Kuvée / COBS

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Dependents:   Nucleo_cobs_test

COBS.cpp@0:736db4334c89, 2015-02-10 (annotated)

Committer:
glansberry
Date:
Tue Feb 10 02:29:49 2015 +0000
Revision:
0:736db4334c89
Child:
1:2b84a7482df6
COBS encoding, initial commit

Who changed what in which revision?

UserRevisionLine numberNew contents of line
glansberry 0:736db4334c89 1 /* Consistent Overhead Byte Stuffing (COBS)
glansberry 0:736db4334c89 2 by Stuart Cheshire and Mary Baker
glansberry 0:736db4334c89 3
glansberry 0:736db4334c89 4 reference: http://conferences.sigcomm.org/sigcomm/1997/papers/p062.pdf
glansberry 0:736db4334c89 5
glansberry 0:736db4334c89 6
glansberry 0:736db4334c89 7 COBS is a byte stuffing algorithm that encodes data bytes into a sequence that is easily
glansberry 0:736db4334c89 8 decoded, but simple to identify when blocks of data start. The idea is elegant. The sequence starts with
glansberry 0:736db4334c89 9 a zero, followed by the number of bytes until the next zero, in that location is the number of bytes again, etc.
glansberry 0:736db4334c89 10 To keep a data stream synchronized, all one must do is watch for the zeros, which will never occur except when
glansberry 0:736db4334c89 11 a new byte sequence is starting.
glansberry 0:736db4334c89 12
glansberry 0:736db4334c89 13 */
glansberry 0:736db4334c89 14 #include "COBS.h"
glansberry 0:736db4334c89 15 /*
glansberry 0:736db4334c89 16 * StuffData byte stuffs “length” bytes of
glansberry 0:736db4334c89 17 * data at the location pointed to by “ptr”,
glansberry 0:736db4334c89 18 * writing the output to the location pointed
glansberry 0:736db4334c89 19 * to by “dst”.
glansberry 0:736db4334c89 20 */
glansberry 0:736db4334c89 21 #define FinishBlock(X) \
glansberry 0:736db4334c89 22 (*code_ptr = (X), \
glansberry 0:736db4334c89 23 code_ptr = dst++, \
glansberry 0:736db4334c89 24 code = 0x01)
glansberry 0:736db4334c89 25
glansberry 0:736db4334c89 26 /* Stuff the data into an array */
glansberry 0:736db4334c89 27 void COBS::StuffData(unsigned char *ptr, unsigned long length, unsigned char *dst)
glansberry 0:736db4334c89 28 {
glansberry 0:736db4334c89 29 const unsigned char *end = ptr + length;
glansberry 0:736db4334c89 30 unsigned char *code_ptr = dst++;
glansberry 0:736db4334c89 31 unsigned char code = 0x01;
glansberry 0:736db4334c89 32 while (ptr < end)
glansberry 0:736db4334c89 33 {
glansberry 0:736db4334c89 34 if (*ptr == 0) FinishBlock(code);
glansberry 0:736db4334c89 35 else
glansberry 0:736db4334c89 36 {
glansberry 0:736db4334c89 37 *dst++ = *ptr;
glansberry 0:736db4334c89 38 code++;
glansberry 0:736db4334c89 39 if (code == 0xFF) FinishBlock(code);
glansberry 0:736db4334c89 40 }
glansberry 0:736db4334c89 41 ptr++;
glansberry 0:736db4334c89 42 }
glansberry 0:736db4334c89 43
glansberry 0:736db4334c89 44 FinishBlock(code);
glansberry 0:736db4334c89 45 }
glansberry 0:736db4334c89 46
glansberry 0:736db4334c89 47 /*
glansberry 0:736db4334c89 48 * UnStuffData decodes “length” bytes of
glansberry 0:736db4334c89 49 * data at the location pointed to by “ptr”,
glansberry 0:736db4334c89 50 * writing the output to the location pointed
glansberry 0:736db4334c89 51 * to by “dst”.
glansberry 0:736db4334c89 52 */
glansberry 0:736db4334c89 53 void COBS::UnStuffData(unsigned char *ptr, unsigned long length, unsigned char *dst)
glansberry 0:736db4334c89 54 {
glansberry 0:736db4334c89 55 const unsigned char *end = ptr + length;
glansberry 0:736db4334c89 56 while (ptr < end)
glansberry 0:736db4334c89 57 {
glansberry 0:736db4334c89 58 int i, code = *ptr++;
glansberry 0:736db4334c89 59 for (i=1; i<code; i++) *dst++ = *ptr++;
glansberry 0:736db4334c89 60 if (code < 0xFF) *dst++ = 0;
glansberry 0:736db4334c89 61 }
glansberry 0:736db4334c89 62 }