Repack cossacks resources.gsc (all.gsc) from Russian to English version.

main.c

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

#define INPUT_KEY 0x4EBA // Input key (Russian)
#define OUTPUT_KEY 0x78CD // Output key (English)

#define CHUNK_SIZE 1024 * 1024 // 1MB

int main(int argc, char *argv[]) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <INPUT_FILE> <OUTPUT_FILE>\n", argv[0]);
        return -1;
    }

    char *input_file = argv[1];
    char *output_file = argv[2];

    FILE *inf = fopen(input_file, "rb");
    if (inf == NULL) {
        fprintf(stderr, "Failed to open input file.\n");
        return -1;
    }

    FILE *outf = fopen(output_file, "wb");
    if (outf == NULL) {
        fprintf(stderr, "Failed to open output file.\n");
        fclose(inf);
        return -1;
    }

    uint64_t in_key = ~(INPUT_KEY >> 8);
    uint64_t out_key = ~(OUTPUT_KEY >> 8);

    for (int i = 1; i < 8; ++i) {
        in_key = in_key | ((in_key & 0xFF) << i);
        out_key = out_key | ((out_key & 0xFF) << i);
    }

    fseek(inf, 0, SEEK_END);
    size_t file_size = ftell(inf);
    fseek(inf, 0, SEEK_SET);

    int chunk_counter = 0;
    int chunk_count = (int) ceil(((double) file_size) / ((double) CHUNK_SIZE));

    uint8_t *chunk = (uint8_t *) malloc(CHUNK_SIZE);
    size_t count;

    printf("File size: %d\n", file_size);
    printf("Chunk count: %d\n", chunk_count);

    while ((count = fread(chunk, 1, CHUNK_SIZE, inf)) > 0) {
        size_t i = 0;
        for (; i < (count / 8) * 8; i += 8) {
            uint64_t value = *((uint64_t *) (chunk + i));

            value = ~value;
            value = value ^ in_key;

            value = value ^ out_key;
            value = ~value;

            *((uint64_t *) (chunk + i)) = value;
        }

        for (; i < count; ++i) {
            uint8_t value = chunk[i];

            value = ~value;
            value = value ^ (in_key & 0xFF);

            value = value ^ (out_key & 0xFF);
            value = ~value;

            chunk[i] = value;
        }

        ++chunk_counter;
        printf("Progress %d/%d chunks\n", chunk_counter, chunk_count);

        fwrite(chunk, 1, count, outf);
    }

    free(chunk);
    fclose(inf);
    fclose(outf);

    return 0;
}