cordic.c

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    1 /*
    2  * Copyright (c) 2011 Broadcom Corporation
    3  *
    4  * Permission to use, copy, modify, and/or distribute this software for any
    5  * purpose with or without fee is hereby granted, provided that the above
    6  * copyright notice and this permission notice appear in all copies.
    7  *
    8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   11  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
   13  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   14  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   15  */
   16 #include <linux/module.h>
   17 #include <linux/cordic.h>
   18 
   19 #define CORDIC_ANGLE_GEN        39797
   20 #define CORDIC_PRECISION_SHIFT  16
   21 #define CORDIC_NUM_ITER         (CORDIC_PRECISION_SHIFT + 2)
   22 
   23 #define FIXED(X)        ((s32)((X) << CORDIC_PRECISION_SHIFT))
   24 #define FLOAT(X)        (((X) >= 0) \
   25                 ? ((((X) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1) \
   26                 : -((((-(X)) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1))
   27 
   28 static const s32 arctan_table[] = {
   29         2949120,
   30         1740967,
   31         919879,
   32         466945,
   33         234379,
   34         117304,
   35         58666,
   36         29335,
   37         14668,
   38         7334,
   39         3667,
   40         1833,
   41         917,
   42         458,
   43         229,
   44         115,
   45         57,
   46         29
   47 };
   48 
   49 /*
   50  * cordic_calc_iq() - calculates the i/q coordinate for given angle
   51  *
   52  * theta: angle in degrees for which i/q coordinate is to be calculated
   53  * coord: function output parameter holding the i/q coordinate
   54  */
   55 struct cordic_iq cordic_calc_iq(s32 theta)
   56 {
   57         struct cordic_iq coord;
   58         s32 angle, valtmp;
   59         unsigned iter;
   60         int signx = 1;
   61         int signtheta;
   62 
   63         coord.i = CORDIC_ANGLE_GEN;
   64         coord.q = 0;
   65         angle = 0;
   66 
   67         theta = FIXED(theta);
   68         signtheta = (theta < 0) ? -1 : 1;
   69         theta = ((theta + FIXED(180) * signtheta) % FIXED(360)) -
   70                 FIXED(180) * signtheta;
   71 
   72         if (FLOAT(theta) > 90) {
   73                 theta -= FIXED(180);
   74                 signx = -1;
   75         } else if (FLOAT(theta) < -90) {
   76                 theta += FIXED(180);
   77                 signx = -1;
   78         }
   79 
   80         for (iter = 0; iter < CORDIC_NUM_ITER; iter++) {
   81                 if (theta > angle) {
   82                         valtmp = coord.i - (coord.q >> iter);
   83                         coord.q += (coord.i >> iter);
   84                         angle += arctan_table[iter];
   85                 } else {
   86                         valtmp = coord.i + (coord.q >> iter);
   87                         coord.q -= (coord.i >> iter);
   88                         angle -= arctan_table[iter];
   89                 }
   90                 coord.i = valtmp;
   91         }
   92 
   93         coord.i *= signx;
   94         coord.q *= signx;
   95         return coord;
   96 }
   97 EXPORT_SYMBOL(cordic_calc_iq);
   98 
   99 MODULE_DESCRIPTION("CORDIC algorithm");
  100 MODULE_AUTHOR("Broadcom Corporation");
  101 MODULE_LICENSE("Dual BSD/GPL");

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FreeBSD/Linux Kernel Cross Reference sys/lib/cordic.c

FreeBSD/Linux Kernel Cross Reference
sys/lib/cordic.c