base: Use a simple tricky to remove a temporary variable in MD5DigestToBase16.

base: Use a simple tricky to remove a temporary variable in MD5DigestToBase16.

With this tricky we don't need this strange 'j' variable laying around
outside the loop, even better, since that variable is not even used
outside of the for loop.

The iteration using this tricky goes like the following:

The old tricky using just 'i':
For i = 0:
    0 * 2     = 0
    0 * 2 + 1 = 1

For i = 1:
    1 * 2     = 2
    1 * 2 + 1 = 3

For i = 2:
    2 * 2     = 4
    2 * 2 + 1 = 5

The new tricky using 'j':
For i = 0:
    j = 0
    0     = 0
    0 + 1 = 1

For i = 1:
    j = 2
    2     = 2
    2 + 1 = 3

For i = 2:
    j = 4
    4     = 4
    4 + 1 = 5

So the new code does the same thing as the old but with the advantage of
not having to use a temporary variable outside the loop.

And the tricky with 'j' has also the benefit of avoid a multiplication and the rules of operator precedence.

BUG=None
TEST=base_unittests --gtest_filter=MD5*
R=thestig@chromium.org

Committed: https://crrev.com/fb9d8f3c20dc9d3024355ee989c72c4c4bf8d835
Cr-Commit-Position: refs/heads/master@{#324171}

[Lei Zhang, 2015-04-07 21:44:05]

If you just want to move j into the loop, you can do:

for (int i = 0, j = 0; i < 16; i++, j+=2) {
  func(j);
  func(j + 1);
}

[tfarina, 2015-04-07 23:25:30]

Cool. It avoids a multiplication and operator precedence rules.

Done. ptal

[Lei Zhang, 2015-04-07 23:28:29]

lgtm

This only works when i and j are of the same type.

[tfarina, 2015-04-07 23:55:01]

The CQ bit was checked by tfarina@chromium.org

[commit-bot: I haz the power, 2015-04-07 23:55:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1065733005/20001

[commit-bot: I haz the power, 2015-04-08 01:40:30]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-08 01:41:16]

Patchset 2 (id:??) landed as
https://crrev.com/fb9d8f3c20dc9d3024355ee989c72c4c4bf8d835
Cr-Commit-Position: refs/heads/master@{#324171}