start of the array of parameters cons cescparmv0 into cons cescparmp and zeroes

Start of the array of parameters cons cescparmv0 into

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start of the array of parameters, cons->c_esc_parmv[0] into cons->c_esc_parmp, and zeroes into the parameter array itself. Then the first character directly following the ESC is examinedvalid values are either "[" or "M". In the first case the "[" is copied to cons- >c_esc_intro and the state is advanced to 2. In the second case, do_escape is called to carry out the action, and the escape state is reset to zero. If the first character after the ESC is not one of the valid ones, it is ignored and succeeding characters are once again displayed normally. Figure 3-44. Finite state machine for processing escape sequences. [View full size image]
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When an ESC [ sequence has been seen, the next character entered is processed by the escape state 2 code. There are three possibilities at this point. If the character is a numeric character, its value is extracted and added to 10 times the existing value in the position currently pointed to by cons->c_esc_parmp, initially cons->c_esc_parmv[0] (which was initialized to zero). The escape state does not change. This makes it possible to enter a series of decimal digits and accumulate a large numeric parameter, although the maximum value currently recognized by MINIX 3 is 80, used by the sequence that moves the cursor to an arbitrary position (lines 16335 to 16337). If the character is a semicolon there is another parameter, so the pointer to the parameter string is advanced, allowing succeeding numeric values to be accumulated in the second parameter (lines 16339 to 16341). If MAX_ESC_PARMS were to be changed to allocate a larger array for the parameters, this code would not have to be altered to accumulate additional numeric values after entry of additional parameters. Finally, if the character is neither a numeric digit nor a semicolon, do_escape is called. [Page 362] Do_escape (line 16352) is one of the longer functions in the MINIX 3 system source code, even though MINIX 3's complement of recognized escape sequences is relatively modest. For all its length, however, the code should be easy to follow. After an initial call to flush to make sure the video display is fully updated, there is a simple if choice, depending upon whether the character immediately following the ESC character was a special control sequence introducer or not. If not, there is only one valid action, moving the cursor up one line if the sequence was ESC M. Note that the test for the "M" is done within a switch with a default action, as a validity check and in anticipation of addition of other sequences that do not use the ESC [ format. The action is typical of many escape sequences: the cons->c_row variable is inspected to determine if scrolling is required. If the cursor is already on row 0, a SCROLL_DOWN call is made to scroll_screen; otherwise the cursor is moved up one line. The latter is accomplished just by decrementing cons->c_row and then calling flush. If a control sequence introducer is found, the code following the else on line 16377 is taken. A test is made for "[", the only control sequence introducer currently recognized by MINIX 3. If the sequence is valid,
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