Design and Implementation of a Documentation Tool for ... - MADOC

A.4 Magic Number
Since a forscript file has to start with a file version chunk followed by a begin
of session chunk, there is a distinctive eight-byte signature at the beginning of
each file:
0x0e 0x0e 0x01 0x?? 0x0f 0x0e 0x0e 0x02
The first two bytes start a metadata chunk, the third one identifies it as a file
version chunk. The fourth byte contains the version number, which is currently
0x01 but may change in the future. Byte 5 closes the version chunk, 5 to 8 start
a begin of session chunk.
A.5 Writing Metadata Chunks to Disk
The function chunkwd() takes a pointer and a byte count as arguments and
writes chunk data to the transcript file, applying required escapes on the fly. To
improve performance, it does not write byte-by-byte, but instead scans the input
data until it finds a special character. When it does, it writes everything up to,
but not including, the special character to the file and then adds a DLE character.
The search then goes on. If another special character is found, everything
from the last special character (inclusive) to the current one (exclusive) plus a
DLE is written. Eventually the whole input data will have been scanned and
the function terminates after writing everything from the last special character
(inclusive) or the beginning of the data (if there were no special characters) to
the end of the input data. This is the code:
21 〈chunkw 21〉≡ (15c)
int chunkwd(unsigned char *data, int count) {
int escaped = 0;
int pos = 0;
int start = 0;
while (pos < count) {
if (data[pos] = ESCMIN) {
if (pos > start) {
if (!swrite(&data[start], sizeof(char),
pos - start, OUTF))
return -1;
}
if (!swrite(&DLE, sizeof(DLE), 1, OUTF))
return -2;
start = pos;
escaped++;
}
pos++;
}
if (!swrite(&data[start], sizeof(char),
pos - start, OUTF))
return -3;
return escaped;
21