needforspeed: new replace implementation by Andrew Dalke. replace is

now about 3x faster on my machine, for the replace tests from string-
bench.

1 files changed, 605 insertions, 182 deletions

diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index 77796df..aed0c23 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -2379,175 +2379,623 @@ string_translate(PyStringObject *self, PyObject *args)
 }
 
 
-/* What follows is used for implementing replace().  Perry Stoll. */
+#define FORWARD 1
+#define REVERSE -1
 
-/*
-  mymemfind
+/* find and count characters and substrings */
 
-  strstr replacement for arbitrary blocks of memory.
+/* Don't call if length < 2 */
+#define Py_STRING_MATCH(target, offset, pattern, length)	\
+  (target[offset] == pattern[0] &&				\
+   target[offset+length-1] == pattern[length-1] &&		\
+   !memcmp(target+offset+1, pattern+1, length-2) )
+
+#define findchar(target, target_len, c)				\
+  ((char *)memchr((const void *)(target), c, target_len))
+
+/* String ops must return a string.  */
+/* If the object is subclass of string, create a copy */
+static PyStringObject *
+return_self(PyStringObject *self)
+{
+	if (PyString_CheckExact(self)) {
+		Py_INCREF(self);
+		return self;
+	}
+	return (PyStringObject *)PyString_FromStringAndSize(
+		PyString_AS_STRING(self),
+		PyString_GET_SIZE(self));
+}
 
-  Locates the first occurrence in the memory pointed to by MEM of the
-  contents of memory pointed to by PAT.  Returns the index into MEM if
-  found, or -1 if not found.  If len of PAT is greater than length of
-  MEM, the function returns -1.
-*/
 static Py_ssize_t
-mymemfind(const char *mem, Py_ssize_t len, const char *pat, Py_ssize_t pat_len)
+countchar(char *target, int target_len, char c)
 {
-	register Py_ssize_t ii;
+	Py_ssize_t count=0;
+	char *start=target;
+	char *end=target+target_len;
+
+	while ( (start=findchar(start, end-start, c)) != NULL ) {
+		count++;
+		start += 1;
+	}
 
-	/* pattern can not occur in the last pat_len-1 chars */
-	len -= pat_len;
+	return count;
+}
 
-	for (ii = 0; ii <= len; ii++) {
-		if (mem[ii] == pat[0] && memcmp(&mem[ii], pat, pat_len) == 0) {
-			return ii;
-		}
+static Py_ssize_t
+findstring(char *target, Py_ssize_t target_len,
+	   char *pattern, Py_ssize_t pattern_len,
+	   Py_ssize_t start,
+	   Py_ssize_t end,
+	   int direction)
+{
+	if (start < 0) {
+		start += target_len;
+		if (start < 0)
+			start = 0;
+	}
+	if (end > target_len) {
+		end = target_len;
+	} else if (end < 0) {
+		end += target_len;
+		if (end < 0)
+			end = 0;
+	}
+
+	/* zero-length substrings always match at the first attempt */
+	if (pattern_len == 0)
+		return (direction > 0) ? start : end;
+
+	end -= pattern_len;
+
+	if (direction < 0) {
+		for (; end >= start; end--)
+			if (Py_STRING_MATCH(target, end, pattern, pattern_len))
+				return end;
+	} else {
+		for (; start <= end; start++)
+			if (Py_STRING_MATCH(target, start, pattern, pattern_len))
+				return start;
 	}
 	return -1;
 }
 
-/*
-  mymemcnt
+Py_ssize_t
+countstring(char *target, Py_ssize_t target_len,
+	    char *pattern, Py_ssize_t pattern_len,
+	    Py_ssize_t start,
+	    Py_ssize_t end,
+	    int direction)
+{
+	Py_ssize_t count=0;
 
