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sp_sqrt.c

/* IEEE754 floating point arithmetic
 * single precision square root
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 * http://www.algor.co.uk
 *
 * ########################################################################
 *
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License (Version 2) as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * ########################################################################
 */


#include "ieee754sp.h"

ieee754sp ieee754sp_sqrt(ieee754sp x)
{
      int ix, s, q, m, t, i;
      unsigned int r;
      COMPXSP;

      /* take care of Inf and NaN */

      EXPLODEXSP;
      CLEARCX;
      FLUSHXSP;

      /* x == INF or NAN? */
      switch (xc) {
      case IEEE754_CLASS_QNAN:
            /* sqrt(Nan) = Nan */
            return ieee754sp_nanxcpt(x, "sqrt");
      case IEEE754_CLASS_SNAN:
            SETCX(IEEE754_INVALID_OPERATION);
            return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
      case IEEE754_CLASS_ZERO:
            /* sqrt(0) = 0 */
            return x;
      case IEEE754_CLASS_INF:
            if (xs) {
                  /* sqrt(-Inf) = Nan */
                  SETCX(IEEE754_INVALID_OPERATION);
                  return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
            }
            /* sqrt(+Inf) = Inf */
            return x;
      case IEEE754_CLASS_DNORM:
      case IEEE754_CLASS_NORM:
            if (xs) {
                  /* sqrt(-x) = Nan */
                  SETCX(IEEE754_INVALID_OPERATION);
                  return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
            }
            break;
      }

      ix = x.bits;

      /* normalize x */
      m = (ix >> 23);
      if (m == 0) {           /* subnormal x */
            for (i = 0; (ix & 0x00800000) == 0; i++)
                  ix <<= 1;
            m -= i - 1;
      }
      m -= 127;         /* unbias exponent */
      ix = (ix & 0x007fffff) | 0x00800000;
      if (m & 1)        /* odd m, double x to make it even */
            ix += ix;
      m >>= 1;          /* m = [m/2] */

      /* generate sqrt(x) bit by bit */
      ix += ix;
      q = s = 0;        /* q = sqrt(x) */
      r = 0x01000000;         /* r = moving bit from right to left */

      while (r != 0) {
            t = s + r;
            if (t <= ix) {
                  s = t + r;
                  ix -= t;
                  q += r;
            }
            ix += ix;
            r >>= 1;
      }

      if (ix != 0) {
            SETCX(IEEE754_INEXACT);
            switch (ieee754_csr.rm) {
            case IEEE754_RP:
                  q += 2;
                  break;
            case IEEE754_RN:
                  q += (q & 1);
                  break;
            }
      }
      ix = (q >> 1) + 0x3f000000;
      ix += (m << 23);
      x.bits = ix;
      return x;
}

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