From e2cef885a25967605007248cb158671b765df002 Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sat, 13 Apr 2013 22:45:04 +0300
Subject: Issue #16061: Speed up str.replace() for replacing 1-character
 strings.

---
 Objects/stringlib/replace.h | 53 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 Objects/stringlib/replace.h

(limited to 'Objects/stringlib/replace.h')

diff --git a/Objects/stringlib/replace.h b/Objects/stringlib/replace.h
new file mode 100644
index 00000000000..ef318ed6dd5
--- /dev/null
+++ b/Objects/stringlib/replace.h
@@ -0,0 +1,53 @@
+/* stringlib: replace implementation */
+
+#ifndef STRINGLIB_FASTSEARCH_H
+#error must include "stringlib/fastsearch.h" before including this module
+#endif
+
+Py_LOCAL_INLINE(void)
+STRINGLIB(replace_1char_inplace)(STRINGLIB_CHAR* s, STRINGLIB_CHAR* end,
+                                 Py_UCS4 u1, Py_UCS4 u2, Py_ssize_t maxcount)
+{
+    *s = u2;
+    while (--maxcount && ++s != end) {
+        /* Find the next character to be replaced.
+
+           If it occurs often, it is faster to scan for it using an inline
+           loop.  If it occurs seldom, it is faster to scan for it using a
+           function call; the overhead of the function call is amortized
+           across the many characters that call covers.  We start with an
+           inline loop and use a heuristic to determine whether to fall back
+           to a function call. */
+        if (*s != u1) {
+            int attempts = 10;
+            /* search u1 in a dummy loop */
+            while (1) {
+                if (++s == end)
+                    return;
+                if (*s == u1)
+                    break;
+                if (!--attempts) {
+                    /* if u1 was not found for attempts iterations,
+                       use FASTSEARCH() or memchr() */
+#if STRINGLIB_SIZEOF_CHAR == 1
+                    s++;
+                    s = memchr(s, u1, end - s);
+                    if (s == NULL)
+                        return;
+#else
+                    Py_ssize_t i;
+                    STRINGLIB_CHAR ch1 = (STRINGLIB_CHAR) u1;
+                    s++;
+                    i = FASTSEARCH(s, end - s, &ch1, 1, 0, FAST_SEARCH);
+                    if (i < 0)
+                        return;
+                    s += i;
+#endif
+                    /* restart the dummy loop */
+                    break;
+                }
+            }
+        }
+        *s = u2;
+    }
+}
-- 
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