-   Return the number of distinct times PAT is found in MEM.
-   meaning mem=1111 and pat==11 returns 2.
-           mem=11111 and pat==11 also return 2.
- */
-static Py_ssize_t
-mymemcnt(const char *mem, Py_ssize_t len, const char *pat, Py_ssize_t pat_len)
+	if (start < 0) {
+		start += target_len;
+		if (start < 0)
+			start = 0;
+	}
+	if (end > target_len) {
+		end = target_len;
+	} else if (end < 0) {
+		end += target_len;
+		if (end < 0)
+			end = 0;
+	}
+
+	/* zero-length substrings match everywhere */
+	if (pattern_len == 0)
+		return target_len+1;
+
+	end -= pattern_len;
+
+	if (direction < 0) {
+		for (; end >= start; end--)
+			if (Py_STRING_MATCH(target, end, pattern, pattern_len)) {
+				count++;
+				end -= pattern_len-1;
+			}
+	} else {
+		for (; start <= end; start++)
+			if (Py_STRING_MATCH(target, start, pattern, pattern_len)) {
+				count++;
+				start += pattern_len-1;
+			}
+	}
+	return count;
+}
+
+
+/* Algorithms for difference cases of string replacement */
+
+/* len(self)>=1, from="", len(to)>=1, maxcount>=1 */
+static PyStringObject *
+replace_interleave(PyStringObject *self,
+		   PyStringObject *to,
+		   Py_ssize_t maxcount)
 {
-	register Py_ssize_t offset = 0;
-	Py_ssize_t nfound = 0;
+	char *self_s, *to_s, *result_s;
+	Py_ssize_t self_len, to_len, result_len;
+	Py_ssize_t count, i, product;
+	PyStringObject *result;
+
+	self_len = PyString_GET_SIZE(self);
+	to_len = PyString_GET_SIZE(to);
+	
+	/* 1 at the end plus 1 after every character */
+	count = self_len+1;
+	if (maxcount < count) 
+		count = maxcount;
+	
+	/* Check for overflow */
+	/*   result_len = count * to_len + self_len; */
+	product = count * to_len;
+	if (product / to_len != count) {
+		PyErr_SetString(PyExc_OverflowError,
+				"replace string is too long");
+		return NULL;
+	}
+	result_len = product + self_len;
+	if (result_len < 0) {
+		PyErr_SetString(PyExc_OverflowError,
+				"replace string is too long");
+		return NULL;
+	}
+  
+	if (! (result = (PyStringObject *)
+	                 PyString_FromStringAndSize(NULL, result_len)) )
+		return NULL;
 
-	while (len >= 0) {
-		offset = mymemfind(mem, len, pat, pat_len);
-		if (offset == -1)
-			break;
-		mem += offset + pat_len;
-		len -= offset + pat_len;
-		nfound++;
+	self_s = PyString_AS_STRING(self);
+	to_s = PyString_AS_STRING(to);
+	to_len = PyString_GET_SIZE(to);
+	result_s = PyString_AS_STRING(result);
+
+	/* TODO: special case single character, which doesn't need memcpy */
+
+	/* Lay the first one down (guaranteed this will occur) */
+	memcpy(result_s, to_s, to_len);
+	result_s += to_len;
+	count -= 1;
+  
+	for (i=0; i<count; i++) {
+		*result_s++ = *self_s++;
+		memcpy(result_s, to_s, to_len);
+		result_s += to_len;
 	}
-	return nfound;
+
+	/* Copy the rest of the original string */
+	memcpy(result_s, self_s, self_len-i);
+
+	return result;
 }
 
-/*
-   mymemreplace
+/* Special case for deleting a single character */
+/* len(self)>=1, len(from)==1, to="", maxcount>=1 */
+static PyStringObject *
+replace_delete_single_character(PyStringObject *self,
+				char from_c, Py_ssize_t maxcount)
+{
+	char *self_s, *result_s;
+	char *start, *next, *end;
+	Py_ssize_t self_len, result_len;
+	Py_ssize_t count;
+	PyStringObject *result;
+
+	self_len = PyString_GET_SIZE(self);
+	self_s = PyString_AS_STRING(self);
+
+	count = countchar(self_s, self_len, from_c);
+	if (count == 0) {
+		return return_self(self);
+	}
+	if (count > maxcount)
+		count = maxcount;
+  
+	result_len = self_len - count;  /* from_len == 1 */
+	assert(result_len>=0);
+
+	if ( (result = (PyStringObject *)
+	                PyString_FromStringAndSize(NULL, result_len)) == NULL)
+		return NULL;
+	result_s = PyString_AS_STRING(result);
 
