Just messing around

get_perm_string.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *get_perm_string(unsigned int perm) {
  unsigned int perms_str_size = 17 + 1;
  char *perms = malloc(perms_str_size);
  unsigned int *flags = malloc(sizeof(int) * 6);
  unsigned int shift, offset, i, f, letter, new_size, j;
  char *ret;

  perm &= 07777;

  if ((perm & 0777) == 0777) {
    ret = malloc(5 + 2 + 1);

    sprintf(ret, "u+%s,g+%s,a+%s", "rwx", "rwx", "rwx");

    return ret;
  }

  memset(perms, 0, perms_str_size);

  perms[0] = 'u';
  perms[1] = '+';
  perms[5] = ',';
  perms[6] = 'g';
  perms[7] = '+';
  perms[11] = ',';
  perms[12] = 'o';
  perms[13] = '+';

  for (shift = 00; shift < 011; shift += 03) {
    flags[0] = 0400 >> shift;
    flags[1] = 'r';
    flags[2] = 0200 >> shift;
    flags[3] = 'w';
    flags[4] = 0100 >> shift;
    flags[5] = 'x';

    for (i = 0; i < 6; i += 2) {
      offset = (shift / 3) + (2 + (i/2)) + (5 * (shift / 3));
      f = flags[i];
      letter = flags[i + 1];

      if (perm & f) {
        perms[offset] = letter;
      }
    }
  }

  for (new_size = 0, i = 0; i < perms_str_size; i++) {
    if (perms[i] != 0) {
      new_size++;
    }
  }

  ret = malloc(new_size);
  memset(ret, 0, new_size);

  for (i = 0, j = 0; i < perms_str_size; i++) {
    if (perms[i] != 0) {
      ret[j] = perms[i];
      j++;
    }
  }
  ret[j] = '\0';

  free(perms);
  free(flags);

  return ret;
}

def get_perm_string(perm)
  perm &= 07777

  return ('u+%s,g+%s,r+%s' % ['rwx', 'rwx', 'rwx']) if (perm & 0777) == 0777

  perms = ['u+', 'g+', 'o+']

  [00, 03, 06].collect! do |shift|
    flags = {
      0400 >> shift => 'r',
      0200 >> shift => 'w',
      0100 >> shift => 'x',
    }
    offset = shift / 3

    flags.collect do |f, letter|
      perms[offset] << letter if (perm & f) == f
    end

    perms.delete_at offset if perms[offset].length == 2
  end

  return perms.join(',')
end

puts get_perm_string(010777)
puts get_perm_string(010755)
puts get_perm_string(010644)
puts get_perm_string(010640)