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 *  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
  24union 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}
 116