AoC19/d01.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <err.h>
#include <openssl/bn.h>

struct thread_params {
    char *begin;
    char *end;
    BIGNUM *results[2];
};

void *thread(void *arg)
{
    struct thread_params *params = arg;
    char *line = params->begin;
    BIGNUM *cur = NULL;
    while (line && line < params->end && *line) {
        BN_dec2bn(&cur, line);
        BN_div_word(cur, 3);
        BN_sub_word(cur, 2);
        BN_add(params->results[0], params->results[0], cur);
        while (!BN_is_negative(cur) && !BN_is_zero(cur)) {
            BN_add(params->results[1], params->results[1], cur);
            BN_div_word(cur, 3);
            BN_sub_word(cur, 2);
        }
        line = strchr(line, '\n');
        if (line) line++;
    }
    BN_free(cur);
    return NULL;
}

int main(int argc, char *argv[])
{
    long jobs = 8;
    if (argc <= 1) return EXIT_FAILURE;
    if (argc > 2) jobs = strtol(argv[2], NULL, 0);

    FILE *f = fopen(argv[1], "r");
    if (!f) err(EXIT_FAILURE, "fopen");
    fseek(f, 0, SEEK_END);
    long f_len = ftell(f);
    fseek(f, 0, SEEK_SET);
    char *file = malloc(f_len + 1);
    if (!file) err(EXIT_FAILURE, "malloc");
    if (fread(file, f_len, 1, f) != 1) err(EXIT_FAILURE, "fread");
    file[f_len] = '\0';
    fclose(f);

    unsigned lines = 0;
    for (char *c = file; *c; c++) if (*c == '\n') lines++;
    if (file[f_len - 1] != '\n') lines++;

    unsigned lines_per_job = lines / jobs;

    struct thread_params params[jobs];
    pthread_t threads[jobs];
    char *begin = file;
    char *end = begin;
    for (unsigned i = 0; i < jobs; i++) {
        params[i].results[0] = BN_new();
        params[i].results[1] = BN_new();

        if (i == jobs - 1) {
            end = file + strlen(file);
        } else {
            for (unsigned i = 0; i < lines_per_job; i++) {
                end = strchr(end, '\n');
                if (!end) {
                    end = file + strlen(file);
                    break;
                }
                end++;
            }
        }

        params[i].begin = begin;
        params[i].end = end;
        begin = end;

        pthread_create(&threads[i], NULL, thread, &params[i]);
    }

    BIGNUM *result_p1 = BN_new();
    BIGNUM *result_p2 = BN_new();
    for (unsigned i = 0; i < jobs; i++) {
        pthread_join(threads[i], NULL);
        BN_add(result_p1, result_p1, params[i].results[0]);
        BN_add(result_p2, result_p2, params[i].results[1]);
        BN_free(params[i].results[0]);
        BN_free(params[i].results[1]);
    }

    char *result_p1_str = BN_bn2dec(result_p1);
    char *result_p2_str = BN_bn2dec(result_p2);
    BN_free(result_p1);
    BN_free(result_p2);
    printf("Part 1: %s\n", result_p1_str);
    printf("Part 2: %s\n", result_p2_str);
    OPENSSL_free(result_p1_str);
    OPENSSL_free(result_p2_str);
    free(file);
}