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gh-160872: Keep PyLong "x_divrem" inner loop carry in 64 bits #161156

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gh-160872: Keep PyLong "x_divrem" inner loop carry in 64 bits #161156

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gh-160872: Keep PyLong "x_divrem" inner loop carry in 64 bits
XiaohongGong Oct 29, 2026
562ff5a
📜🤖 Added by blurb_it.
blurb-it[bot] Nov 2, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-11-02-05-50-35.gh-issue-160872.x8NvzN.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Optimize division and remainder operations on large :class:`int` values.
12 changes: 5 additions & 7 deletions Objects/longobject.c
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Expand Up @@ -3325,8 +3325,7 @@ x_divrem(PyLongObject *v1, PyLongObject *w1, PyLongObject **prem)
int d;
digit wm1, wm2, carry, q, r, vtop, *v0, *vk, *w0, *ak;
twodigits vv;
sdigit zhi;
stwodigits z;
stwodigits z, zhi;

/* We follow Knuth [The Art of Computer Programming, Vol. 2 (3rd
edn.), section 4.3.1, Algorithm D], except that we don't explicitly
Expand Down Expand Up @@ -3416,16 +3415,15 @@ x_divrem(PyLongObject *v1, PyLongObject *w1, PyLongObject **prem)
for (i = 0; i < size_w; ++i) {
/* invariants: -PyLong_BASE <= -q <= zhi <= 0;
-PyLong_BASE * q <= z < PyLong_BASE */
z = (sdigit)vk[i] + zhi -
z = (stwodigits)vk[i] + zhi -
(stwodigits)q * (stwodigits)w0[i];
vk[i] = (digit)z & PyLong_MASK;
zhi = (sdigit)Py_ARITHMETIC_RIGHT_SHIFT(stwodigits,
z, PyLong_SHIFT);
zhi = Py_ARITHMETIC_RIGHT_SHIFT(stwodigits, z, PyLong_SHIFT);
}

/* add w back if q was too large (this branch taken rarely) */
assert((sdigit)vtop + zhi == -1 || (sdigit)vtop + zhi == 0);
if ((sdigit)vtop + zhi < 0) {
assert((stwodigits)vtop + zhi == -1 || (stwodigits)vtop + zhi == 0);
if ((stwodigits)vtop + zhi < 0) {
carry = 0;
for (i = 0; i < size_w; ++i) {
carry += vk[i] + w0[i];
Expand Down
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