src/main/drivers/sdcard_standard.c

   1 /*
   2  * This file is part of Cleanflight and Betaflight.
   3  *
   4  * Cleanflight and Betaflight are free software. You can redistribute
   5  * this software and/or modify this software under the terms of the
   6  * GNU General Public License as published by the Free Software
   7  * Foundation, either version 3 of the License, or (at your option)
   8  * any later version.
   9  *
  10  * Cleanflight and Betaflight are distributed in the hope that they
  11  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  12  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  13  * See the GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this software.
  17  *
  18  * If not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <stdint.h>
  22
  23 #include "platform.h"
  24
  25 #include "sdcard_standard.h"
  26 #include "common/maths.h"
  27
  28 /**
  29  * Read a bitfield from an array of bits (the bit at index 0 being the most-significant bit of the first byte in
  30  * the buffer).
  31  */
  32 uint32_t readBitfield(uint8_t *buffer, unsigned bitIndex, unsigned bitLen)
  33 {
  34     uint32_t result = 0;
  35     unsigned bitInByteOffset = bitIndex % 8;
  36     uint8_t bufferByte;
  37
  38     buffer += bitIndex / 8;
  39
  40     // Align the bitfield to be read to the top of the buffer
  41     bufferByte = *buffer << bitInByteOffset;
  42
  43     while (bitLen > 0) {
  44         unsigned bitsThisLoop = MIN(8 - bitInByteOffset, bitLen);
  45
  46         result = (result << bitsThisLoop) | (bufferByte >> (8 - bitsThisLoop));
  47
  48         buffer++;
  49         bufferByte = *buffer;
  50
  51         bitLen -= bitsThisLoop;
  52         bitInByteOffset = 0;
  53     }
  54
  55     return result;
  56 }