usr/src/lib/libbc/libc/gen/common/ldexp.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License, Version 1.0 only
   6  * (the "License").  You may not use this file except in compliance
   7  * with the License.
   8  *
   9  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
  10  * or http://www.opensolaris.org/os/licensing.
  11  * See the License for the specific language governing permissions
  12  * and limitations under the License.
  13  *
  14  * When distributing Covered Code, include this CDDL HEADER in each
  15  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  16  * If applicable, add the following below this CDDL HEADER, with the
  17  * fields enclosed by brackets "[]" replaced with your own identifying
  18  * information: Portions Copyright [yyyy] [name of copyright owner]
  19  *
  20  * CDDL HEADER END
  21  */
  22 /*
  23  * Copyright 1988 Sun Microsystems, Inc.  All rights reserved.
  24  * Use is subject to license terms.
  25  */
  26
  27 /*      Copyright (c) 1984 AT&T */
  28 /*        All Rights Reserved   */
  29
  30 #pragma ident   "%Z%%M% %I%     %E% SMI"  /* from S5R2 2.7 */
  31
  32 /*LINTLIBRARY*/
  33 /*
  34  *      double ldexp (value, exp)
  35  *              double value;
  36  *              int exp;
  37  *
  38  *      Ldexp returns value * 2**exp, if that result is in range.
  39  *      If underflow occurs, it returns zero.  If overflow occurs,
  40  *      it returns a value of appropriate sign and largest single-
  41  *      precision magnitude.  In case of underflow or overflow,
  42  *      the external int "errno" is set to ERANGE.  Note that errno is
  43  *      not modified if no error occurs, so if you intend to test it
  44  *      after you use ldexp, you had better set it to something
  45  *      other than ERANGE first (zero is a reasonable value to use).
  46  */
  47
  48 #include <values.h>
  49 #include <errno.h>
  50 /* Largest signed long int power of 2 */
  51 #define MAXSHIFT        (BITSPERBYTE * sizeof(long) - 2)
  52
  53 extern double frexp();
  54
  55 double
  56 ldexp(value, exp)
  57 register double value;
  58 register int exp;
  59 {
  60         int old_exp;
  61
  62         if (exp == 0 || value == 0.0) /* nothing to do for zero */
  63                 return (value);
  64 #if     !(pdp11 || u3b5)        /* pdp11 "cc" can't handle cast of
  65                                    double to void on pdp11 or 3b5 */
  66         (void)
  67 #endif
  68         frexp(value, &old_exp);
  69         if (exp > 0) {
  70                 if (exp + old_exp > MAXBEXP) { /* overflow */
  71                         errno = ERANGE;
  72                         return ((double)(value < 0 ? MINDOUBLE : MAXDOUBLE));
  73 /*
  74                         return ((double)(value < 0 ? -1.0e999 : 1.0e999));
  75 */
  76                 }
  77                 for ( ; exp > MAXSHIFT; exp -= MAXSHIFT)
  78                         value *= (1L << MAXSHIFT);
  79                 return (value * (1L << exp));
  80         }
  81         if (exp + old_exp < MINBEXP) { /* underflow */
  82                 errno = ERANGE;
  83                 return (0.0);
  84         }
  85         for ( ; exp < -MAXSHIFT; exp += MAXSHIFT)
  86                 value *= 1.0/(1L << MAXSHIFT); /* mult faster than div */
  87         return (value / (1L << -exp));
  88 }