/* | |

* dvb-math provides some complex fixed-point math | |

* operations shared between the dvb related stuff | |

* | |

* Copyright (C) 2006 Christoph Pfister (christophpfister@gmail.com) | |

* | |

* This library is free software; you can redistribute it and/or modify | |

* it under the terms of the GNU Lesser General Public License as | |

* published by the Free Software Foundation; either version 2.1 of | |

* the License, or (at your option) any later version. | |

* | |

* This program is distributed in the hope that it will be useful, | |

* but WITHOUT ANY WARRANTY; without even the implied warranty of | |

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |

* GNU Lesser General Public License for more details. | |

* | |

* You should have received a copy of the GNU Lesser General Public | |

* License along with this library; if not, write to the Free Software | |

* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |

*/ | |

#include <linux/bitops.h> | |

#include <linux/kernel.h> | |

#include <linux/module.h> | |

#include <asm/bug.h> | |

#include "dvb_math.h" | |

static const unsigned short logtable[256] = { | |

0x0000, 0x0171, 0x02e0, 0x044e, 0x05ba, 0x0725, 0x088e, 0x09f7, | |

0x0b5d, 0x0cc3, 0x0e27, 0x0f8a, 0x10eb, 0x124b, 0x13aa, 0x1508, | |

0x1664, 0x17bf, 0x1919, 0x1a71, 0x1bc8, 0x1d1e, 0x1e73, 0x1fc6, | |

0x2119, 0x226a, 0x23ba, 0x2508, 0x2656, 0x27a2, 0x28ed, 0x2a37, | |

0x2b80, 0x2cc8, 0x2e0f, 0x2f54, 0x3098, 0x31dc, 0x331e, 0x345f, | |

0x359f, 0x36de, 0x381b, 0x3958, 0x3a94, 0x3bce, 0x3d08, 0x3e41, | |

0x3f78, 0x40af, 0x41e4, 0x4319, 0x444c, 0x457f, 0x46b0, 0x47e1, | |

0x4910, 0x4a3f, 0x4b6c, 0x4c99, 0x4dc5, 0x4eef, 0x5019, 0x5142, | |

0x526a, 0x5391, 0x54b7, 0x55dc, 0x5700, 0x5824, 0x5946, 0x5a68, | |

0x5b89, 0x5ca8, 0x5dc7, 0x5ee5, 0x6003, 0x611f, 0x623a, 0x6355, | |

0x646f, 0x6588, 0x66a0, 0x67b7, 0x68ce, 0x69e4, 0x6af8, 0x6c0c, | |

0x6d20, 0x6e32, 0x6f44, 0x7055, 0x7165, 0x7274, 0x7383, 0x7490, | |

0x759d, 0x76aa, 0x77b5, 0x78c0, 0x79ca, 0x7ad3, 0x7bdb, 0x7ce3, | |

0x7dea, 0x7ef0, 0x7ff6, 0x80fb, 0x81ff, 0x8302, 0x8405, 0x8507, | |

0x8608, 0x8709, 0x8809, 0x8908, 0x8a06, 0x8b04, 0x8c01, 0x8cfe, | |

0x8dfa, 0x8ef5, 0x8fef, 0x90e9, 0x91e2, 0x92db, 0x93d2, 0x94ca, | |

0x95c0, 0x96b6, 0x97ab, 0x98a0, 0x9994, 0x9a87, 0x9b7a, 0x9c6c, | |

0x9d5e, 0x9e4f, 0x9f3f, 0xa02e, 0xa11e, 0xa20c, 0xa2fa, 0xa3e7, | |

0xa4d4, 0xa5c0, 0xa6ab, 0xa796, 0xa881, 0xa96a, 0xaa53, 0xab3c, | |

0xac24, 0xad0c, 0xadf2, 0xaed9, 0xafbe, 0xb0a4, 0xb188, 0xb26c, | |

0xb350, 0xb433, 0xb515, 0xb5f7, 0xb6d9, 0xb7ba, 0xb89a, 0xb97a, | |

0xba59, 0xbb38, 0xbc16, 0xbcf4, 0xbdd1, 0xbead, 0xbf8a, 0xc065, | |

0xc140, 0xc21b, 0xc2f5, 0xc3cf, 0xc4a8, 0xc580, 0xc658, 0xc730, | |

0xc807, 0xc8de, 0xc9b4, 0xca8a, 0xcb5f, 0xcc34, 0xcd08, 0xcddc, | |

0xceaf, 0xcf82, 0xd054, 0xd126, 0xd1f7, 0xd2c8, 0xd399, 0xd469, | |

0xd538, 0xd607, 0xd6d6, 0xd7a4, 0xd872, 0xd93f, 0xda0c, 0xdad9, | |