-   Return a string in which all occurrences of PAT in memory STR are
-   replaced with SUB.
+	start = self_s;
+	end = self_s + self_len;
+	while (count-- > 0) {
+		next = findchar(start, end-start, from_c);
+		if (next == NULL)
+			break;
+		memcpy(result_s, start, next-start);
+		result_s += (next-start);
+		start = next+1;
+	}
+	memcpy(result_s, start, end-start);
+	
+	return result;
+}
 
-   If length of PAT is less than length of STR or there are no occurrences
-   of PAT in STR, then the original string is returned. Otherwise, a new
-   string is allocated here and returned.
+/* len(self)>=1, len(from)>=2, to="", maxcount>=1 */
+
+static PyStringObject *
+replace_delete_substring(PyStringObject *self, PyStringObject *from,
+			 Py_ssize_t maxcount) {
+	char *self_s, *from_s, *result_s;
+	char *start, *next, *end;
+	Py_ssize_t self_len, from_len, result_len;
+	Py_ssize_t count, offset;
+	PyStringObject *result;
+
+	self_len = PyString_GET_SIZE(self);
+	self_s = PyString_AS_STRING(self);
+	from_len = PyString_GET_SIZE(from);
+	from_s = PyString_AS_STRING(from);
+
+	count = countstring(self_s, self_len,
+			    from_s, from_len,
+			    0, self_len, 1);
+  
+	if (count > maxcount)
+		count = maxcount;
+
+	if (count == 0) {
+		/* no matches */
+		return return_self(self);
+	}
+
+	result_len = self_len - (count * from_len);
+	assert (result_len>=0);
+	
+	if ( (result = (PyStringObject *)
+	      PyString_FromStringAndSize(NULL, result_len)) == NULL )
+		return NULL;
+	
+	result_s = PyString_AS_STRING(result);
+	
+	start = self_s;
+	end = self_s + self_len;
+	while (count-- > 0) {
+		offset = findstring(start, end-start,
+				    from_s, from_len,
+				    0, end-start, FORWARD);
+		if (offset == -1)
+			break;
+		next = start + offset;
+		
+		memcpy(result_s, start, next-start);
+		
+		result_s += (next-start);
+		start = next+from_len;
+	}
+	memcpy(result_s, start, end-start);
+	return result;
+}
 
-   on return, out_len is:
-       the length of output string, or
-       -1 if the input string is returned, or
-       unchanged if an error occurs (no memory).
+/* len(self)>=1, len(from)==len(to)==1, maxcount>=1 */
+static PyStringObject *
+replace_single_character_in_place(PyStringObject *self,
+				  char from_c, char to_c,
+				  Py_ssize_t maxcount)
+{
+	char *self_s, *result_s, *start, *end, *next;
+	Py_ssize_t self_len;
+	PyStringObject *result;
+	
+	/* The result string will be the same size */
+	self_s = PyString_AS_STRING(self);
+	self_len = PyString_GET_SIZE(self);
+	
+	next = findchar(self_s, self_len, from_c);
+	
+	if (next == NULL) {
+		/* No matches; return the original string */
+		return return_self(self);
+	}
+	
+	/* Need to make a new string */
+	result = (PyStringObject *) PyString_FromStringAndSize(self_s, self_len);
+	if (result == NULL)
+		return NULL;
+	result_s = PyString_AS_STRING(result);
+	
+	/* change everything in-place, starting with this one */
+	start =  result_s + (next-self_s);
+	*start = to_c;
+	start++;
+	end = result_s + self_len;
+	
+	while (--maxcount > 0) {
+		next = findchar(start, end-start, from_c);
+		if (next == NULL)
+			break;
+		*next = to_c;
+		start = next+1;
+	}
+	
+	return result;
+}
 
