SHA512tDigest constructor
      
      SHA512tDigest(
    
    
- int digestSize
Implementation
SHA512tDigest(this.digestSize) {
  if (digestSize >= 64) {
    throw ArgumentError('Digest size cannot be >= 64 bytes (512 bits)');
  }
  if (digestSize == 48) {
    throw ArgumentError(
        'Digest size cannot be 48 bytes (384 bits): use SHA-384 instead');
  }
  _generateIVs(digestSize * 8);
  reset();
}