Update documentation comments.

lib/src/sha256.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library crypto.sha256;
 
 import 'dart:typed_data';
 
 import 'hash.dart';
 import 'hash_base.dart';
 import 'utils.dart';
 
-/**
- * SHA256 hash function implementation.
- */
+/// An implementation of the [SHA-256][rfc] hash function.
+///
+/// [rfc]: http://tools.ietf.org/html/rfc6234
 abstract class SHA256 implements Hash {
   factory SHA256() = _SHA256;
 
   SHA256 newInstance();
 }
 
+/// The concrete implementation of [SHA256].
+///
+/// This is separate so that it can extend [HashBase] without leaking additional
+/// public memebers.
 class _SHA256 extends HashBase implements SHA256 {
+  /// The sixteen words from the original chunk, extended to 64 words.
+  ///
+  /// This is an instance variable to avoid re-allocating, but its data isn't
+  /// used across invocations of [updateHash].
   final Uint32List _w;
 
-  // Construct a SHA256 hasher object.
   _SHA256()
       : _w = new Uint32List(64),
         super(16, 8, true) {
     // Initial value of the hash parts. First 32 bits of the fractional parts
     // of the square roots of the first 8 prime numbers.
     h[0] = 0x6a09e667;
     h[1] = 0xbb67ae85;
     h[2] = 0x3c6ef372;
     h[3] = 0xa54ff53a;
     h[4] = 0x510e527f;
     h[5] = 0x9b05688c;
     h[6] = 0x1f83d9ab;
     h[7] = 0x5be0cd19;
   }
 
-  // Returns a new instance of this Hash.
   SHA256 newInstance() {
     return new _SHA256();
   }
 
-  // Table of round constants. First 32 bits of the fractional
-  // parts of the cube roots of the first 64 prime numbers.
+  /// Data from a non-linear function that functions as reproducible noise.
   static const List<int> _K = const [
     0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b,
     0x59f111f1, 0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01,
     0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7,
     0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
     0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152,
     0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
     0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc,
     0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
     0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819,
     0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116, 0x1e376c08,
     0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f,
     0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
     0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
   ];
 
-  // Helper functions as defined in http://tools.ietf.org/html/rfc6234
+  // The following helper functions are taken directly from
+  // http://tools.ietf.org/html/rfc6234.
+
   _rotr32(n, x) => (x >> n) | ((x << (32 - n)) & MASK_32);
   _ch(x, y, z) => (x & y) ^ ((~x & MASK_32) & z);
   _maj(x, y, z) => (x & y) ^ (x & z) ^ (y & z);
   _bsig0(x) => _rotr32(2, x) ^ _rotr32(13, x) ^ _rotr32(22, x);
   _bsig1(x) => _rotr32(6, x) ^ _rotr32(11, x) ^ _rotr32(25, x);
   _ssig0(x) => _rotr32(7, x) ^ _rotr32(18, x) ^ (x >> 3);
   _ssig1(x) => _rotr32(17, x) ^ _rotr32(19, x) ^ (x >> 10);
 
-  // Compute one iteration of the SHA256 algorithm with a chunk of
-  // 16 32-bit pieces.
   void updateHash(Uint32List M) {
     assert(M.length == 16);
 
     // Prepare message schedule.
     var i = 0;
     for (; i < 16; i++) {
       _w[i] = M[i];
     }
     for (; i < 64; i++) {
       _w[i] = add32(add32(_ssig1(_w[i - 2]), _w[i - 7]),
@@ skipping 28 matching lines @@
     h[0] = add32(a, h[0]);
     h[1] = add32(b, h[1]);
     h[2] = add32(c, h[2]);
     h[3] = add32(d, h[3]);
     h[4] = add32(e, h[4]);
     h[5] = add32(f, h[5]);
     h[6] = add32(g, h[6]);
     h[7] = add32(j, h[7]);
   }
 }