-   return value is:
-       the new string allocated locally, or
-       NULL if an error occurred.
-*/
-static char *
-mymemreplace(const char *str, Py_ssize_t len,		/* input string */
-             const char *pat, Py_ssize_t pat_len,	/* pattern string to find */
-             const char *sub, Py_ssize_t sub_len,	/* substitution string */
-             Py_ssize_t count,				/* number of replacements */
-	     Py_ssize_t *out_len)
+/* len(self)>=1, len(from)==len(to)>=2, maxcount>=1 */
+static PyStringObject *
+replace_substring_in_place(PyStringObject *self,
+			   PyStringObject *from,
+			   PyStringObject *to,
+			   Py_ssize_t maxcount)
 {
-	char *out_s;
-	char *new_s;
-	Py_ssize_t nfound, offset, new_len;
-        Py_ssize_t product, delta;
-
-	if (len == 0 || (pat_len == 0 && sub_len == 0) || pat_len > len)
-		goto return_same;
-
-	/* find length of output string */
-	nfound = (pat_len > 0) ? mymemcnt(str, len, pat, pat_len) : len + 1;
-	if (count < 0)
-		count = PY_SSIZE_T_MAX;
-	else if (nfound > count)
-		nfound = count;
-	if (nfound == 0)
-		goto return_same;
-
-        delta = (sub_len - pat_len);
-        if (delta == 0) {
-            new_len = len;
-        } else {
-            product = nfound * (sub_len - pat_len);
-            if ((product / (sub_len - pat_len)) != nfound) {
-                PyErr_SetString(PyExc_OverflowError,
-                                "replace string is too long");
-                return NULL;
-            }
-            new_len = len + product;
-            if (new_len < 0) {
-                PyErr_SetString(PyExc_OverflowError,
-                                "replace string is too long");
-                return NULL;
-            }
-        }
+	char *result_s, *start, *end;
+	char *self_s, *from_s, *to_s;
+	Py_ssize_t self_len, from_len, offset;
+	PyStringObject *result;
+	
+	/* The result string will be the same size */
+	
+	self_s = PyString_AS_STRING(self);
+	self_len = PyString_GET_SIZE(self);
+	
+	from_s = PyString_AS_STRING(from);
+	from_len = PyString_GET_SIZE(from);
+	to_s = PyString_AS_STRING(to);
+	
+	offset = findstring(self_s, self_len,
+			    from_s, from_len,
+			    0, self_len, FORWARD);
+	
+	if (offset == -1) {
+		/* No matches; return the original string */
+		return return_self(self);
+	}
+	
+	/* Need to make a new string */
+	result = (PyStringObject *) PyString_FromStringAndSize(self_s, self_len);
+	if (result == NULL)
+		return NULL;
+	result_s = PyString_AS_STRING(result);
+	
+	/* change everything in-place, starting with this one */
+	start =  result_s + offset;
+	memcpy(start, to_s, from_len);
+	start += from_len;
+	end = result_s + self_len;
+	
+	while ( --maxcount > 0) {
+		offset = findstring(start, end-start,
+				    from_s, from_len,
+				    0, end-start, FORWARD);
+		if (offset==-1)
+			break;
+		memcpy(start+offset, to_s, from_len);
+		start += offset+from_len;
+	}
+	
+	return result;
+}
 
