2018/Day19/Day19A.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <inttypes.h>
#include <assert.h>
#include <string.h>

typedef struct {
    uint8_t opcode;
    uint32_t a, b, c;
} Instruction;

Instruction instructions[1024];

enum {
    ADDR, ADDI, MULR, MULI, BANR, BANI, BORR, BORI,
    SETR, SETI, GTIR, GTRI, GTRR, EQIR, EQRI, EQRR,
    IP,
};

const char *names[] = {
    "addr", "addi", "mulr", "muli", "banr", "bani", "borr", "bori",
    "setr", "seti", "gtir", "gtri", "gtrr", "eqir", "eqri", "eqrr",
    "#ip",
};

int instruction_read(Instruction *i, FILE *file) {
    char mnemonic[64] = {0};
    size_t count = fscanf(file, "%s %u %u %u", mnemonic, &i->a, &i->b, &i->c);
    if (count != 4 && count != 2)
        return 0;

    for (int opcode = 0; opcode <= IP; opcode++) {
        if (strcmp(names[opcode], mnemonic) == 0) {
            i->opcode = opcode;
            return 1;
        }
    }
    printf("Unknown mnemonic '%s'\n", mnemonic);
    return 0;
}

void instruction_execute(const Instruction *i, uint32_t *r, uint32_t *ip, uint32_t *ip_r) {
    if (*ip_r != -1)
        r[*ip_r] = *ip;

    switch (i->opcode) {
    // Addition
    case ADDR: r[i->c] = r[i->a] + r[i->b];    break;
    case ADDI: r[i->c] = r[i->a] + i->b;       break;

    // Multiplication
    case MULR: r[i->c] = r[i->a] * r[i->b];    break;
    case MULI: r[i->c] = r[i->a] * i->b;       break;

    // Bitwise AND
    case BANR: r[i->c] = (r[i->a] & r[i->b]);  break;
    case BANI: r[i->c] = (r[i->a] & i->b);     break;

    // Bitwise OR
    case BORR: r[i->c] = (r[i->a] | r[i->b]);  break;
    case BORI: r[i->c] = (r[i->a] | i->b);     break;

    // Assignment
    case SETR: r[i->c] = r[i->a];              break;
    case SETI: r[i->c] = i->a;                 break;

    // Greater-than testing
    case GTIR: r[i->c] = (i->a > r[i->b]);     break;
    case GTRI: r[i->c] = (r[i->a] > i->b);     break;
    case GTRR: r[i->c] = (r[i->a] > r[i->b]);  break;

    // Equality testing
    case EQIR: r[i->c] = (i->a == r[i->b]);    break;
    case EQRI: r[i->c] = (r[i->a] == i->b);    break;
    case EQRR: r[i->c] = (r[i->a] == r[i->b]); break;

    case IP:   *ip_r = i->a; *ip -= 1;         break;

    default: assert(0);
    }

    if (*ip_r != -1)
        *ip = r[*ip_r];

    *ip += 1;
}

int main(int argc, char **argv) {
    if (argc != 2) {
        printf("Usage: %s [input]\n", argv[0]);
        return EXIT_FAILURE;
    }

    FILE *file = fopen(argv[1], "r");

    uint32_t registers[6] = {0};
    uint32_t ip_reg = -1;
    size_t instr_count = 0;
    for (instr_count = 0; instr_count < 1024 && instruction_read(&instructions[instr_count], file); instr_count++) {
#ifdef DEBUG
        printf("opcode: %2d (%s), a: %d, b: %d, c: %d\n", instructions[instr_count].opcode,
               names[instructions[instr_count].opcode], instructions[instr_count].a, instructions[instr_count].b,
               instructions[instr_count].c);
#endif
    }

    for (uint32_t i = 0; i < instr_count;) {
        Instruction instruction = instructions[i];
#ifdef DEBUG
        const char *name = names[instruction.opcode];
        printf("opcode: %2d (%s), a: %d, b: %d, c: %d\n", instruction.opcode,
               name, instruction.a, instruction.b, instruction.c);
#endif

        instruction_execute(&instruction, registers, &i, &ip_reg);

#ifdef DEBUG
        printf("registers: %d %d %d %d %d %d\n", registers[0], registers[1],
               registers[2], registers[3], registers[4], registers[5]);
#endif
    }

    fclose(file);

    printf("%d\n", registers[0]);
    return EXIT_SUCCESS;
}