LXR linux/lib/cordic.c

   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
  28static 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 */
  55struct 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}
  97EXPORT_SYMBOL(cordic_calc_iq);
  98
  99MODULE_DESCRIPTION("CORDIC algorithm");
 100MODULE_AUTHOR("Broadcom Corporation");
 101MODULE_LICENSE("Dual BSD/GPL");
 102