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//-------------------------------------------------------------------------------
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//$Header: /home/dashley/cvsrep/uculib01/uculib01/src/stm8/cosmic/modxx/atatanix100odegx1rrxx/src/atatanix100odegx1rrxx.c,v 1.4 2010/02/20 02:20:38 dashley Exp $
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//-------------------------------------------------------------------------------
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//Copyright (c)2010 David T. Ashley
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//
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//Permission is hereby granted, free of charge, to any person obtaining a copy
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//of this software source code and associated documentation files (the
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//"Software"), to deal in the Software without restriction, including without
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//limitation the rights to use, copy, modify, merge, publish, distribute,
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//sublicense, and/or sell copies of the Software, and to permit persons to whom
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//the Software is furnished to do so, subject to the following conditions:
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//
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//The above copyright notice and this permission notice shall be included in
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//all copies or substantial portions of the Software.
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//
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//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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//THE SOFTWARE.
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//-------------------------------------------------------------------------------
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#include "uculib.h"
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UCU_UINT8 UcuAtAtanIx100Odegx1RRxx(UCU_UINT16 arg)
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{
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static const UCU_UINT16 atan_lu[90] = // arctan() precision of 1 degree
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{
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//This table was generated by a C program.
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//The integers below represent the "breakpoints". For example,
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//the tangents of 48 and 49 degrees are:
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// 48 : 1.1106
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// 49 : 1.1504
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//The entry under 48 below (113) does not represent the tangent of 48
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//degrees. Rather, it represents the point at which the returned arctangent
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//should switch from 48 to 49 degrees. The table entries are approximately
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//the midpoints between arctangents of integer degrees. This allows the
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//returned arctangent to be to the closest degree.
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//
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/* 0 degrees */ 0, 2, 4, 6, 7,
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/* 5 degrees */ 9, 11, 13, 14, 16,
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/* 10 degrees */ 18, 20, 22, 24, 25,
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/* 15 degrees */ 27, 29, 31, 33, 35,
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/* 20 degrees */ 37, 39, 41, 43, 45,
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/* 25 degrees */ 47, 49, 52, 54, 56,
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/* 30 degrees */ 58, 61, 63, 66, 68,
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/* 35 degrees */ 71, 73, 76, 79, 82,
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/* 40 degrees */ 85, 88, 91, 94, 98,
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/* 45 degrees */ 101, 105, 109, 113, 117,
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/* 50 degrees */ 121, 125, 130, 135, 140,
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/* 55 degrees */ 145, 151, 156, 163, 169,
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/* 60 degrees */ 176, 184, 192, 200, 209,
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/* 65 degrees */ 219, 229, 241, 253, 267,
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/* 70 degrees */ 282, 298, 317, 337, 360,
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/* 75 degrees */ 386, 416, 451, 491, 539,
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/* 80 degrees */ 597, 669, 759, 877, 1038,
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/* 85 degrees */ 1270, 1634, 2290, 3818, 11458
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};
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UCU_UINT8 bottom, top, middle;
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bottom = 0;
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top = 90; //Note: element [90] in the lookup table
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//isn't actually necessary. If 90 is the eventual
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//return value, bottom converges to top and top
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//remains unchanged.
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//
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//Once (bottom == top), no more dereferencing is done.
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//This was verified both by hand analysis and by running
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//the program on a *nix platform.
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//This algorithm is a modified classic binary search.
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//
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while (bottom != top)
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{
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middle = bottom + top;
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middle >>= 1;
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if (atan_lu[middle] >= arg)
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{
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//The "middle" table entry is at least as large as the argument.
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//We are clear to lower the ceiling to be the middle.
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//
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top = middle;
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}
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else
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{
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//The "middle" entry is less than the argument. That automatically
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//makes the middle unsuitable, so the correct return value has
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//to be at least one larger than the middle.
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//
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bottom = middle + 1;
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}
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}
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return(bottom);
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}
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//-------------------------------------------------------------------------------
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//End of $Id: atatanix100odegx1rrxx.c,v 1.4 2010/02/20 02:20:38 dashley Exp $
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//-------------------------------------------------------------------------------
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//$Log: atatanix100odegx1rrxx.c,v $
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//Revision 1.4 2010/02/20 02:20:38 dashley
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//Comments removed.
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//
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//Revision 1.3 2010/01/31 00:14:00 dashley
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//Renaming/addition of arctangent function.
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//
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//Revision 1.2 2010/01/22 03:15:29 dashley
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//Extra line removed.
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//
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//Revision 1.1 2010/01/22 03:14:47 dashley
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//Initial checkin.
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//-------------------------------------------------------------------------------
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