On Jun 8, 2016 8:13 AM, "Paul Sokolovsky" <pmiscml at gmail.com> wrote: > > Hello, > > On Wed, 8 Jun 2016 14:45:22 +0300 > Serhiy Storchaka <storchaka at gmail.com> wrote: > > [] > > > > $ ./run-bench-tests bench/bytealloc* > > > bench/bytealloc: > > > 3.333s (+00.00%) bench/bytealloc-1-bytes_n.py > > > 11.244s (+237.35%) bench/bytealloc-2-repeat.py > > > > If the performance of creating an immutable array of n zero bytes is > > important in MicroPython, it is worth to optimize b"\0" * n. > > No matter how you optimize calloc + something, it's always slower than > just calloc. `bytes(n)` *is* calloc + something. It's a lookup of and call to a global function. (Unless MicroPython optimizes away lookups for builtins, in which case it can theoretically optimize b"\0".__mul__.) On the other hand, b"\0" is a constant, and * is an operator lookup that succeeds on the first argument (meaning, perhaps, a successful branch prediction). As a constant, it is only created once, so there's no intermediate object created. AFAICT, the first requires optimizing global function lookups + calls, and the second requires optimizing lookup and *successful* application of __mul__ (versus failure + fallback to some __rmul__), and repetitions of a particular `bytes` object (which can be interned and checked against). That means there is room for either to win, depending on the efforts of the implementers. (However, `bytearray` has no syntax for literals (and therefore easy constants), and is a more valid and, AFAIK, more practical concern.) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20160608/c6dfaeed/attachment.html>
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