Name: Anonymous 2011-06-01 13:00
how is it implemented
/* s_ceill.c -- long double version of s_ceil.c.
* Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
*/
/*
* ====================================================
* 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.
* ====================================================
*/
#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: $";
#endif
/*
* ceill(x)
* Return x rounded toward -inf to integral value
* Method:
* Bit twiddling.
* Exception:
* Inexact flag raised if x not equal to ceil(x).
*/
#include "math.h"
#include "math_private.h"
#ifdef __STDC__
static const long double huge = 1.0e4930;
#else
static long double huge = 1.0e4930;
#endif
#ifdef __STDC__
long double __ceill(long double x)
#else
long double __ceill(x)
long double x;
#endif
{
int64_t i0,i1,j0;
u_int64_t i,j;
GET_LDOUBLE_WORDS64(i0,i1,x);
j0 = ((i0>>48)&0x7fff)-0x3fff;
if(j0<48) {
if(j0<0) { /* raise inexact if x != 0 */
if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
if(i0<0) {i0=0x8000000000000000ULL;i1=0;}
else if((i0|i1)!=0) { i0=0x3fff000000000000ULL;i1=0;}
}
} else {
i = (0x0000ffffffffffffULL)>>j0;
if(((i0&i)|i1)==0) return x; /* x is integral */
if(huge+x>0.0) { /* raise inexact flag */
if(i0>0) i0 += (0x0001000000000000LL)>>j0;
i0 &= (~i); i1=0;
}
}
} else if (j0>111) {
if(j0==0x4000) return x+x; /* inf or NaN */
else return x; /* x is integral */
} else {
i = -1ULL>>(j0-48);
if((i1&i)==0) return x; /* x is integral */
if(huge+x>0.0) { /* raise inexact flag */
if(i0>0) {
if(j0==48) i0+=1;
else {
j = i1+(1LL<<(112-j0));
if(j<i1) i0 +=1 ; /* got a carry */
i1=j;
}
}
i1 &= (~i);
}
}
SET_LDOUBLE_WORDS64(x,i0,i1);
return x;
}
weak_alias (__ceill, ceill)