usr/src/lib/libm/common/Q/scalbnl.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 (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21
  22 /*
  23  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  24  */
  25 /*
  26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  27  * Use is subject to license terms.
  28  */
  29
  30 #pragma weak __scalbnl = scalbnl
  31
  32 #include "libm.h"
  33 #include <float.h>              /* LDBL_MAX, LDBL_MIN */
  34 #include <stdlib.h>             /* abs */
  35
  36 #if defined(__sparc)
  37 #define XSET_EXP(k, x)  ((int *) &x)[0] = (((int *) &x)[0] & ~0x7fff0000) | \
  38                                 (k << 16)
  39 #define ISINFNANL(k, x) (k == 0x7fff)
  40 #define XTWOT_OFFSET    113
  41 static const long double xtwot = 10384593717069655257060992658440192.0L,
  42                                                                 /* 2^113 */
  43         twomtm1 = 4.814824860968089632639944856462318296E-35L;  /* 2^-114 */
  44 #elif defined(__x86)
  45 #define XSET_EXP(k, x)  ((int *) &x)[2] = (((int *) &x)[2] & ~0x7fff) | k
  46 #if defined(HANDLE_UNSUPPORTED)
  47 #define ISINFNANL(k, x) (k == 0x7fff || k != 0 && \
  48                                 (((int *) &x)[1] & 0x80000000) == 0)
  49 #else
  50 #define ISINFNANL(k, x) (k == 0x7fff)
  51 #endif
  52 #define XTWOT_OFFSET    64
  53 static const long double xtwot = 18446744073709551616.0L,       /* 2^64 */
  54         twomtm1 = 2.7105054312137610850186E-20L;                /* 2^-65 */
  55 #endif
  56
  57 long double
  58 scalbnl(long double x, int n) {
  59         int k = XBIASED_EXP(x);
  60
  61         if (ISINFNANL(k, x))
  62                 return (x + x);
  63         if (ISZEROL(x) || n == 0)
  64                 return (x);
  65         if (k == 0) {
  66                 x *= xtwot;
  67                 k = XBIASED_EXP(x) - XTWOT_OFFSET;
  68         }
  69         if ((unsigned) abs(n) >= 131072)        /* cast to unsigned for -2^31 */
  70                 n >>= 1;                /* avoid subsequent integer overflow */
  71         k += n;
  72         if (k > 0x7ffe)
  73                 return (LDBL_MAX * copysignl(LDBL_MAX, x));
  74         if (k <= -XTWOT_OFFSET - 1)
  75                 return (LDBL_MIN * copysignl(LDBL_MIN, x));
  76         if (k > 0) {
  77                 XSET_EXP(k, x);
  78                 return (x);
  79         }
  80         k += XTWOT_OFFSET + 1;
  81         XSET_EXP(k, x);
  82         return (x * twomtm1);
  83 }