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author | Tim Peters <tim.peters@gmail.com> | 2022-01-25 01:06:00 (GMT) |
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committer | GitHub <noreply@github.com> | 2022-01-25 01:06:00 (GMT) |
commit | 7c26472d09548905d8c158b26b6a2b12de6cdc32 (patch) | |
tree | 282ffe1c879e53091e01aa2bd4bce7c7d1f369dd /Objects | |
parent | b18fd54f8c27e4b2aac222e75ac58aa85e5a7988 (diff) | |
download | cpython-7c26472d09548905d8c158b26b6a2b12de6cdc32.zip cpython-7c26472d09548905d8c158b26b6a2b12de6cdc32.tar.gz cpython-7c26472d09548905d8c158b26b6a2b12de6cdc32.tar.bz2 |
bpo-46504: faster code for trial quotient in x_divrem() (GH-30856)
* bpo-46504: faster code for trial quotient in x_divrem()
This brings x_divrem() back into synch with x_divrem1(), which was changed
in bpo-46406 to generate faster code to find machine-word division
quotients and remainders. Modern processors compute both with a single
machine instruction, but convincing C to exploit that requires writing
_less_ "clever" C code.
Diffstat (limited to 'Objects')
-rw-r--r-- | Objects/longobject.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/Objects/longobject.c b/Objects/longobject.c index ee20e26..5f0cc57 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -2767,8 +2767,15 @@ x_divrem(PyLongObject *v1, PyLongObject *w1, PyLongObject **prem) vtop = vk[size_w]; assert(vtop <= wm1); vv = ((twodigits)vtop << PyLong_SHIFT) | vk[size_w-1]; + /* The code used to compute the remainder via + * r = (digit)(vv - (twodigits)wm1 * q); + * and compilers generally generated code to do the * and -. + * But modern processors generally compute q and r with a single + * instruction, and modern optimizing compilers exploit that if we + * _don't_ try to optimize it. + */ q = (digit)(vv / wm1); - r = (digit)(vv - (twodigits)wm1 * q); /* r = vv % wm1 */ + r = (digit)(vv % wm1); while ((twodigits)wm2 * q > (((twodigits)r << PyLong_SHIFT) | vk[size_w-2])) { --q; |