1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
#ifndef __BITFIELD_H__
#define __BITFIELD_H__
#include <stdint.h>
#include <stdbool.h>
/* Public: Reads a subset of bits from a byte array.
*
* data - the bytes in question.
* startPos - the starting index of the bit field (beginning from 0).
* numBits - the width of the bit field to extract.
* bigEndian - if the data passed in is little endian, set this to false and it
* will be flipped before grabbing the bit field.
*
* Bit fields are positioned according to big-endian bit layout, but inside the
* bit field, values are represented as little-endian. Therefore, to get the bit
* field, we swap the overall byte order if bigEndian == false and
* use the value we find in the field (assuming the embedded platform is little
* endian).
*
* For example, the bit layout of the value "42" (i.e. 00101010 set at position
* 14 with length 6 is:
*
* 000000000000001010100000000000000000000000000000000000000000000
*
* and the same value and position but with length 8 is:
*
* 000000000000000010101000000000000000000000000000000000000000000
*
* If the architecture where is code is running is little-endian, the input data
* will be swapped before grabbing the bit field.
*
* Examples
*
* uint64_t value = getBitField(data, 2, 4);
*
* Returns the value of the requested bit field.
*/
uint64_t getBitField(uint64_t data, int startPos, int numBits, bool bigEndian);
/* Public: Set the bit field in the given data array to the new value.
*
* data - a byte array with size at least startPos + numBits.
* value - the value to set in the bit field.
* startPos - the starting index of the bit field (beginning from 0).
*/
void setBitField(uint64_t* data, uint64_t value, int startPos, int numBits);
/* Public: Retreive the nth byte out of 8 bytes in a uint64_t.
*
* source - the source data to retreive the byte from.
* byteNum - the index of the byte, starting at 0 and assuming big-endian order.
*
* Returns the requested byte from the source bytes.
*/
uint8_t nthByte(uint64_t source, int byteNum);
#endif // __BITFIELD_H__
|
