Hoist XTS mode check out of CipherContext update loop#15273
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CipherContext::update_into called back into Python with an is_instance(XTS) check on every 2^29-byte chunk of every update call, even though whether the mode is XTS is fixed at construction (where an identical check already runs). Store the result as a bool on the context and branch on that instead, removing a Python type lookup and isinstance call from the streaming cipher hot path. The py parameter to update_into existed only for that check, so it is dropped from the internal method and its callers. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XcTyprD7CsgzGHV9kEwksy
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This summary isn’t super accurate. When doing large chunks it calls once per 2**29, which is irrelevant, but it also calls once per update no matter what, which is inelegant and pointless. |
alex
approved these changes
Jul 17, 2026
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CipherContext::update_into called back into Python with an
is_instance(XTS) check on every 2^29-byte chunk of every update call,
even though whether the mode is XTS is fixed at construction (where an
identical check already runs). Store the result as a bool on the
context and branch on that instead, removing a Python type lookup and
isinstance call from the streaming cipher hot path.
The py parameter to update_into existed only for that check, so it is
dropped from the internal method and its callers.
Co-Authored-By: Claude Fable 5 noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01XcTyprD7CsgzGHV9kEwksy