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 __ilogbf = ilogbf
  32 
  33 #include "libm.h"
  34 #include "xpg6.h"                       /* __xpg6 */
  35 
  36 #if defined(__x86)
  37 static const float two25 = 33554432.0F;
  38 #else
  39 /*
  40  * v: a non-zero subnormal |x|
  41  */
  42 static int
  43 ilogbf_subnormal(unsigned v)
  44 {
  45         int r = -126 - 23;
  46 
  47         if (v & 0xffff0000)
  48                 r += 16, v >>= 16;
  49 
  50         if (v & 0xff00)
  51                 r += 8, v >>= 8;
  52 
  53         if (v & 0xf0)
  54                 r += 4, v >>= 4;
  55 
  56         v <<= 1;
  57         return (r + ((0xffffaa50 >> v) & 0x3));
  58 }
  59 #endif /* defined(__x86) */
  60 
  61 static int
  62 raise_invalid(int v)   /* SUSv3 requires ilogbf(0,+/-Inf,NaN) raise invalid */
  63 {
  64 #ifndef lint
  65         if ((__xpg6 & _C99SUSv3_ilogb_0InfNaN_raises_invalid) != 0) {
  66                 static const double zero = 0.0;
  67                 volatile double dummy __unused;
  68 
  69                 dummy = zero / zero;
  70         }
  71 #endif
  72         return (v);
  73 }
  74 
  75 int
  76 ilogbf(float x)
  77 {
  78         int k = *((int *)&x) & ~0x80000000;
  79 
  80         if (k < 0x00800000) {
  81                 if (k == 0) {
  82                         return (raise_invalid(0x80000001));
  83                 } else {
  84 #if defined(__x86)
  85                         x *= two25;
  86                         return (((*((int *)&x) & 0x7f800000) >> 23) - 152);
  87 #else
  88                         return (ilogbf_subnormal(k));
  89 #endif
  90                 }
  91         } else if (k < 0x7f800000) {
  92                 return ((k >> 23) - 127);
  93         } else {
  94                 return (raise_invalid(0x7fffffff));
  95         }
  96 }