Add fixed precision atan2() function

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3834 42af7a65-404d-4744-a932-0658087f49c3

ChangeLog

@@ -1959,4 +1959,6 @@
 	  touchscreen interface.  Add a driver for the TI TSC2007 touchscreen
 	  controller.
 	* graphics/nxglib/lcd and fb:  Add low level routines to set single pixels.
+	* lib/math/lib_b16atan2.c:  Add a fixed precision atan2() function
+
 

include/fixedmath.h

@@ -217,6 +217,7 @@ EXTERN ub16_t ub16divub16(ub16_t num, ub16_t denom);
 
 EXTERN b16_t b16sin(b16_t rad);
 EXTERN b16_t b16cos(b16_t rad);
+EXTERN b16_t b16atan2(b16_t y, b16_t x);
 
 #undef EXTERN
 #if defined(__cplusplus)

lib/math/Make.defs

@@ -33,5 +33,5 @@
 #
 ############################################################################
 
-MATH_SRCS = lib_rint.c lib_fixedmath.c lib_b16sin.c lib_b16cos.c
+MATH_SRCS = lib_rint.c lib_fixedmath.c lib_b16sin.c lib_b16cos.c lib_b16atan2.c
 

lib/math/lib_b16atan2.c

@@ -0,0 +1,108 @@
+/****************************************************************************
+ * lib/math/lib_b16atan2.c
+ *
+ *   Copyright (C) 2011 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <fixedmath.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define B16_C1     0x00000373 /* 0.013480470 */
+#define B16_C2     0x00000eb7 /* 0.057477314 */
+#define B16_C3     0x00001f0a /* 0.121239071 */
+#define B16_C4     0x00003215 /* 0.195635925 */
+#define B16_C5     0x0000553f /* 0.332994597 */
+#define B16_C6     0x00010000 /* 0.999995630 */
+#define B16_HALFPI 0x00019220 /* 1.570796327 */
+#define B16_PI     0x00032440 /* 3.141592654 */
+
+#ifndef MAX
+#  define MAX(a,b) (a > b ? a : b)
+#endif
+
+#ifndef MIN
+#  define MIN(a,b) (a < b ? a : b)
+#endif
+
+#ifndef ABS
+#  define ABS(a)   (a < 0 ? -a : a)
+#endif
+
+/****************************************************************************
+ * Global Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: b16atan2
+ *
+ * Description:
+ *   atan2 calculates the arctangent of y/x.  (Based on a algorithm I saw
+ *   posted on the internet... now I have lost the link -- sorry).
+ *
+ ****************************************************************************/
+
+b16_t b16atan2(b16_t y, b16_t x)
+{
+  b16_t t0;
+  b16_t t1;
+  b16_t t2;
+  b16_t t3;
+
+  t2 = ABS(x);
+  t1 = ABS(y);
+  t0 = MAX(t2, t1);
+  t1 = MIN(t2, t1);
+  t2 = ub16inv(t0);
+  t2 = b16mulb16(t1, t2);
+
+  t3 = b16mulb16(t2, t2); 
+  t0 =                   - B16_C1;
+  t0 = b16mulb16(t0, t3) + B16_C2;
+  t0 = b16mulb16(t0, t3) - B16_C3;
+  t0 = b16mulb16(t0, t3) + B16_C4;
+  t0 = b16mulb16(t0, t3) - B16_C5;
+  t0 = b16mulb16(t0, t3) + B16_C6;
+  t2 = b16mulb16(t0, t2);
+
+  t2 = (ABS(y) > ABS(x)) ? B16_HALFPI - t2 : t2;
+  t2 = (x < 0) ?  B16_PI - t2 : t2;
+  t2 = (y < 0) ? -t2 : t2;
+
+  return t2;
+}