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  * http://www.algor.co.uk
   8  *
   9  * ########################################################################
  10  *
  11  *  This program is free software; you can distribute it and/or modify it
  12  *  under the terms of the GNU General Public License (Version 2) as
  13  *  published by the Free Software Foundation.
  14  *
  15  *  This program is distributed in the hope it will be useful, but WITHOUT
  16  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  17  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  18  *  for more details.
  19  *
  20  *  You should have received a copy of the GNU General Public License along
  21  *  with this program; if not, write to the Free Software Foundation, Inc.,
  22  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
  23  *
  24  * ########################################################################
  25  */
  26
  27
  28 #include "ieee754sp.h"
  29
  30 ieee754sp ieee754sp_sqrt(ieee754sp x)
  31 {
  32         int ix, s, q, m, t, i;
  33         unsigned int r;
  34         COMPXSP;
  35
  36         /* take care of Inf and NaN */
  37
  38         EXPLODEXSP;
  39         CLEARCX;
  40         FLUSHXSP;
  41
  42         /* x == INF or NAN? */
  43         switch (xc) {
  44         case IEEE754_CLASS_QNAN:
  45                 /* sqrt(Nan) = Nan */
  46                 return ieee754sp_nanxcpt(x, "sqrt");
  47         case IEEE754_CLASS_SNAN:
  48                 SETCX(IEEE754_INVALID_OPERATION);
  49                 return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  50         case IEEE754_CLASS_ZERO:
  51                 /* sqrt(0) = 0 */
  52                 return x;
  53         case IEEE754_CLASS_INF:
  54                 if (xs) {
  55                         /* sqrt(-Inf) = Nan */
  56                         SETCX(IEEE754_INVALID_OPERATION);
  57                         return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  58                 }
  59                 /* sqrt(+Inf) = Inf */
  60                 return x;
  61         case IEEE754_CLASS_DNORM:
  62         case IEEE754_CLASS_NORM:
  63                 if (xs) {
  64                         /* sqrt(-x) = Nan */
  65                         SETCX(IEEE754_INVALID_OPERATION);
  66                         return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
  67                 }
  68                 break;
  69         }
  70
  71         ix = x.bits;
  72
  73         /* normalize x */
  74         m = (ix >> 23);
  75         if (m == 0) {           /* subnormal x */
  76                 for (i = 0; (ix & 0x00800000) == 0; i++)
  77                         ix <<= 1;
  78                 m -= i - 1;
  79         }
  80         m -= 127;               /* unbias exponent */
  81         ix = (ix & 0x007fffff) | 0x00800000;
  82         if (m & 1)              /* odd m, double x to make it even */
  83                 ix += ix;
  84         m >>= 1;                /* m = [m/2] */
  85
  86         /* generate sqrt(x) bit by bit */
  87         ix += ix;
  88         q = s = 0;              /* q = sqrt(x) */
  89         r = 0x01000000;         /* r = moving bit from right to left */
  90
  91         while (r != 0) {
  92                 t = s + r;
  93                 if (t <= ix) {
  94                         s = t + r;
  95                         ix -= t;
  96                         q += r;
  97                 }
  98                 ix += ix;
  99                 r >>= 1;
 100         }
 101
 102         if (ix != 0) {
 103                 SETCX(IEEE754_INEXACT);
 104                 switch (ieee754_csr.rm) {
 105                 case IEEE754_RP:
 106                         q += 2;
 107                         break;
 108                 case IEEE754_RN:
 109                         q += (q & 1);
 110                         break;
 111                 }
 112         }
 113         ix = (q >> 1) + 0x3f000000;
 114         ix += (m << 23);
 115         x.bits = ix;
 116         return x;
 117 }