nix-base32.cpp

#include <iostream>
#include <string>

using namespace std;

unsigned int hashLength32(string hash) {
  return (hash.length() * 8 - 1) / 5 + 1;
}

// omitted: E O U T
const string base32Chars = "0123456789abcdfghijklmnpqrsvwxyz";

string printHash32(string hash) {
  unsigned int len = hashLength32(hash);

  string s;
  s.reserve(len);

  for (int n = len - 1; n >= 0; n--) {
    unsigned int b = n * 5;
    unsigned int i = b / 8;
    unsigned int j = b % 8;
    unsigned char c =
      (hash[i] >> j)
      | (i >= hash.length() - 1 ? 0 : hash[i + 1] << (8 - j));
    s.push_back(base32Chars[c & 0x1f]);
  }

  return s;
}

int main() {
  for (string line; std::getline(cin, line);) {
    cout << printHash32(line) << endl;
  }  
}