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Annotation of 43BSDTahoe/usr.lib/libm/floor.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1985 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * Redistribution and use in source and binary forms are permitted
        !             6:  * provided that the above copyright notice and this paragraph are
        !             7:  * duplicated in all such forms and that any documentation,
        !             8:  * advertising materials, and other materials related to such
        !             9:  * distribution and use acknowledge that the software was developed
        !            10:  * by the University of California, Berkeley.  The name of the
        !            11:  * University may not be used to endorse or promote products derived
        !            12:  * from this software without specific prior written permission.
        !            13:  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
        !            14:  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
        !            15:  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
        !            16:  *
        !            17:  * All recipients should regard themselves as participants in an ongoing
        !            18:  * research project and hence should feel obligated to report their
        !            19:  * experiences (good or bad) with these elementary function codes, using
        !            20:  * the sendbug(8) program, to the authors.
        !            21:  */
        !            22: 
        !            23: #ifndef lint
        !            24: static char sccsid[] = "@(#)floor.c    5.4 (Berkeley) 6/30/88";
        !            25: #endif /* not lint */
        !            26: 
        !            27: #if defined(vax)||defined(tahoe)
        !            28: #ifdef vax
        !            29: #define _0x(A,B)       0x/**/A/**/B
        !            30: #else  /* vax */
        !            31: #define _0x(A,B)       0x/**/B/**/A
        !            32: #endif /* vax */
        !            33: static long Lx[] = {_0x(0000,5c00),_0x(0000,0000)};    /* 2**55 */
        !            34: #define L *(double *) Lx
        !            35: #else  /* defined(vax)||defined(tahoe) */
        !            36: static double L = 4503599627370496.0E0;                /* 2**52 */
        !            37: #endif /* defined(vax)||defined(tahoe) */
        !            38: 
        !            39: /*
        !            40:  * floor(x) := the largest integer no larger than x;
        !            41:  * ceil(x) := -floor(-x), for all real x.
        !            42:  *
        !            43:  * Note: Inexact will be signaled if x is not an integer, as is
        !            44:  *     customary for IEEE 754.  No other signal can be emitted.
        !            45:  */
        !            46: double
        !            47: floor(x)
        !            48: double x;
        !            49: {
        !            50:        double y,ceil();
        !            51: 
        !            52:        if (
        !            53: #if !defined(vax)&&!defined(tahoe)
        !            54:                x != x ||       /* NaN */
        !            55: #endif /* !defined(vax)&&!defined(tahoe) */
        !            56:                x >= L)         /* already an even integer */
        !            57:                return x;
        !            58:        else if (x < (double)0)
        !            59:                return -ceil(-x);
        !            60:        else {                  /* now 0 <= x < L */
        !            61:                y = L+x;                /* destructive store must be forced */
        !            62:                y -= L;                 /* an integer, and |x-y| < 1 */
        !            63:                return x < y ? y-(double)1 : y;
        !            64:        }
        !            65: }
        !            66: 
        !            67: double
        !            68: ceil(x)
        !            69: double x;
        !            70: {
        !            71:        double y,floor();
        !            72: 
        !            73:        if (
        !            74: #if !defined(vax)&&!defined(tahoe)
        !            75:                x != x ||       /* NaN */
        !            76: #endif /* !defined(vax)&&!defined(tahoe) */
        !            77:                x >= L)         /* already an even integer */
        !            78:                return x;
        !            79:        else if (x < (double)0)
        !            80:                return -floor(-x);
        !            81:        else {                  /* now 0 <= x < L */
        !            82:                y = L+x;                /* destructive store must be forced */
        !            83:                y -= L;                 /* an integer, and |x-y| < 1 */
        !            84:                return x > y ? y+(double)1 : y;
        !            85:        }
        !            86: }
        !            87: 
        !            88: #ifndef national                       /* rint() is in ./NATIONAL/support.s */
        !            89: /*
        !            90:  * algorithm for rint(x) in pseudo-pascal form ...
        !            91:  *
        !            92:  * real rint(x): real x;
        !            93:  *     ... delivers integer nearest x in direction of prevailing rounding
        !            94:  *     ... mode
        !            95:  * const       L = (last consecutive integer)/2
        !            96:  *       = 2**55; for VAX D
        !            97:  *       = 2**52; for IEEE 754 Double
        !            98:  * real        s,t;
        !            99:  * begin
        !           100:  *     if x != x then return x;                ... NaN
        !           101:  *     if |x| >= L then return x;              ... already an integer
        !           102:  *     s := copysign(L,x);
        !           103:  *     t := x + s;                             ... = (x+s) rounded to integer
        !           104:  *     return t - s
        !           105:  * end;
        !           106:  *
        !           107:  * Note: Inexact will be signaled if x is not an integer, as is
        !           108:  *     customary for IEEE 754.  No other signal can be emitted.
        !           109:  */
        !           110: double
        !           111: rint(x)
        !           112: double x;
        !           113: {
        !           114:        double s,t,one = 1.0,copysign();
        !           115: #if !defined(vax)&&!defined(tahoe)
        !           116:        if (x != x)                             /* NaN */
        !           117:                return (x);
        !           118: #endif /* !defined(vax)&&!defined(tahoe) */
        !           119:        if (copysign(x,one) >= L)               /* already an integer */
        !           120:            return (x);
        !           121:        s = copysign(L,x);
        !           122:        t = x + s;                              /* x+s rounded to integer */
        !           123:        return (t - s);
        !           124: }
        !           125: #endif /* not national */

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