LXR linux/arch/mips/math-emu/sp

   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
  30ieee754sp 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}
 118