0xdba5, 0xdc70, 0xdd3b, 0xde06, 0xded0, 0xdf9a, 0xe063, 0xe12c, | |

0xe1f5, 0xe2bd, 0xe385, 0xe44c, 0xe513, 0xe5d9, 0xe69f, 0xe765, | |

0xe82a, 0xe8ef, 0xe9b3, 0xea77, 0xeb3b, 0xebfe, 0xecc1, 0xed83, | |

0xee45, 0xef06, 0xefc8, 0xf088, 0xf149, 0xf209, 0xf2c8, 0xf387, | |

0xf446, 0xf505, 0xf5c3, 0xf680, 0xf73e, 0xf7fb, 0xf8b7, 0xf973, | |

0xfa2f, 0xfaea, 0xfba5, 0xfc60, 0xfd1a, 0xfdd4, 0xfe8e, 0xff47 | |

}; | |

unsigned int intlog2(u32 value) | |

{ | |

/** | |

* returns: log2(value) * 2^24 | |

* wrong result if value = 0 (log2(0) is undefined) | |

*/ | |

unsigned int msb; | |

unsigned int logentry; | |

unsigned int significand; | |

unsigned int interpolation; | |

if (unlikely(value == 0)) { | |

WARN_ON(1); | |

return 0; | |

} | |

/* first detect the msb (count begins at 0) */ | |

msb = fls(value) - 1; | |

/** | |

* now we use a logtable after the following method: | |

* | |

* log2(2^x * y) * 2^24 = x * 2^24 + log2(y) * 2^24 | |

* where x = msb and therefore 1 <= y < 2 | |

* first y is determined by shifting the value left | |

* so that msb is bit 31 | |

* 0x00231f56 -> 0x8C7D5800 | |

* the result is y * 2^31 -> "significand" | |

* then the highest 9 bits are used for a table lookup | |

* the highest bit is discarded because it's always set | |

* the highest nine bits in our example are 100011000 | |

* so we would use the entry 0x18 | |

*/ | |

significand = value << (31 - msb); | |

logentry = (significand >> 23) & 0xff; | |

/** | |

* last step we do is interpolation because of the | |

* limitations of the log table the error is that part of | |

* the significand which isn't used for lookup then we | |

* compute the ratio between the error and the next table entry | |

* and interpolate it between the log table entry used and the | |

* next one the biggest error possible is 0x7fffff | |

* (in our example it's 0x7D5800) | |

* needed value for next table entry is 0x800000 | |

* so the interpolation is | |

* (error / 0x800000) * (logtable_next - logtable_current) | |

* in the implementation the division is moved to the end for | |

* better accuracy there is also an overflow correction if | |

* logtable_next is 256 | |

*/ | |

interpolation = ((significand & 0x7fffff) * | |

((logtable[(logentry + 1) & 0xff] - | |

logtable[logentry]) & 0xffff)) >> 15; | |

/* now we return the result */ | |

return ((msb << 24) + (logtable[logentry] << 8) + interpolation); | |

} | |

EXPORT_SYMBOL(intlog2); | |

unsigned int intlog10(u32 value) | |

{ | |

/** | |

* returns: log10(value) * 2^24 | |

* wrong result if value = 0 (log10(0) is undefined) | |

*/ | |

u64 log; | |

if (unlikely(value == 0)) { | |

WARN_ON(1); | |

return 0; | |

} | |

log = intlog2(value); | |

/** | |

* we use the following method: | |

* log10(x) = log2(x) * log10(2) | |

*/ | |

return (log * 646456993) >> 31; | |

} | |

EXPORT_SYMBOL(intlog10); |