#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <math.h>

struct packet_s {
    char range;
    char digits[5];
    char function;
    char status;
    char options[4];
    char eol[2];
};

enum unit_e {
    U_UNKNOWN = 0,
    U_VOLTAGE,
    U_CURRENT,
    U_RESISTANCE,
    U_FREQUENCY,
    U_CAPACITANCE,
    U_ADP // ???
};

struct range_entry_s {
    uint8_t divider;    // Where to place the decimal point
    int8_t exponent;   // 0->Unit 3->KUnit 6->MUnit -3->mUnit -6->uUnit ...
};

char *units[] = { "?", "V", "A", "Ohm", "Hz", "F", "?" };

enum unit_e function_unit[] = {
    U_CURRENT,      // 22A
    U_VOLTAGE,      // Diode
    U_FREQUENCY,
    U_RESISTANCE,
    U_UNKNOWN,      // Temperature
    U_RESISTANCE,   // Continuity
    U_CAPACITANCE,
    U_UNKNOWN,
    U_UNKNOWN,
    U_CURRENT,      // Manual current
    U_UNKNOWN,
    U_VOLTAGE,
    U_UNKNOWN,
    U_CURRENT,      // Auto uA
    U_UNKNOWN,      // ADP
    U_CURRENT       // Auto mA
};

struct range_entry_s ranges[8][16] = {
    // 22A       Diode     Freq      Resist    Temp      Cont      Capac     ?         ?         Man A     ?         V         ?         Auto uA   ADP       Auto mA       
    { { 3, 0 }, { 4, 0 }, { 2, 0 }, { 2, 0 }, { 0, 0 }, { 2, 0 }, { 3, -9}, { 0, 0 }, { 0, 0 }, { 4, 0 }, { 0, 0 }, { 4, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 1, 0 }, { 4, 3 }, { 0, 0 }, { 0, 0 }, { 2, -9}, { 0, 0 }, { 0, 0 }, { 3, 0 }, { 0, 0 }, { 3, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 0, 0 }, { 3, 3 }, { 0, 0 }, { 0, 0 }, { 4, -6}, { 0, 0 }, { 0, 0 }, { 2, 0 }, { 0, 0 }, { 2, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 3, 3 }, { 2, 3 }, { 0, 0 }, { 0, 0 }, { 3, -6}, { 0, 0 }, { 0, 0 }, { 1, 0 }, { 0, 0 }, { 1, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 2, 3 }, { 4, 6 }, { 0, 0 }, { 0, 0 }, { 2, -6}, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 2, -3}, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 4, 6 }, { 3, 6 }, { 0, 0 }, { 0, 0 }, { 4, -3}, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 3, 6 }, { 2, 6 }, { 0, 0 }, { 0, 0 }, { 3, -3}, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } },
    { { 0, 0 }, { 0, 0 }, { 2, 6 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 2, -3}, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 }, { 0, 0 } }
};

int parse_packet(struct packet_s *packet) {
    int32_t number;
    double reading;
    int i;
    int range, function;
    struct range_entry_s re;

    for (number = 0, i = 0; i < sizeof(packet->digits); i++) {
        number *= 10;
        number += packet->digits[i] & 0x0f;
    }

    printf("%6d <- %s", number, (char *)packet);
    
    range = packet->range & 0x07;
    function = packet->function & 0x0f;

    re = ranges[range][function];

    if ((re.divider == 0) && (re.exponent == 0)) {
        printf("Invalid function/range combo: f=%x r=%x\n", function, range);
    }

    reading = number * pow(10.0, re.exponent - re.divider);

    printf("Reading = %lf %s\n", reading, units[function_unit[function]]);

    return 0;
}

void log_packet(struct packet_s *packet) {
    int i;
    char *c = (char *)packet;

    for (i=0; i<sizeof(*packet); i++)
        putc(c[i], stderr);
}

int read_packet(struct packet_s *packet) {
    char ring[sizeof(*packet)];
    char *p;
    int ring_pos;
    char c;
    int ch;
    int shift;

    p = (char *)packet;
    ring_pos = 0;
    shift = sizeof(*packet);
    for (;;) {
        ch = getc(stdin);
        if (ch == EOF)
            return 0;
        c = (char) ch;
        ring[ring_pos] = c;
        ring_pos = (ring_pos + 1) % sizeof(*packet);
        if (((c & 0xf0) != 0x30) && (c != '\r') && (c != '\n')) {
            shift = sizeof(*packet);
        } else {
            if ((c == '\r') && (shift != 2)) {
                shift = sizeof(*packet);
                continue;
            }
            if (c == '\n') {
                if (shift == 1) {
                    for (int i=0; i<sizeof(ring); i++)
                        p[i] = ring[(ring_pos + i) % sizeof(*packet)];
                    log_packet(packet);
                    return 1;
                }
                shift = sizeof(*packet);
                continue;
            }
            shift = (shift > 0) ? shift - 1 : 0;
        }
    }
}

int main() {
    struct packet_s packet;

    while (read_packet(&packet)) {
        parse_packet(&packet);
    }

    return EXIT_SUCCESS;
}