We seem to have ended up with redundant fast path checks for division in longobject.c: long_div has a fast path check, but the long_div slow path calls l_divmod, which then does a second, identical, fast path check. long_mod has similar behaviour. long_divmod, however, has no fast path, so relies on the one from l_divmod. This patch removes the extra fast path from l_divmod, and then adds a top-level fast path check to long_divmod.

N.B. The patch also tweaks the fast path condition to *include* the common case of a dividend of 0, and *exclude* the rare case of a negative divisor. (The latter change helps to keep the fast path code simple.)

Serhiy: thanks for the review. Replying here, since I get a 500 error every time I try to reply from Rietveld. I'd rather not rely on either NSMALLPOSINTS > 0 or on digit 0 existing when Py_SIZE is 0. We don't rely on that elsewhere, and the code should stay simple where possible.

The patch LGTM. I'll open separate issue for guaranteeing that a->ob_digit[0] is 0 in case of Py_SIZE(a) == 0 and using this fact for simplifying and optimizing the code.

What's the status of this?

> What's the status of this? Forgotten, rather than abandoned. :-( I'll unassign so that someone else can pick this up. I believe the patch is ready to go, except that of course now it needs a PR.