https://github.com/python/cpython/commit/fc3cd8e3f59fcae208bc2b53014dcb90fdc038cb
commit: fc3cd8e3f59fcae208bc2b53014dcb90fdc038cb
branch: main
author: Victor Stinner <[email protected]>
committer: vstinner <[email protected]>
date: 2026-10-05T13:51:53+02:00
summary:
gh-158585: Optimize bytes.join() for non-empty separator (#158689)
Remove the conditional branch from the loop.
files:
M Objects/stringlib/join.h
diff --git a/Objects/stringlib/join.h b/Objects/stringlib/join.h
index fe460d41f6700f8..5fd2ca70f98dd31 100644
--- a/Objects/stringlib/join.h
+++ b/Objects/stringlib/join.h
@@ -134,13 +134,15 @@ STRINGLIB(bytes_join)(PyObject *sep, PyObject *iterable)
}
}
else {
- for (i = 0; i < nbufs; i++) {
- Py_ssize_t n;
- char *q;
- if (i) {
- memcpy(p, sepstr, seplen);
- p += seplen;
- }
+ Py_ssize_t n = buffers[0].len;
+ char *q = buffers[0].buf;
+ memcpy(p, q, n);
+ p += n;
+
+ for (i = 1; i < nbufs; i++) {
+ memcpy(p, sepstr, seplen);
+ p += seplen;
+
n = buffers[i].len;
q = buffers[i].buf;
memcpy(p, q, n);
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