usr/src/lib/libm/common/R/ilogbf.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 ilogbf = __ilogbf
  31
  32 #include "libm.h"
  33 #include "xpg6.h"       /* __xpg6 */
  34
  35 #if defined(__x86)
  36 static const float two25 = 33554432.0F;
  37 #else
  38 /*
  39  * v: a non-zero subnormal |x|
  40  */
  41 static int
  42 ilogbf_subnormal(unsigned v) {
  43         int r = -126 - 23;
  44
  45         if (v & 0xffff0000)
  46                 r += 16, v >>= 16;
  47         if (v & 0xff00)
  48                 r += 8, v >>= 8;
  49         if (v & 0xf0)
  50                 r += 4, v >>= 4;
  51         v <<= 1;
  52         return (r + ((0xffffaa50 >> v) & 0x3));
  53 }
  54 #endif  /* defined(__x86) */
  55
  56 static int
  57 raise_invalid(int v) {  /* SUSv3 requires ilogbf(0,+/-Inf,NaN) raise invalid */
  58 #ifndef lint
  59         if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
  60                 static const double zero = 0.0;
  61                 volatile double dummy;
  62
  63                 dummy = zero / zero;
  64         }
  65 #endif
  66         return (v);
  67 }
  68
  69 int
  70 ilogbf(float x) {
  71         int k = *((int *) &x) & ~0x80000000;
  72
  73         if (k < 0x00800000) {
  74                 if (k == 0)
  75                         return (raise_invalid(0x80000001));
  76                 else {
  77 #if defined(__x86)
  78                         x *= two25;
  79                         return (((*((int *) &x) & 0x7f800000) >> 23) - 152);
  80 #else
  81                         return (ilogbf_subnormal(k));
  82 #endif
  83                 }
  84         } else if (k < 0x7f800000)
  85                 return ((k >> 23) - 127);
  86         else
  87                 return (raise_invalid(0x7fffffff));
  88 }