Adds a base32 component.

components/base32/base32.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/base32/base32.h"
+
+#include <stddef.h>
+#include <algorithm>
+
+namespace base32 {
+
+namespace {
+const char kEncoding[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";
+}  // namespace
+
+void Base32Encode(base::StringPiece input,
+                  Base32EncodePolicy policy,
+                  std::string* output) {
+  output->clear();
+
+  // Transform 5 input bytes into 8 output bytes at a time.
+  // Based on the encoding process described in RFC4648, section 6.
+  for (size_t input_offset = 0; input_offset < input.size();
+       input_offset += 5) {
+    // Bits of input left to encode.
+    size_t bits_remaining =
+        std::min(size_t(5), input.size() - input_offset) * 8;
+    // A buffer for up to 40 bits of input that is consumed 5 bits at a time.
+    // 40 bits is used because it is the lowest common multiple of 5 and 8.
+    uint64_t input_group = 0;
+
+    // Load 8 bits at a time into the buffer.
+    // Can't simply memcpy because of endianness.
+    for (size_t i = 0; i < bits_remaining / 8; ++i) {
+      input_group <<= 8;
+      input_group |= static_cast<uint8_t>(input[input_offset + i]);
+    }
+    // Shift the bits we've set to start at the MSB, for ease of access.
+    input_group <<= (64 - bits_remaining);
+
+    // Output the |input_group| as up to 8 bytes in base32.
+    // If we run out of bits, padding will make up the remaining bytes
+    // (unless |policy| dictates otherwise).
+    for (size_t output_count = 0; output_count < 8; ++output_count) {
+      if (bits_remaining == 0) {
+        if (policy == Base32EncodePolicy::INCLUDE_PADDING)
+          output->append(8 - output_count, '=');
+        break;
+      }
+      // Encode the first 5 bits, then shift them out of the buffer.
+      output->push_back(kEncoding[input_group >> 59]);
+      input_group <<= 5;
+      // Subtract 5 bits, or however many are left, whichever is smaller.
+      bits_remaining -= (bits_remaining >= 5) ? 5 : bits_remaining;
+    }
+  }
+}
+
+}  // namespace base32