waiwai

day18.c

int table[255] = {0};
int mark = 0xdeadbeef;
int index = 0;

void generate_table()
{
    for(index; index < 0xff; index++) {
        if(table[index] == 0) {
            table[index] = mark;
        } else if((index+1)&2) {
            table[index] += table[index-2];
        }
        table[index+1] = table[index]/(index+1)+2*index*table[index];
    }
}

int get_from_table()
{
    tmp = table[index++];
    return tmp;
}

bool len_check(double pos)
{
    const double fx = 65536.0;
    const double fy = 0.00018310546875;

    pos = fx / pos;
    return (not_parity(pos, fy) || pos != fy)? true : false;
}

int main(void)
{
    char ch, *end;
    int i, j, nullpos = -1, val = 0;

    if(argc != 2) {
        return 1;
    }

    for(i = 0; nullpos--, (argv[1])[i] != '\0'; i++); 
    end = &buf[i];
    nullpos = -2 - (nullpos);

    if(len_check((double)nullpos)) {
        return 1;
    }

    generate_table();

    for(i = 0; i < nullpos; i++) {
        ch = (argv[1])[i];
        index = (int)ch+i;
        if(('0' <= ch && ch <= '9') ||
           ('A' <= ch && ch <= 'Z') ||
           ('a' <= ch && ch <= 'z')) {
            for(j = 0; j < nullpos; j++) {
                val += get_from_table();
            }
            if(check_table[i] != val) {
                return 1;
            }
        } else {
            return 1;
        }
    }
    printf("you got flag: ADCTF_%s\n", argv[1]);

    return 0;
}