arch/mips/math-emu/sp_sqrt.c

   1 /* IEEE754 floating point arithmetic
   2  * single precision square root
   3  */
   4 /*
   5  * MIPS floating point support
   6  * Copyright (C) 1994-2000 Algorithmics Ltd.
   7  *
   8  * ########################################################################
   9  *
  10  *  This program is free software; you can distribute it and/or modify it
  11  *  under the terms of the GNU General Public License (Version 2) as
  12  *  published by the Free Software Foundation.
  13  *
  14  *  This program is distributed in the hope it will be useful, but WITHOUT
  15  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  16  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  17  *  for more details.
  18  *
  19  *  You should have received a copy of the GNU General Public License along
  20  *  with this program; if not, write to the Free Software Foundation, Inc.,
  21  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
  22  *
  23  * ########################################################################
  24  */
  25
  26
  27 #include "ieee754sp.h"
  28
  29 ieee754sp ieee754sp_sqrt(ieee754sp x)
  30 {
  31         int ix, s, q, m, t, i;
  32         unsigned int r;
  33         COMPXSP;
  34
  35         /* take care of Inf and NaN */
  36
  37         EXPLODEXSP;
  38         CLEARCX;
  39         FLUSHXSP;
  40
  41         /* x == INF or NAN? */
  42         switch (xc) {
  43         case IEEE754_CLASS_QNAN:
  44                 /* sqrt(Nan) = Nan */
  45                 return ieee754sp_nanxcpt(x, "sqrt");
  46         case IEEE754_CLASS_SNAN:
  47                 SETCX(IEEE754_INVALID_OPERATION);
  48                 return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  49         case IEEE754_CLASS_ZERO:
  50                 /* sqrt(0) = 0 */
  51                 return x;
  52         case IEEE754_CLASS_INF:
  53                 if (xs) {
  54                         /* sqrt(-Inf) = Nan */
  55                         SETCX(IEEE754_INVALID_OPERATION);
  56                         return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  57                 }
  58                 /* sqrt(+Inf) = Inf */
  59                 return x;
  60         case IEEE754_CLASS_DNORM:
  61         case IEEE754_CLASS_NORM:
  62                 if (xs) {
  63                         /* sqrt(-x) = Nan */
  64                         SETCX(IEEE754_INVALID_OPERATION);
  65                         return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  66                 }
  67                 break;
  68         }
  69
  70         ix = x.bits;
  71
  72         /* normalize x */
  73         m = (ix >> 23);
  74         if (m == 0) {           /* subnormal x */
  75                 for (i = 0; (ix & 0x00800000) == 0; i++)
  76                         ix <<= 1;
  77                 m -= i - 1;
  78         }
  79         m -= 127;               /* unbias exponent */
  80         ix = (ix & 0x007fffff) | 0x00800000;
  81         if (m & 1)              /* odd m, double x to make it even */
  82                 ix += ix;
  83         m >>= 1;                /* m = [m/2] */
  84
  85         /* generate sqrt(x) bit by bit */
  86         ix += ix;
  87         q = s = 0;              /* q = sqrt(x) */
  88         r = 0x01000000;         /* r = moving bit from right to left */
  89
  90         while (r != 0) {
  91                 t = s + r;
  92                 if (t <= ix) {
  93                         s = t + r;
  94                         ix -= t;
  95                         q += r;
  96                 }
  97                 ix += ix;
  98                 r >>= 1;
  99         }
 100
 101         if (ix != 0) {
 102                 SETCX(IEEE754_INEXACT);
 103                 switch (ieee754_csr.rm) {
 104                 case IEEE754_RP:
 105                         q += 2;
 106                         break;
 107                 case IEEE754_RN:
 108                         q += (q & 1);
 109                         break;
 110                 }
 111         }
 112         ix = (q >> 1) + 0x3f000000;
 113         ix += (m << 23);
 114         x.bits = ix;
 115         return x;
 116 }