radio/src/maths.cpp

   1 /*
   2  * Copyright (C) OpenTX
   3  *
   4  * Based on code named
   5  *   th9x - http://code.google.com/p/th9x
   6  *   er9x - http://code.google.com/p/er9x
   7  *   gruvin9x - http://code.google.com/p/gruvin9x
   8  *
   9  * License GPLv2: http://www.gnu.org/licenses/gpl-2.0.html
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License version 2 as
  13  * published by the Free Software Foundation.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18  * GNU General Public License for more details.
  19  */
  20
  21 #include "opentx.h"
  22
  23 uint16_t isqrt32(uint32_t n)
  24 {
  25   uint16_t c = 0x8000;
  26   uint16_t g = 0x8000;
  27
  28   for (;;) {
  29     if ((uint32_t)g*g > n)
  30       g ^= c;
  31     c >>= 1;
  32     if(c == 0)
  33       return g;
  34     g |= c;
  35   }
  36 }
  37
  38 /*
  39   Division by 10 and rounding or fixed point arithmetic values
  40
  41   Examples:
  42     value -> result
  43     105 ->  11
  44     104 ->  10
  45    -205 -> -21
  46    -204 -> -20
  47 */
  48
  49
  50 // djb2 hash algorithm
  51 uint32_t hash(const void * ptr, uint32_t size)
  52 {
  53   const uint8_t * data = (const uint8_t *)ptr;
  54   uint32_t hash = 5381;
  55   for (uint32_t i=0; i<size; i++) {
  56     hash = ((hash << 5) + hash) + data[i]; /* hash * 33 + c */
  57   }
  58   return hash;
  59 }