ssh/terminal: Use move-N sequences for >1 cursor moves

Before, we emitted N single-move sequences on a cursor move. For
example, "move 4 left" would emit "^[[D^[[D^[[D^[[D". With this change,
it would emit "^[[4D".

Using variable move sequences when possible reduces the amount of
rendering output that the terminal implementation produces. This can
have some low-level performance benefits, but also helps consumers
reason through the produced output.

Includes a test with a couple of cases.

Note: The old implementation used ^[[D instead of ^[D which is also
valid. This is true in several unrelated places, so this implementation
continues to use ^[[D for consistency.

Change-Id: If38eaaed8fb4075499fdda54c06681dc34c3ad70
GitHub-Last-Rev: 92ef2538d33a9493f3df09984c277dfd8bf0abf4
GitHub-Pull-Request: golang/crypto#82
Reviewed-by: Adam Langley <>
Reviewed-by: Brad Fitzpatrick <>
2 files changed