Morse code decoder automaton

morsecode.c

/* Morse code decoder automaton
 * This is free and unencumbered software released into the public domain.
 */

/* Advance to the next state for an input, '.', '-'. or 0 (terminal).
 * The initial state is zero. Returns the next state, or the result:
 *   < 0 when more input is needed (i.e. next state)
 *   = 0 for invalid input
 *   > 0 the ASCII result
 */
int
morse_decode(int state, int c)
{
    static const unsigned char t[] = {
        0x03, 0x3f, 0x7b, 0x4f, 0x2f, 0x63, 0x5f, 0x77, 0x7f, 0x72,
        0x87, 0x3b, 0x57, 0x47, 0x67, 0x4b, 0x81, 0x40, 0x01, 0x58,
        0x00, 0x68, 0x51, 0x32, 0x88, 0x34, 0x8c, 0x92, 0x6c, 0x02,
        0x03, 0x18, 0x14, 0x00, 0x10, 0x00, 0x00, 0x00, 0x0c, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x08, 0x1c, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x00, 0x00, 0x00, 0x24,
        0x00, 0x28, 0x04, 0x00, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35,
        0x36, 0x37, 0x38, 0x39, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46,
        0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
        0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a
    };
    int v = t[-state];
    switch (c) {
    case 0x00: return v >> 2 ? t[(v >> 2) + 63] : 0;
    case 0x2e: return v &  2 ? state*2 - 1 : 0;
    case 0x2d: return v &  1 ? state*2 - 2 : 0;
    default:   return 0;
    }
}


#ifdef TEST
#include <stdio.h>
#include <string.h>

#define CR(s) "\x1b[91;1m" s "\x1b[0m"
#define CG(s) "\x1b[92;1m" s "\x1b[0m"

int
main(void)
{
#ifdef _WIN32
    /* Best effort enable ANSI escape processing. */
    void *GetStdHandle(unsigned);
    int GetConsoleMode(void *, unsigned *);
    int SetConsoleMode(void *, unsigned);
    void *handle;
    unsigned mode;
    handle = GetStdHandle(-11); /* STD_OUTPUT_HANDLE */
    if (GetConsoleMode(handle, &mode)) {
        mode |= 0x0004; /* ENABLE_VIRTUAL_TERMINAL_PROCESSING */
        SetConsoleMode(handle, mode); /* ignore errors */
    }
#endif

    static const struct {
        char input[6];
        char expect;
    } tests[] = {
        {"",       0 }, {".",     'E'}, {"-",     'T'}, {"..",    'I'},
        {".-",    'A'}, {"-.",    'N'}, {"--",    'M'}, {"...",   'S'},
        {"..-",   'U'}, {".-.",   'R'}, {".--",   'W'}, {"-..",   'D'},
        {"-.-",   'K'}, {"--.",   'G'}, {"---",   'O'}, {"....",  'H'},
        {"...-",  'V'}, {"..-.",  'F'}, {"..--",   0 }, {".-..",  'L'},
        {".-.-",   0 }, {".--.",  'P'}, {".---",  'J'}, {"-...",  'B'},
        {"-..-",  'X'}, {"-.-.",  'C'}, {"-.--",  'Y'}, {"--..",  'Z'},
        {"--.-",  'Q'}, {"---.",   0 }, {"----",   0 }, {".....", '5'},
        {"....-", '4'}, {"...-.",  0 }, {"...--", '3'}, {"..-..",  0 },
        {"..-.-",  0 }, {"..--.",  0 }, {"..---", '2'}, {".-...",  0 },
        {".-..-",  0 }, {".-.-.",  0 }, {".-.--",  0 }, {".--..",  0 },
        {".--.-",  0 }, {".---.",  0 }, {".----", '1'}, {"-....", '6'},
        {"-...-",  0 }, {"-..-.",  0 }, {"-..--",  0 }, {"-.-..",  0 },
        {"-.-.-",  0 }, {"-.--.",  0 }, {"-.---",  0 }, {"--...", '7'},
        {"--..-",  0 }, {"--.-.",  0 }, {"--.--",  0 }, {"---..", '8'},
        {"---.-",  0 }, {"----.", '9'}, {"-----", '0'},
    };

    int fails = 0;
    int n, ntests = sizeof(tests) / sizeof(*tests);

    for (n = 0; n < ntests; n++) {
        const char *s = tests[n].input;
        int expect = tests[n].expect;
        int pass = 1;
        int state = 0;

        while (*s) {
            state = morse_decode(state, *s++);

            if (!state) {
                if (expect) {
                    printf(CR("FAIL") ": %s, want %c, got early error\n",
                           tests[n].input, expect);
                    pass = 0;
                }
                break;
            }

            if (state > 0) {
                printf(CR("FAIL") ": %s, want %c, got early 0x%02x\n",
                        tests[n].input, expect, state);
                pass = 0;
                break;
            }
        }

        if (state < 0) {
            state = morse_decode(state, 0);

            if (!state) {
                if (expect) {
                    printf(CR("FAIL") ": %s, want %c, got error\n",
                            tests[n].input, expect);
                    pass = 0;
                }
            } else if (state < 0) {
                printf(CR("FAIL") ": %s, want %c, got continuation\n",
                        tests[n].input, expect);
                pass = 0;
            } else if (state != expect) {
                if (expect) {
                    printf(CR("FAIL") ": %s, want %c, got 0x%02x\n",
                            tests[n].input, expect, state);
                } else {
                    printf(CR("FAIL") ": %s, want error, got 0x%02x (%c)\n",
                            tests[n].input, state, state);
                }
                pass = 0;
            }
        }

        if (pass) {
            if (expect) {
                printf(CG("PASS") ": %c %s\n", expect, tests[n].input);
            } else {
                printf(CG("PASS") ": ? %s\n", tests[n].input);
            }
        }

        fails += !pass;
    }

    if (!fails) {
        printf("All %d tests pass\n", ntests);
    }

    return !!fails;
}
#endif