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gh-155555: str.find equal length fast path #155556

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impl
dg-pb Aug 11, 2026
18df541
📜🤖 Added by blurb_it.
blurb-it[bot] Aug 11, 2026
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-08-11-13-21-02.gh-issue-155555.CYo1PR.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
String search is now up to to 20x faster when string and pattern are of the same size.
9 changes: 9 additions & 0 deletions Objects/stringlib/fastsearch.h
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Original file line number Diff line number Diff line change
Expand Up @@ -795,6 +795,15 @@ FASTSEARCH(const STRINGLIB_CHAR* s, Py_ssize_t n,
return STRINGLIB(count_char)(s, n, p[0], maxcount);
}
}
else if (n == m) {
/* use special case when both strings are of equal length */
int res = memcmp(s, p, m * sizeof(STRINGLIB_CHAR));
if (mode == FAST_COUNT){
return res == 0 ? 1 : 0;
} else {
return res == 0 ? 0 : -1;
}
}

if (mode != FAST_RSEARCH) {
if (n < 2500 || (m < 100 && n < 30000) || m < 6) {
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