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gh-129149: Add Missing fast path in PYLONG_FROM_UINT macro for compact integers#129168

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Merged
vstinner merged 21 commits into from
Jan 23, 2025
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gh-129149: Add Missing fast path in PYLONG_FROM_UINT macro for compact integers #129168

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ed9be47
Add Missing fast path in PyLong_From*() functions for compact integers
srinivasreddy Jan 22, 2025
ba70518
Revert change
srinivasreddy Jan 22, 2025
34315cb
Correct types
srinivasreddy Jan 22, 2025
0ef383c
Convert PyLong_FromLongLong() as well to leverage macro PYLONG_FROM_S…
srinivasreddy Jan 22, 2025
c00ba8c
Update Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issu…
srinivasreddy Jan 22, 2025
2b5163f
Update Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issu…
srinivasreddy Jan 22, 2025
955bb37
Update Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issu…
skirpichev Jan 22, 2025
237b8b9
Update Objects/longobject.c
srinivasreddy Jan 22, 2025
11ad06f
Move back PYLONG_FROM_UINT where it belongs earlier
srinivasreddy Jan 22, 2025
c25b910
Undo the changes
srinivasreddy Jan 22, 2025
37a5c9a
Updated blurb accordingly
srinivasreddy Jan 22, 2025
2cb1aec
Remove :c:macro since it is only internal macro
srinivasreddy Jan 22, 2025
99c5420
Address review comments
srinivasreddy Jan 22, 2025
2724758
Revert the refactoring
srinivasreddy Jan 23, 2025
2a8692d
Revert changes
srinivasreddy Jan 23, 2025
70d85f1
update the blurb : Remove note about refactoring
srinivasreddy Jan 23, 2025
af410e0
Remove blurb
srinivasreddy Jan 23, 2025
5a9e201
Revert "Remove blurb"
srinivasreddy Jan 23, 2025
5760c95
Update news entry for better wording
srinivasreddy Jan 23, 2025
1f81b87
Update Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issu…
srinivasreddy Jan 23, 2025
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Update Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issu…
srinivasreddy Jan 23, 2025
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issue-129149.wAYu43.rst
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@@ -0,0 +1,2 @@
Add fast path for medium-size integers in :c:func:`PyLong_FromUnsignedLong`,
:c:func:`PyLong_FromUnsignedLongLong` and :c:func:`PyLong_FromSize_t`.
8 changes: 6 additions & 2 deletions Objects/longobject.c
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Expand Up@@ -359,9 +359,13 @@ PyLong_FromLong(long ival)
if (IS_SMALL_UINT(ival)) { \
return get_small_int((sdigit)(ival)); \
} \
if ((ival) <= PyLong_MASK) { \
return _PyLong_FromMedium((sdigit)(ival)); \
} \
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skirpichev marked this conversation as resolved.
/* Do shift in two steps to avoid possible undefined behavior. */ \
INT_TYPE t = (ival) >> PyLong_SHIFT >> PyLong_SHIFT; \
/* Count the number of Python digits. */ \
Py_ssize_t ndigits = 0; \
INT_TYPE t = (ival); \
Py_ssize_t ndigits = 2; \

@eendebakpteendebakptJan 30, 2025

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Depending on the INT_TYPE the value of ndigits can only be 2 or 3. We can replace the while loop with a single if statement. E.g.

main...eendebakpt:cpython:fast_digit_count

@srinivasreddy Would you be interested in benchmarking this approach and making a PR?

@srinivasreddysrinivasreddyJan 31, 2025

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Yes. Absolutely.

@chris-eiblchris-eiblJan 31, 2025

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or 3

I do not think this works on a platform where e.g. long long is 128 bit? Or for PYLONG_BITS_IN_DIGIT=15 and long long being 64bit?
Maybe both hypothetical, but not impossible.

@eendebakpteendebakptJan 31, 2025

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Correct. We would need some guards for that. Whether that bit of complexity is worth is, depends on the benchmark results.

while (t) { \
++ndigits; \
t >>= PyLong_SHIFT; \
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