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>

diff --git a/include/linux/cordic.h b/include/linux/cordic.h
new file mode 100644 (file)
index 0000000..f932093
--- /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 ff9e5a34be76a2a532e2a0bde0b6da3a58c8b62c..5c702047c57ff47420f8bd11d0fc269f1e531a60 100644 (file)
--- 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 704959d2018bd69f15a6e75d56c40525d8ef3e82..9e3c1b0652d1cc51e60d951d56a832e92378ec2f 100644 (file)
--- 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 (file)
index 0000000..aa27a88
--- /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");