lib: cordic: add library module providing cordic angle calculation

The brcm80211 driver in the staging tree has a cordic function to
determine cosine and sine for a given angle. Feedback received from
John Linville suggested that these kind of functions should be made
available to others as a library function in the kernel tree. The
b43 driver also has a cordic angle calculation implemented.

Cc: linux-kernel@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Larry Finger <Larry.Finger@lwfinger.net>
Reviewed-by: Roland Vossen <rvossen@broadcom.com>
Reviewed-by: Henry Ptasinski <henryp@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

4 files changed, 158 insertions, 0 deletions

diff --git a/include/linux/cordic.h b/include/linux/cordic.h
new file mode 100644
index 000000000000..f932093e20c2
--- /dev/null
+++ b/include/linux/cordic.h
@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2011 Broadcom Corporation
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#ifndef __CORDIC_H_
+#define __CORDIC_H_
+
+#include <linux/types.h>
+
+/**
+ * struct cordic_iq - i/q coordinate.
+ *
+ * @i: real part of coordinate (in phase).
+ * @q: imaginary part of coordinate (quadrature).
+ */
+struct cordic_iq {
+        s32 i;
+        s32 q;
+};
+
+/**
+ * cordic_calc_iq() - calculates the i/q coordinate for given angle.
+ *
+ * @theta: angle in degrees for which i/q coordinate is to be calculated.
+ * @coord: function output parameter holding the i/q coordinate.
+ *
+ * The function calculates the i/q coordinate for a given angle using
+ * cordic algorithm. The coordinate consists of a real (i) and an
+ * imaginary (q) part. The real part is essentially the cosine of the
+ * angle and the imaginary part is the sine of the angle. The returned
+ * values are scaled by 2^16 for precision. The range for theta is
+ * for -180 degrees to +180 degrees. Passed values outside this range are
+ * converted before doing the actual calculation.
+ */
+struct cordic_iq cordic_calc_iq(s32 theta);
+
+#endif /* __CORDIC_H_ */
diff --git a/lib/Kconfig b/lib/Kconfig
index ff9e5a34be76..5c702047c57f 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -279,4 +279,11 @@ config AVERAGE
 
           If unsure, say N.
 
+config CORDIC
+        tristate "Cordic function"
+        help
+          The option provides arithmetic function using cordic algorithm
+          so its calculations are in fixed point. Modules can select this
+          when they require this function. Module will be called cordic.
+
 endmenu
diff --git a/lib/Makefile b/lib/Makefile
index 704959d2018b..9e3c1b0652d1 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -117,6 +117,8 @@ obj-$(CONFIG_AVERAGE) += average.o
 
 obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o
 
+obj-$(CONFIG_CORDIC) += cordic.o
+
 hostprogs-y     := gen_crc32table
 clean-files     := crc32table.h
 
diff --git a/lib/cordic.c b/lib/cordic.c
new file mode 100644
index 000000000000..aa27a88d7e04
--- /dev/null
+++ b/lib/cordic.c
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2011 Broadcom Corporation
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+#include <linux/module.h>
+#include <linux/cordic.h>
+
+#define CORDIC_ANGLE_GEN        39797
+#define CORDIC_PRECISION_SHIFT  16
+#define CORDIC_NUM_ITER         (CORDIC_PRECISION_SHIFT + 2)
+
+#define FIXED(X)        ((s32)((X) << CORDIC_PRECISION_SHIFT))
+#define FLOAT(X)        (((X) >= 0) \
+                ? ((((X) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1) \
+                : -((((-(X)) >> (CORDIC_PRECISION_SHIFT - 1)) + 1) >> 1))
+
+static const s32 arctan_table[] = {
+        2949120,
+        1740967,
+        919879,
+        466945,
+        234379,
+        117304,
+        58666,
+        29335,
+        14668,
+        7334,
+        3667,
+        1833,
+        917,
+        458,
+        229,
+        115,
+        57,
+        29
+};
+
+/*
+ * cordic_calc_iq() - calculates the i/q coordinate for given angle
+ *
+ * theta: angle in degrees for which i/q coordinate is to be calculated
+ * coord: function output parameter holding the i/q coordinate
+ */
+struct cordic_iq cordic_calc_iq(s32 theta)
+{
+        struct cordic_iq coord;
+        s32 angle, valtmp;
+        unsigned iter;
+        int signx = 1;
+        int signtheta;
+
+        coord.i = CORDIC_ANGLE_GEN;
+        coord.q = 0;
+        angle = 0;
+
+        theta = FIXED(theta);
+        signtheta = (theta < 0) ? -1 : 1;
+        theta = ((theta + FIXED(180) * signtheta) % FIXED(360)) -
+                FIXED(180) * signtheta;
+
+        if (FLOAT(theta) > 90) {
+                theta -= FIXED(180);
+                signx = -1;
+        } else if (FLOAT(theta) < -90) {
+                theta += FIXED(180);
+                signx = -1;
+        }
+
+        for (iter = 0; iter < CORDIC_NUM_ITER; iter++) {
+                if (theta > angle) {
+                        valtmp = coord.i - (coord.q >> iter);
+                        coord.q += (coord.i >> iter);
+                        angle += arctan_table[iter];
+                } else {
+                        valtmp = coord.i + (coord.q >> iter);
+                        coord.q -= (coord.i >> iter);
+                        angle -= arctan_table[iter];
+                }
+                coord.i = valtmp;
+        }
+
+        coord.i *= signx;
+        coord.q *= signx;
+        return coord;
+}
+EXPORT_SYMBOL(cordic_calc_iq);
+
+MODULE_DESCRIPTION("Cordic functions");
+MODULE_AUTHOR("Broadcom Corporation");
+MODULE_LICENSE("Dual BSD/GPL");