146 lines
5.3 KiB
C
146 lines
5.3 KiB
C
/*
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* dvb-math provides some complex fixed-point math
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* operations shared between the dvb related stuff
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*
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* Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com)
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation; either version 2.1 of
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* the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/bitops.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <asm/bug.h>
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#include "dvb_math.h"
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static const unsigned short logtable[256] = {
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0x0000, 0x0171, 0x02e0, 0x044e, 0x05ba, 0x0725, 0x088e, 0x09f7,
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0x0b5d, 0x0cc3, 0x0e27, 0x0f8a, 0x10eb, 0x124b, 0x13aa, 0x1508,
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0x1664, 0x17bf, 0x1919, 0x1a71, 0x1bc8, 0x1d1e, 0x1e73, 0x1fc6,
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0x2119, 0x226a, 0x23ba, 0x2508, 0x2656, 0x27a2, 0x28ed, 0x2a37,
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0x2b80, 0x2cc8, 0x2e0f, 0x2f54, 0x3098, 0x31dc, 0x331e, 0x345f,
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0x359f, 0x36de, 0x381b, 0x3958, 0x3a94, 0x3bce, 0x3d08, 0x3e41,
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0x3f78, 0x40af, 0x41e4, 0x4319, 0x444c, 0x457f, 0x46b0, 0x47e1,
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0x4910, 0x4a3f, 0x4b6c, 0x4c99, 0x4dc5, 0x4eef, 0x5019, 0x5142,
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0x526a, 0x5391, 0x54b7, 0x55dc, 0x5700, 0x5824, 0x5946, 0x5a68,
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0x5b89, 0x5ca8, 0x5dc7, 0x5ee5, 0x6003, 0x611f, 0x623a, 0x6355,
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0x646f, 0x6588, 0x66a0, 0x67b7, 0x68ce, 0x69e4, 0x6af8, 0x6c0c,
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0x6d20, 0x6e32, 0x6f44, 0x7055, 0x7165, 0x7274, 0x7383, 0x7490,
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0x759d, 0x76aa, 0x77b5, 0x78c0, 0x79ca, 0x7ad3, 0x7bdb, 0x7ce3,
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0x7dea, 0x7ef0, 0x7ff6, 0x80fb, 0x81ff, 0x8302, 0x8405, 0x8507,
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0x8608, 0x8709, 0x8809, 0x8908, 0x8a06, 0x8b04, 0x8c01, 0x8cfe,
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0x8dfa, 0x8ef5, 0x8fef, 0x90e9, 0x91e2, 0x92db, 0x93d2, 0x94ca,
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0x95c0, 0x96b6, 0x97ab, 0x98a0, 0x9994, 0x9a87, 0x9b7a, 0x9c6c,
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0x9d5e, 0x9e4f, 0x9f3f, 0xa02e, 0xa11e, 0xa20c, 0xa2fa, 0xa3e7,
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0xa4d4, 0xa5c0, 0xa6ab, 0xa796, 0xa881, 0xa96a, 0xaa53, 0xab3c,
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0xac24, 0xad0c, 0xadf2, 0xaed9, 0xafbe, 0xb0a4, 0xb188, 0xb26c,
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0xb350, 0xb433, 0xb515, 0xb5f7, 0xb6d9, 0xb7ba, 0xb89a, 0xb97a,
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0xba59, 0xbb38, 0xbc16, 0xbcf4, 0xbdd1, 0xbead, 0xbf8a, 0xc065,
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0xc140, 0xc21b, 0xc2f5, 0xc3cf, 0xc4a8, 0xc580, 0xc658, 0xc730,
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0xc807, 0xc8de, 0xc9b4, 0xca8a, 0xcb5f, 0xcc34, 0xcd08, 0xcddc,
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0xceaf, 0xcf82, 0xd054, 0xd126, 0xd1f7, 0xd2c8, 0xd399, 0xd469,
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0xd538, 0xd607, 0xd6d6, 0xd7a4, 0xd872, 0xd93f, 0xda0c, 0xdad9,
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0xdba5, 0xdc70, 0xdd3b, 0xde06, 0xded0, 0xdf9a, 0xe063, 0xe12c,
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0xe1f5, 0xe2bd, 0xe385, 0xe44c, 0xe513, 0xe5d9, 0xe69f, 0xe765,
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0xe82a, 0xe8ef, 0xe9b3, 0xea77, 0xeb3b, 0xebfe, 0xecc1, 0xed83,
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0xee45, 0xef06, 0xefc8, 0xf088, 0xf149, 0xf209, 0xf2c8, 0xf387,
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0xf446, 0xf505, 0xf5c3, 0xf680, 0xf73e, 0xf7fb, 0xf8b7, 0xf973,
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0xfa2f, 0xfaea, 0xfba5, 0xfc60, 0xfd1a, 0xfdd4, 0xfe8e, 0xff47
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};
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unsigned int intlog2(u32 value)
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{
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/**
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* returns: log2(value) * 2^24
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* wrong result if value = 0 (log2(0) is undefined)
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*/
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unsigned int msb;
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unsigned int logentry;
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unsigned int significand;
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unsigned int interpolation;
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if (unlikely(value == 0)) {
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WARN_ON(1);
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return 0;
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}
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/* first detect the msb (count begins at 0) */
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msb = fls(value) - 1;
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/**
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* now we use a logtable after the following method:
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*
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* log2(2^x * y) * 2^24 = x * 2^24 + log2(y) * 2^24
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* where x = msb and therefore 1 <= y < 2
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* first y is determined by shifting the value left
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* so that msb is bit 31
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* 0x00231f56 -> 0x8C7D5800
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* the result is y * 2^31 -> "significand"
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* then the highest 9 bits are used for a table lookup
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* the highest bit is discarded because it's always set
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* the highest nine bits in our example are 100011000
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* so we would use the entry 0x18
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*/
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significand = value << (31 - msb);
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logentry = (significand >> 23) & 0xff;
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/**
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* last step we do is interpolation because of the
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* limitations of the log table the error is that part of
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* the significand which isn't used for lookup then we
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* compute the ratio between the error and the next table entry
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* and interpolate it between the log table entry used and the
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* next one the biggest error possible is 0x7fffff
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* (in our example it's 0x7D5800)
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* needed value for next table entry is 0x800000
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* so the interpolation is
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* (error / 0x800000) * (logtable_next - logtable_current)
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* in the implementation the division is moved to the end for
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* better accuracy there is also an overflow correction if
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* logtable_next is 256
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*/
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interpolation = ((significand & 0x7fffff) *
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((logtable[(logentry + 1) & 0xff] -
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logtable[logentry]) & 0xffff)) >> 15;
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/* now we return the result */
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return ((msb << 24) + (logtable[logentry] << 8) + interpolation);
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}
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EXPORT_SYMBOL(intlog2);
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unsigned int intlog10(u32 value)
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{
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/**
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* returns: log10(value) * 2^24
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* wrong result if value = 0 (log10(0) is undefined)
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*/
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u64 log;
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if (unlikely(value == 0)) {
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WARN_ON(1);
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return 0;
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}
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log = intlog2(value);
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/**
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* we use the following method:
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* log10(x) = log2(x) * log10(2)
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*/
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return (log * 646456993) >> 31;
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}
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EXPORT_SYMBOL(intlog10);
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