Serhiy Storchaka added the comment: I adapted a patch to the current code (now it works for bytearrays too), deleted the behavior change, left optimization only for 0- and 1-bytes separator, deleted tests (bytes.join tests already exists), wrote a benchmark and after long experiments has set a condition for this optimization. Now, I believe, the patch never leads to regression. The patch has been simplified, it's only 13 lines long.
Thank you, John O'Connor. ---------- Added file: http://bugs.python.org/file27621/bytes_join_optimization_2.patch Added file: http://bugs.python.org/file27622/bytes_join_bench.sh _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue12805> _______________________________________
diff -r 5ae4ff03b35f Objects/stringlib/join.h
--- a/Objects/stringlib/join.h Thu Oct 18 22:18:42 2012 +0100
+++ b/Objects/stringlib/join.h Fri Oct 19 14:05:51 2012 +0300
@@ -94,6 +94,19 @@
/* Catenate everything. */
p = STRINGLIB_STR(res);
+ if (!seplen || (seplen == 1 && nbufs > 2 && nbufs > (sz >> 5))) {
+ /* fast path */
+ if (seplen)
+ memset(p + buffers[0].len, sepstr[0],
+ sz - buffers[0].len - buffers[nbufs - 1].len);
+ for (i = 0; i < nbufs; i++) {
+ Py_ssize_t n = buffers[i].len;
+ char *q = buffers[i].buf;
+ Py_MEMCPY(p, q, n);
+ p += n;
+ }
+ goto done;
+ }
for (i = 0; i < nbufs; i++) {
Py_ssize_t n;
char *q;
bytes_join_bench.sh
Description: application/shellscript
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