From 5373fbcd1140a9fb4b2e259c04cdd79d4b80bc3b Mon Sep 17 00:00:00 2001 From: Denis Vlasenko Date: Tue, 14 Oct 2008 10:09:56 +0000 Subject: [PATCH] vi: add comments to Rob's algorithm of reading and matching ESC sequences (nice work btw!) --- editors/vi.c | 56 +++++++++++++++++++++++++++++++--------------------- 1 file changed, 33 insertions(+), 23 deletions(-) diff --git a/editors/vi.c b/editors/vi.c index 3c3d759e5..e1cd7a482 100644 --- a/editors/vi.c +++ b/editors/vi.c @@ -2243,60 +2243,70 @@ static char readit(void) // read (maybe cursor) key from stdin fflush(stdout); - // If no data, block waiting for input. n = chars_to_parse; - while (!n) { + if (n == 0) { + // If no data, block waiting for input. n = safe_read(0, readbuffer, 1); if (n <= 0) { + error: place_cursor(rows - 1, 0, FALSE); // go to bottom of screen clear_to_eol(); // erase to end of line cookmode(); // terminal to "cooked" bb_error_msg_and_die("can't read user input"); } - // Returning NUL from this routine would be bad. - if (*readbuffer) break; } // Grab character to return from buffer - c = *readbuffer; + c = readbuffer[0]; + // Returning NUL from this routine would be bad. + if (c == '\0') + c = ' '; n--; - if (n) memmove(readbuffer, readbuffer+1, n); + if (n) memmove(readbuffer, readbuffer + 1, n); // If it's an escape sequence, loop through known matches. if (c == 27) { const struct esc_cmds *eindex; - for (eindex = esccmds; eindex < esccmds+ARRAY_SIZE(esccmds); eindex++) { - int i=0, cnt = strnlen(eindex->seq, 4); + for (eindex = esccmds; eindex < esccmds + ARRAY_SIZE(esccmds); eindex++) { + // n - position in seq to read + int i = 0; // position in seq to compare + int cnt = strnlen(eindex->seq, 4); // Loop through chars in this sequence. for (;;) { - - // If we've matched this escape sequence so far but need more - // chars, read another as long as it wouldn't block. (Note that - // escape sequences come in as a unit, so if we would block - // it's not really an escape sequence.) + // We've matched this escape sequence up to [i-1] if (n <= i) { + // Need more chars, read another one if it wouldn't block. + // (Note that escape sequences come in as a unit, + // so if we would block it's not really an escape sequence.) struct pollfd pfd; pfd.fd = 0; pfd.events = POLLIN; - if (0 < safe_poll(&pfd, 1, 300) - && 0 < safe_read(0, readbuffer + n, 1)) - n++; - - // Since the array is sorted from shortest to longest, if - // we needed more data we can't match anything later, so - // break out of both loops. - else goto loop_out; + // TODO: what is a good timeout here? why? + if (safe_poll(&pfd, 1, /*timeout:*/ 0)) { + if (safe_read(0, readbuffer + n, 1) <= 0) + goto error; + n++; + } else { + // No more data! + // Array is sorted from shortest to longest, + // we can't match anything later in array, + // break out of both loops. + goto loop_out; + } } - if (readbuffer[i] != eindex->seq[i]) break; - if (++i == cnt) { + if (readbuffer[i] != eindex->seq[i]) + break; // try next seq + if (++i == cnt) { // entire seq matched c = eindex->val; n = 0; goto loop_out; } } } + // We did not find matching sequence, it was a bare ESC. + // We possibly read and stored more input in readbuffer by now. } loop_out: -- 2.25.1