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 /*
  27  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  28  * Use is subject to license terms.
  29  */
  30 
  31 #pragma weak __ilogb = ilogb
  32 
  33 #include "libm.h"
  34 #include "xpg6.h"                       /* __xpg6 */
  35 
  36 #if defined(__x86)
  37 static const double two52 = 4503599627370496.0;
  38 #else
  39 /*
  40  * v: high part of a non-zero subnormal |x|; w: low part of |x|
  41  */
  42 static int
  43 ilogb_subnormal(unsigned v, unsigned w)
  44 {
  45         int r = -1022 - 52;
  46 
  47         if (v)
  48                 r += 32;
  49         else
  50                 v = w;
  51 
  52         if (v & 0xffff0000)
  53                 r += 16, v >>= 16;
  54 
  55         if (v & 0xff00)
  56                 r += 8, v >>= 8;
  57 
  58         if (v & 0xf0)
  59                 r += 4, v >>= 4;
  60 
  61         v <<= 1;
  62         return (r + ((0xffffaa50 >> v) & 0x3));
  63 }
  64 #endif /* defined(__x86) */
  65 
  66 static int
  67 raise_invalid(int v)    /* SUSv3 requires ilogb(0,+/-Inf,NaN) raise invalid */
  68 {
  69 #ifndef lint
  70         if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
  71                 static const double zero = 0.0;
  72                 volatile double dummy __unused;
  73 
  74                 dummy = zero / zero;
  75         }
  76 #endif
  77         return (v);
  78 }
  79 
  80 int
  81 ilogb(double x)
  82 {
  83         int *px = (int *)&x, k = px[HIWORD] & ~0x80000000;
  84 
  85         if (k < 0x00100000) {
  86                 if ((px[LOWORD] | k) == 0) {
  87                         return (raise_invalid(0x80000001));
  88                 } else {
  89 #if defined(__x86)
  90                         x *= two52;
  91                         return (((px[HIWORD] & 0x7ff00000) >> 20) - 1075);
  92 #else
  93                         return (ilogb_subnormal(k, px[LOWORD]));
  94 #endif
  95                 }
  96         } else if (k < 0x7ff00000) {
  97                 return ((k >> 20) - 1023);
  98         } else {
  99                 return (raise_invalid(0x7fffffff));
 100         }
 101 }