Small function to compute the sha1 sum of data in c++

Sha1Sum.cc

#include <boost/uuid/sha1.hpp>
#include <sstream>
#include <cstddef>
#include <string>

std::string Sha1sum(void *data, std::size_t count) {
  boost::uuids::detail::sha1 hasher;
  char hash[20];
  hasher.process_bytes(data, count);
  unsigned int digest[5];
  hasher.get_digest(digest);
  for(int i = 0; i < 5; ++i) {
    const char *tmp = reinterpret_cast<char *>(digest);
    hash[i * 4] = tmp[i * 4 + 3];
    hash[i * 4 + 1] = tmp[i * 4 + 2];
    hash[i * 4 + 2] = tmp[i * 4 + 1];
    hash[i * 4 + 3] = tmp[i * 4];
  }
  std::stringstream res;
  res << std::hex;
  for(int i = 0; i < 20; ++i) {
      res << ((hash[i] & 0x000000F0) >> 4)
         <<  (hash[i] & 0x0000000F);
  }
  return res.str();
}