common/util.c

   1 /*
   2 Copyright 2011 Jun Wako <wakojun@gmail.com>
   3
   4 This program is free software: you can redistribute it and/or modify
   5 it under the terms of the GNU General Public License as published by
   6 the Free Software Foundation, either version 2 of the License, or
   7 (at your option) any later version.
   8
   9 This program is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 GNU General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  16 */
  17
  18 #include "util.h"
  19
  20 // bit population - return number of on-bit
  21 uint8_t bitpop(uint8_t bits)
  22 {
  23     uint8_t c;
  24     for (c = 0; bits; c++)
  25         bits &= bits -1;
  26     return c;
  27 /*
  28     const uint8_t bit_count[] = { 0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4 };
  29     return bit_count[bits>>4] + bit_count[bits&0x0F]
  30 */
  31 }
  32
  33 // most significant on-bit - return highest location of on-bit
  34 uint8_t biton(uint8_t bits)
  35 {
  36     uint8_t n = 0;
  37     if (bits >> 4) { bits >>= 4; n += 4;}
  38     if (bits >> 2) { bits >>= 2; n += 2;}
  39     if (bits >> 1) { bits >>= 1; n += 1;}
  40     return n;
  41 }