise overflow if ux.value is infinite and x is finite */
+	if (e == 0x7f800000)
+		return x + x;
+	/* raise underflow if ux.value is subnormal or zero */
+	if (e == 0) {
+		volatile float z = x*x + ux.value*ux.value;
 	}
-	SET_FLOAT_WORD(x, hx);
-	return x;
+	return ux.value;
 }
-#endif