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 *
   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
  29ieee754sp 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}
 117