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

srinivasreddy · eendebakpt · skirpichev · web-flow · commit ab353b31bb30 · 2025-01-23T14:36:52.000Z
Add fast path in PyLong_From*() functions for compact integers.

Co-authored-by: Pieter Eendebak &lt;pieter.eendebak@gmail.com&gt;
Co-authored-by: Sergey B Kirpichev &lt;skirpichev@gmail.com&gt;
Co-authored-by: Yan Yanchii &lt;yyanchiy@gmail.com&gt;
Co-authored-by: Bénédikt Tran &lt;10796600+picnixz@users.noreply.github.com&gt;
Co-authored-by: Victor Stinner &lt;vstinner@python.org&gt;
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issue-129149.wAYu43.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-01-22-14-24-44.gh-issue-129149.wAYu43.rst
@@ -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`.
diff --git a/Objects/longobject.c b/Objects/longobject.c
@@ -365,9 +365,13 @@ PyLong_FromLong(long ival)
         if (IS_SMALL_UINT(ival)) { \
             return get_small_int((sdigit)(ival)); \
         } \
+        if ((ival) <= PyLong_MASK) { \
+            return _PyLong_FromMedium((sdigit)(ival)); \
+        } \
+        /* 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; \
         while (t) { \
             ++ndigits; \
             t >>= PyLong_SHIFT; \

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Add fast path for medium-size integers in :c:func:`PyLong_FromUnsignedLong`,
	`2`	+:c:func:`PyLong_FromUnsignedLongLong` and :c:func:`PyLong_FromSize_t`.