Add completed PS1

exercises/01/ps1_oyvindps/Makefile

@@ -0,0 +1,4 @@
+CFLAGS+= -g
+scanner: scanner.c
+clean:
+	-rm -f scanner

exercises/01/ps1_oyvindps/scanner.c

@@ -0,0 +1,165 @@
+#define _XOPEN_SOURCE 500
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#define ERROR -1
+#define N_STATES 8
+#define ACCEPT N_STATES
+
+// Buffer for accepted characters, to interpret when in accepting state
+char lexical_buffer[256];
+
+// Program internal state
+int
+    state = 0,                          // Current state in the automaton
+    transition_table[N_STATES][256],    // Table form of the automaton
+    lexical_position = 0,               // Track position in character buffer
+    x = 421, y = 298,                   // Set starting point at page center
+    dx = 0, dy = 0;                     // Horizontal/vertical shift values
+
+
+/*
+ * When a complete command has been scanned, this
+ * function translates it into postscript
+ */
+void interpret_lexical_buffer ( void );
+
+
+/*
+ * Prepare the table form of the automaton
+ */
+void
+initialize_transition_table ( void )
+{
+    memset ( transition_table, 0, N_STATES*256*sizeof(int) );
+    for ( int s=0; s<N_STATES; s++ )
+        for ( int i=0; i<256; i++ )
+            transition_table[s][i] = ERROR;
+
+    // Transition table is based on the following table:
+    // ┌───────┬───┬───┬───┬───┬───┬───────┬───┬───┬────────┐
+    // │ State │ d │ x │ y │ = │ - │ [0-9] │ g │ o │   \n   │
+    // ├───────┼───┼───┼───┼───┼───┼───────┼───┼───┼────────┤
+    // │     0 │ 1 │   │   │   │   │       │ 5 │   │        │
+    // │     1 │   │ 2 │ 2 │   │   │       │   │   │        │
+    // │     2 │   │   │   │ 3 │   │       │   │   │        │
+    // │     3 │   │   │   │   │ 4 │     4 │   │   │        │
+    // │     4 │   │   │   │   │   │     4 │   │   │ ACCEPT │
+    // │     5 │   │   │   │   │   │       │   │ 6 │        │
+    // │     6 │   │   │   │   │   │       │   │   │ ACCEPT │
+    // └───────┴───┴───┴───┴───┴───┴───────┴───┴───┴────────┘
+    // Table is created from regex /(go|d(x|y)=-?[0-9]+)\n/g
+
+    /* STATE 0 */
+    transition_table[0]['d']    = 1;
+    transition_table[0]['g']    = 5;
+
+    /* STATE 1 */
+    transition_table[1]['x']    = 2;
+    transition_table[1]['y']    = 2;
+    
+    /* STATE 2 */
+    transition_table[2]['=']    = 3;
+
+    /* STATE 3 */
+    transition_table[3]['-']    = 4;
+    for (int c = '0'; c <= '9'; c++)
+        transition_table[3][c]    = 4;
+
+    /* STATE 5 */
+    transition_table[4]['\n']   = ACCEPT;
+    for (int c = '0'; c <= '9'; c++)
+        transition_table[4][c]  = 4;
+
+    /* STATE 6 */
+    transition_table[5]['o']    = 6;
+
+    /* STATE 7 */
+    transition_table[6]['\n']   = ACCEPT;
+
+    
+}
+
+
+/* Reset the automaton after completing a command */
+void
+reset ( void )
+{
+    state = 0;
+    lexical_position = 0;
+    memset ( lexical_buffer, 0, 256*sizeof(char) );
+}
+
+
+/*
+ * Main function:
+ *  - Initialize the program to start drawing
+ *  - Scan command
+ *  - Translate accepted command string into postscript
+ *  - Reset automaton
+ *  - Repeat
+ */
+int
+main ()
+{
+    // Prepare the table representation of the automaton
+    initialize_transition_table();
+
+    // Start drawing from the initial coordinates
+    printf ( "<< /PageSize [842 595] >> setpagedevice\n" );
+    printf ( "%d %d moveto\n", x, y );
+
+    // Read characters until end-of-file or failure
+    int read = 0;
+    while ( read != EOF )
+    {
+        // Fetch the next character and store it in the lexical buffer
+        read = getchar();
+        lexical_buffer[lexical_position] = read;
+        lexical_position += 1;
+
+        // Change state according to the table
+        state = transition_table[state][read];
+
+        // Check for error or accepting states:
+        //  * stop the program on error
+        //  * interpret the contents of the lexical buffer when valid
+        switch (state) 
+        {
+            case ERROR:
+                fprintf ( stderr, "Invalid input\n" );
+                exit ( EXIT_FAILURE );
+                break;
+            case ACCEPT:
+                interpret_lexical_buffer();
+                reset();
+                break;
+        }
+    }
+    printf ( "stroke\n" );
+    printf ( "showpage\n" );
+    exit ( EXIT_SUCCESS );
+}
+
+
+/* This function interprets correct statements after they have been accepted */
+void
+interpret_lexical_buffer ( void )
+{
+    if ( lexical_buffer[1] == 'x' )
+        sscanf ( &lexical_buffer[3], "%d", &dx );
+    else if ( lexical_buffer[1] == 'y' )
+        sscanf ( &lexical_buffer[3], "%d", &dy );
+    else if ( strncmp ( lexical_buffer, "go", 2 ) == 0 )
+    {
+        x = x + dx;
+        y = y + dy;
+        printf ( "%d %d lineto\n", x, y );
+        printf ( "%d %d moveto\n", x, y );
+    }
+    else
+        fprintf ( stderr, "Unknown command accepted by the scanner:\n%s\n",
+            lexical_buffer
+        );
+}