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Annotation of src/lib/libm/src/s_ceil.c, Revision 1.2

1.1       jtc         1:
                      2: /* @(#)s_ceil.c 5.1 93/09/24 */
                      3: /*
                      4:  * ====================================================
                      5:  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
                      6:  *
                      7:  * Developed at SunPro, a Sun Microsystems, Inc. business.
                      8:  * Permission to use, copy, modify, and distribute this
                      9:  * software is freely granted, provided that this notice
                     10:  * is preserved.
                     11:  * ====================================================
                     12:  */
                     13:
                     14: /*
                     15:  * ceil(x)
                     16:  * Return x rounded toward -inf to integral value
                     17:  * Method:
                     18:  *     Bit twiddling.
                     19:  * Exception:
                     20:  *     Inexact flag raised if x not equal to ceil(x).
                     21:  */
                     22:
1.2     ! jtc        23: #include <math.h>
1.1       jtc        24:
                     25: #ifdef __STDC__
                     26: static const double one = 1.0,huge = 1.0e300;
                     27: #else
                     28: static double one = 1.0,huge = 1.0e300;
                     29: #endif
                     30:
                     31: #ifdef __STDC__
                     32:        double ceil(double x)
                     33: #else
                     34:        double ceil(x)
                     35:        double x;
                     36: #endif
                     37: {
                     38:        int i0,i1,n0,j0;
                     39:        unsigned i,j;
                     40:        n0 = (*((int *)&one)>>29)^1;
                     41:        i0 =  *(n0+(int*)&x);
                     42:        i1 =  *(1-n0+(int*)&x);
                     43:        j0 = ((i0>>20)&0x7ff)-0x3ff;
                     44:        if(j0<20) {
                     45:            if(j0<0) {  /* raise inexact if x != 0 */
                     46:                if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
                     47:                    if(i0<0) {i0=0x80000000;i1=0;}
                     48:                    else if((i0|i1)!=0) { i0=0x3ff00000;i1=0;}
                     49:                }
                     50:            } else {
                     51:                i = (0x000fffff)>>j0;
                     52:                if(((i0&i)|i1)==0) return x; /* x is integral */
                     53:                if(huge+x>0.0) {        /* raise inexact flag */
                     54:                    if(i0>0) i0 += (0x00100000)>>j0;
                     55:                    i0 &= (~i); i1=0;
                     56:                }
                     57:            }
                     58:        } else if (j0>51) {
                     59:            if(j0==0x400) return x+x;   /* inf or NaN */
                     60:            else return x;              /* x is integral */
                     61:        } else {
                     62:            i = ((unsigned)(0xffffffff))>>(j0-20);
                     63:            if((i1&i)==0) return x;     /* x is integral */
                     64:            if(huge+x>0.0) {            /* raise inexact flag */
                     65:                if(i0>0) {
                     66:                    if(j0==20) i0+=1;
                     67:                    else {
                     68:                        j = i1 + (1<<(52-j0));
                     69:                        if(j<i1) i0+=1; /* got a carry */
                     70:                        i1 = j;
                     71:                    }
                     72:                }
                     73:                i1 &= (~i);
                     74:            }
                     75:        }
                     76:        *(n0+(int*)&x) = i0;
                     77:        *(1-n0+(int*)&x) = i1;
                     78:        return x;
                     79: }

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