166 lines
5.0 KiB
C
166 lines
5.0 KiB
C
#define _XOPEN_SOURCE 500
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#define ERROR -1
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#define N_STATES 8
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#define ACCEPT N_STATES
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// Buffer for accepted characters, to interpret when in accepting state
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char lexical_buffer[256];
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// Program internal state
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int
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state = 0, // Current state in the automaton
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transition_table[N_STATES][256], // Table form of the automaton
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lexical_position = 0, // Track position in character buffer
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x = 421, y = 298, // Set starting point at page center
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dx = 0, dy = 0; // Horizontal/vertical shift values
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/*
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* When a complete command has been scanned, this
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* function translates it into postscript
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*/
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void interpret_lexical_buffer ( void );
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/*
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* Prepare the table form of the automaton
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*/
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void
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initialize_transition_table ( void )
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{
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memset ( transition_table, 0, N_STATES*256*sizeof(int) );
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for ( int s=0; s<N_STATES; s++ )
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for ( int i=0; i<256; i++ )
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transition_table[s][i] = ERROR;
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// Transition table is based on the following table:
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// ┌───────┬───┬───┬───┬───┬───┬───────┬───┬───┬────────┐
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// │ State │ d │ x │ y │ = │ - │ [0-9] │ g │ o │ \n │
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// ├───────┼───┼───┼───┼───┼───┼───────┼───┼───┼────────┤
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// │ 0 │ 1 │ │ │ │ │ │ 5 │ │ │
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// │ 1 │ │ 2 │ 2 │ │ │ │ │ │ │
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// │ 2 │ │ │ │ 3 │ │ │ │ │ │
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// │ 3 │ │ │ │ │ 4 │ 4 │ │ │ │
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// │ 4 │ │ │ │ │ │ 4 │ │ │ ACCEPT │
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// │ 5 │ │ │ │ │ │ │ │ 6 │ │
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// │ 6 │ │ │ │ │ │ │ │ │ ACCEPT │
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// └───────┴───┴───┴───┴───┴───┴───────┴───┴───┴────────┘
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// Table is created from regex /(go|d(x|y)=-?[0-9]+)\n/g
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/* STATE 0 */
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transition_table[0]['d'] = 1;
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transition_table[0]['g'] = 5;
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/* STATE 1 */
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transition_table[1]['x'] = 2;
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transition_table[1]['y'] = 2;
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/* STATE 2 */
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transition_table[2]['='] = 3;
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/* STATE 3 */
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transition_table[3]['-'] = 4;
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for (int c = '0'; c <= '9'; c++)
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transition_table[3][c] = 4;
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/* STATE 5 */
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transition_table[4]['\n'] = ACCEPT;
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for (int c = '0'; c <= '9'; c++)
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transition_table[4][c] = 4;
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/* STATE 6 */
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transition_table[5]['o'] = 6;
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/* STATE 7 */
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transition_table[6]['\n'] = ACCEPT;
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}
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/* Reset the automaton after completing a command */
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void
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reset ( void )
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{
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state = 0;
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lexical_position = 0;
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memset ( lexical_buffer, 0, 256*sizeof(char) );
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}
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/*
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* Main function:
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* - Initialize the program to start drawing
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* - Scan command
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* - Translate accepted command string into postscript
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* - Reset automaton
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* - Repeat
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*/
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int
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main ()
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{
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// Prepare the table representation of the automaton
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initialize_transition_table();
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// Start drawing from the initial coordinates
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printf ( "<< /PageSize [842 595] >> setpagedevice\n" );
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printf ( "%d %d moveto\n", x, y );
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// Read characters until end-of-file or failure
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int read = 0;
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while ( read != EOF )
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{
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// Fetch the next character and store it in the lexical buffer
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read = getchar();
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lexical_buffer[lexical_position] = read;
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lexical_position += 1;
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// Change state according to the table
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state = transition_table[state][read];
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// Check for error or accepting states:
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// * stop the program on error
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// * interpret the contents of the lexical buffer when valid
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switch (state)
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{
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case ERROR:
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fprintf ( stderr, "Invalid input\n" );
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exit ( EXIT_FAILURE );
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break;
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case ACCEPT:
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interpret_lexical_buffer();
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reset();
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break;
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}
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}
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printf ( "stroke\n" );
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printf ( "showpage\n" );
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exit ( EXIT_SUCCESS );
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}
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/* This function interprets correct statements after they have been accepted */
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void
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interpret_lexical_buffer ( void )
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{
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if ( lexical_buffer[1] == 'x' )
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sscanf ( &lexical_buffer[3], "%d", &dx );
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else if ( lexical_buffer[1] == 'y' )
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sscanf ( &lexical_buffer[3], "%d", &dy );
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else if ( strncmp ( lexical_buffer, "go", 2 ) == 0 )
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{
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x = x + dx;
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y = y + dy;
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printf ( "%d %d lineto\n", x, y );
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printf ( "%d %d moveto\n", x, y );
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}
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else
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fprintf ( stderr, "Unknown command accepted by the scanner:\n%s\n",
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lexical_buffer
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);
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}
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