From f98fd72fe7d1076cf7a7758a60541a65d5fda578 Mon Sep 17 00:00:00 2001
From: Jens Arnold <amiconn@rockbox.org>
Date: Sun, 10 Dec 2006 22:50:00 +0000
Subject: [PATCH] Beginnings of a fixed point math library for use in plugins.
 fsincos() only for now, mostly copied from eq.c

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@11709 a1c6a512-1295-4272-9138-f99709370657
---
 apps/plugins/lib/fixedpoint.c | 119 ++++++++++++++++++++++++++++++++++
 apps/plugins/lib/fixedpoint.h |  22 +++++++
 2 files changed, 141 insertions(+)
 create mode 100755 apps/plugins/lib/fixedpoint.c
 create mode 100755 apps/plugins/lib/fixedpoint.h

diff --git a/apps/plugins/lib/fixedpoint.c b/apps/plugins/lib/fixedpoint.c
new file mode 100755
index 0000000000..914bc8c02a
--- /dev/null
+++ b/apps/plugins/lib/fixedpoint.c
@@ -0,0 +1,119 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2006 Jens Arnold
+ *
+ * Fixed point library for plugins
+ *
+ * All files in this archive are subject to the GNU General Public License.
+ * See the file COPYING in the source tree root for full license agreement.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+#include <inttypes.h>
+
+/* Inverse gain of circular cordic rotation in s0.31 format. */
+static const long cordic_circular_gain = 0xb2458939; /* 0.607252929 */
+
+/* Table of values of atan(2^-i) in 0.32 format fractions of pi where pi = 0xffffffff / 2 */
+static const unsigned long atan_table[] = {
+    0x1fffffff, /* +0.785398163 (or pi/4) */
+    0x12e4051d, /* +0.463647609 */
+    0x09fb385b, /* +0.244978663 */
+    0x051111d4, /* +0.124354995 */
+    0x028b0d43, /* +0.062418810 */
+    0x0145d7e1, /* +0.031239833 */
+    0x00a2f61e, /* +0.015623729 */
+    0x00517c55, /* +0.007812341 */
+    0x0028be53, /* +0.003906230 */
+    0x00145f2e, /* +0.001953123 */
+    0x000a2f98, /* +0.000976562 */
+    0x000517cc, /* +0.000488281 */
+    0x00028be6, /* +0.000244141 */
+    0x000145f3, /* +0.000122070 */
+    0x0000a2f9, /* +0.000061035 */
+    0x0000517c, /* +0.000030518 */
+    0x000028be, /* +0.000015259 */
+    0x0000145f, /* +0.000007629 */
+    0x00000a2f, /* +0.000003815 */
+    0x00000517, /* +0.000001907 */
+    0x0000028b, /* +0.000000954 */
+    0x00000145, /* +0.000000477 */
+    0x000000a2, /* +0.000000238 */
+    0x00000051, /* +0.000000119 */
+    0x00000028, /* +0.000000060 */
+    0x00000014, /* +0.000000030 */
+    0x0000000a, /* +0.000000015 */
+    0x00000005, /* +0.000000007 */
+    0x00000002, /* +0.000000004 */
+    0x00000001, /* +0.000000002 */
+    0x00000000, /* +0.000000001 */
+    0x00000000, /* +0.000000000 */
+};
+
+/**
+ * Implements sin and cos using CORDIC rotation.
+ *
+ * @param phase has range from 0 to 0xffffffff, representing 0 and
+ *        2*pi respectively.
+ * @param cos return address for cos
+ * @return sin of phase, value is a signed value from LONG_MIN to LONG_MAX,
+ *         representing -1 and 1 respectively. 
+ */
+long fsincos(unsigned long phase, long *cos) 
+{
+    int32_t x, x1, y, y1;
+    unsigned long z, z1;
+    int i;
+
+    /* Setup initial vector */
+    x = cordic_circular_gain;
+    y = 0;
+    z = phase;
+
+    /* The phase has to be somewhere between 0..pi for this to work right */
+    if (z < 0xffffffff / 4) {
+        /* z in first quadrant, z += pi/2 to correct */
+        x = -x;
+        z += 0xffffffff / 4;
+    } else if (z < 3 * (0xffffffff / 4)) {
+        /* z in third quadrant, z -= pi/2 to correct */
+        z -= 0xffffffff / 4;
+    } else {
+        /* z in fourth quadrant, z -= 3pi/2 to correct */
+        x = -x;
+        z -= 3 * (0xffffffff / 4);
+    }
+
+    /* Each iteration adds roughly 1-bit of extra precision */
+    for (i = 0; i < 31; i++) {
+        x1 = x >> i;
+        y1 = y >> i;
+        z1 = atan_table[i];
+
+        /* Decided which direction to rotate vector. Pivot point is pi/2 */
+        if (z >= 0xffffffff / 4) {
+            x -= y1;
+            y += x1;
+            z -= z1;
+        } else {
+            x += y1;
+            y -= x1;
+            z += z1;
+        }
+    }
+
+    if (cos)
+        *cos = x;
+
+    return y;
+}
diff --git a/apps/plugins/lib/fixedpoint.h b/apps/plugins/lib/fixedpoint.h
new file mode 100755
index 0000000000..065f9fbb43
--- /dev/null
+++ b/apps/plugins/lib/fixedpoint.h
@@ -0,0 +1,22 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2006 Jens Arnold
+ *
+ * Fixed point library for plugins
+ *
+ * All files in this archive are subject to the GNU General Public License.
+ * See the file COPYING in the source tree root for full license agreement.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+
+long fsincos(unsigned long phase, long *cos);