// data  ---  array of binary data (0s and non-0s)
// Clamp non-zeros to 1
for(int i = 0; i < data_length; ++i)
{
  if(data[i])
  {
    data[i] = 1;
  }
}
// Map 8 elements of 'data' to 1 element of 'compressed'
unsigned char compressed[data_length/8];
for(int i = 0; i < data_length/8; ++i)
{
  compressed[i] = 0x00 | data[i*8];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+1];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+2];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+3];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+4];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+5];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+6];
  compressed[i] = compressed[i]<<1;
  compressed[i] = compressed[i] | data[i*8+7];
}