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  *  This program is free software; you can distribute it and/or modify it
   9  *  under the terms of the GNU General Public License (Version 2) as
  10  *  published by the Free Software Foundation.
  11  *
  12  *  This program is distributed in the hope it will be useful, but WITHOUT
  13  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15  *  for more details.
  16  *
  17  *  You should have received a copy of the GNU General Public License along
  18  *  with this program; if not, write to the Free Software Foundation, Inc.,
  19  *  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA.
  20  */
  21
  22 #include "ieee754sp.h"
  23
  24 union ieee754sp ieee754sp_sqrt(union ieee754sp x)
  25 {
  26         int ix, s, q, m, t, i;
  27         unsigned int r;
  28         COMPXSP;
  29
  30         /* take care of Inf and NaN */
  31
  32         EXPLODEXSP;
  33         ieee754_clearcx();
  34         FLUSHXSP;
  35
  36         /* x == INF or NAN? */
  37         switch (xc) {
  38         case IEEE754_CLASS_SNAN:
  39                 return ieee754sp_nanxcpt(x);
  40
  41         case IEEE754_CLASS_QNAN:
  42                 /* sqrt(Nan) = Nan */
  43                 return x;
  44
  45         case IEEE754_CLASS_ZERO:
  46                 /* sqrt(0) = 0 */
  47                 return x;
  48
  49         case IEEE754_CLASS_INF:
  50                 if (xs) {
  51                         /* sqrt(-Inf) = Nan */
  52                         ieee754_setcx(IEEE754_INVALID_OPERATION);
  53                         return ieee754sp_indef();
  54                 }
  55                 /* sqrt(+Inf) = Inf */
  56                 return x;
  57
  58         case IEEE754_CLASS_DNORM:
  59         case IEEE754_CLASS_NORM:
  60                 if (xs) {
  61                         /* sqrt(-x) = Nan */
  62                         ieee754_setcx(IEEE754_INVALID_OPERATION);
  63                         return ieee754sp_indef();
  64                 }
  65                 break;
  66         }
  67
  68         ix = x.bits;
  69
  70         /* normalize x */
  71         m = (ix >> 23);
  72         if (m == 0) {           /* subnormal x */
  73                 for (i = 0; (ix & 0x00800000) == 0; i++)
  74                         ix <<= 1;
  75                 m -= i - 1;
  76         }
  77         m -= 127;               /* unbias exponent */
  78         ix = (ix & 0x007fffff) | 0x00800000;
  79         if (m & 1)              /* odd m, double x to make it even */
  80                 ix += ix;
  81         m >>= 1;                /* m = [m/2] */
  82
  83         /* generate sqrt(x) bit by bit */
  84         ix += ix;
  85         s = 0;
  86         q = 0;                  /* q = sqrt(x) */
  87         r = 0x01000000;         /* r = moving bit from right to left */
  88
  89         while (r != 0) {
  90                 t = s + r;
  91                 if (t <= ix) {
  92                         s = t + r;
  93                         ix -= t;
  94                         q += r;
  95                 }
  96                 ix += ix;
  97                 r >>= 1;
  98         }
  99
 100         if (ix != 0) {
 101                 ieee754_setcx(IEEE754_INEXACT);
 102                 switch (ieee754_csr.rm) {
 103                 case FPU_CSR_RU:
 104                         q += 2;
 105                         break;
 106                 case FPU_CSR_RN:
 107                         q += (q & 1);
 108                         break;
 109                 }
 110         }
 111         ix = (q >> 1) + 0x3f000000;
 112         ix += (m << 23);
 113         x.bits = ix;
 114         return x;
 115 }