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math: nextafter and nexttoward cleanup

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make nexttoward, nexttowardf independent of long double representation.
fix nextafterl: it did not raise underflow flag when the result was 0.
This commit is contained in:
nsz 2012-05-06 13:08:59 +02:00
commit 6cf865dba6
5 changed files with 176 additions and 291 deletions
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81
src/math/nexttowardf.c
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@ -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;
union fshape ux;
uint32_t e;
GET_FLOAT_WORD(hx, x);
ix = hx & 0x7fffffff; /* |x| */
uy.e = y;
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