Depending on whether this code is in a hotpath (and considering how "elementary" it is, I figure that's a possibility), this could very well be a significant speed improvement.

Though I'd say that only excuses it if it's truly an elementary function (and not one line as part of a larger function), as otherwise it's unreadable garbage. But on its own it:

• has a clear purpose
• (presumably) isn't reimplementing functionality
• is easily tested
• can be modified with no side effects (besides breaking your calendar, but that's beside the point)