[PATCH 2/2] lib: cordic: add library module providing cordicangle calculation

[Arend van Spriel]

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.

V1:
- code taken from brcm80211 driver and added kernel-doc comments.
- code compiled and tested for x86 architecture using brcm80211 driver.
- code compiled for x86_64, ARM, and MIPS architectures.

V2:
- fixed code based on comments from Randy Dunlap and Larry Finger.

Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-wireless@xxxxxxxxxxxxxxx
Cc: "John W. Linville" <linville@xxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxx>
Cc: Dan Carpenter <error27@xxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxx>
Cc: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
Reviewed-by: Roland Vossen <rvossen@xxxxxxxxxxxx>
Reviewed-by: Henry Ptasinski <henryp@xxxxxxxxxxxx>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@xxxxxxxxxxxx>
Signed-off-by: Arend van Spriel <arend@xxxxxxxxxxxx>
---
 include/linux/cordic.h                             |   48 +++++++++
 lib/Kconfig                                        |    7 ++
 lib/Makefile                                       |    2 +
 lib/cordic.c                                       |  101 ++++++++++++++++++++
 4 files changed, 158 insertions(+), 0 deletions(-)
 create mode 100644 include/linux/cordic.h
 create mode 100644 lib/cordic.c

diff --git a/include/linux/cordic.h b/include/linux/cordic.h
new file mode 100644
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 ff9e5a3..5c70204 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 704959d..9e3c1b0 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 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");
-- 
1.7.4.1


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