-	if (new_len == 0) {
-		/* Have to allocate something for the caller to free(). */
-		out_s = (char *)PyMem_MALLOC(1);
-		if (out_s == NULL)
-			return NULL;
-		out_s[0] = '\0';
+/* len(self)>=1, len(from)==1, len(to)>=2, maxcount>=1 */
+static PyStringObject *
+replace_single_character(PyStringObject *self,
+			 char from_c,
+			 PyStringObject *to,
+			 Py_ssize_t maxcount)
+{
+	char *self_s, *to_s, *result_s;
+	char *start, *next, *end;
+	Py_ssize_t self_len, to_len, result_len;
+	Py_ssize_t count, product;
+	PyStringObject *result;
+	
+	self_s = PyString_AS_STRING(self);
+	self_len = PyString_GET_SIZE(self);
+	
+	count = countchar(self_s, self_len, from_c);
+	if (count > maxcount)
+		count = maxcount;
+	
+	if (count == 0) {
+		/* no matches, return unchanged */
+		return return_self(self);
+	}
+	
+	to_s = PyString_AS_STRING(to);
+	to_len = PyString_GET_SIZE(to);
+	
+	/* use the difference between current and new, hence the "-1" */
+	/*   result_len = self_len + count * (to_len-1)  */
+	product = count * (to_len-1);
+	if (product / (to_len-1) != count) {
+		PyErr_SetString(PyExc_OverflowError, "replace string is too long");
+		return NULL;
 	}
-	else {
-		assert(new_len > 0);
-		new_s = (char *)PyMem_MALLOC(new_len);
-		if (new_s == NULL)
-			return NULL;
-		out_s = new_s;
-
-		if (pat_len > 0) {
-			for (; nfound > 0; --nfound) {
-				/* find index of next instance of pattern */
-				offset = mymemfind(str, len, pat, pat_len);
-				if (offset == -1)
-					break;
-
-				/* copy non matching part of input string */
-				memcpy(new_s, str, offset);
-				str += offset + pat_len;
-				len -= offset + pat_len;
-
-				/* copy substitute into the output string */
-				new_s += offset;
-				memcpy(new_s, sub, sub_len);
-				new_s += sub_len;
-			}
-			/* copy any remaining values into output string */
-			if (len > 0)
-				memcpy(new_s, str, len);
-		}
-		else {
-			for (;;++str, --len) {
-				memcpy(new_s, sub, sub_len);
-				new_s += sub_len;
-				if (--nfound <= 0) {
-					memcpy(new_s, str, len);
-					break;
-				}
-				*new_s++ = *str;
-			}
+	result_len = self_len + product;
+	if (result_len < 0) {
+		PyErr_SetString(PyExc_OverflowError, "replace string is too long");
+		return NULL;
+	}
+	
+	if ( (result = (PyStringObject *)
+	      PyString_FromStringAndSize(NULL, result_len)) == NULL)
+		return NULL;
+	result_s = PyString_AS_STRING(result);
+	
+	start = self_s;
+	end = self_s + self_len;
+	while (count-- > 0) {
+		next = findchar(start, end-start, from_c);
+		if (next == NULL) 
+			break;
+		
+		if (next == start) {
+			/* replace with the 'to' */
+			memcpy(result_s, to_s, to_len);
+			result_s += to_len;
+			start += 1;
+		} else {
+			/* copy the unchanged old then the 'to' */
+			memcpy(result_s, start, next-start);
+			result_s += (next-start);
+			memcpy(result_s, to_s, to_len);
+			result_s += to_len;
+			start = next+1;
 		}
 	}
-	*out_len = new_len;
-	return out_s;
+	/* Copy the remainder of the remaining string */
+	memcpy(result_s, start, end-start);
+	
+	return result;
+}
 
-  return_same:
-	*out_len = -1;
-	return (char *)str; /* cast away const */
+/* len(self)>=1, len(from)>=2, len(to)>=2, maxcount>=1 */
+static PyStringObject *
+replace_substring(PyStringObject *self,
+		  PyStringObject *from,
+		  PyStringObject *to,
+		  Py_ssize_t maxcount) {
+	char *self_s, *from_s, *to_s, *result_s;
+	char *start, *next, *end;
+	Py_ssize_t self_len, from_len, to_len, result_len;
+	Py_ssize_t count, offset, product;
+	PyStringObject *result;
+	
+	self_s = PyString_AS_STRING(self);
+	self_len = PyString_GET_SIZE(self);
+	from_s = PyString_AS_STRING(from);
+	from_len = PyString_GET_SIZE(from);
+	
+	count = countstring(self_s, self_len,
+			    from_s, from_len,
+			    0, self_len, FORWARD);
+	if (count > maxcount)
+		count = maxcount;
+	
+	if (count == 0) {
+		/* no matches, return unchanged */
+		return return_self(self);
+	}
+	
+	to_s = PyString_AS_STRING(to);
+	to_len = PyString_GET_SIZE(to);
+	
+	/* Check for overflow */
+	/*    result_len = self_len + count * (to_len-from_len) */
+	product = count * (to_len-from_len);
+	if (product / (to_len-from_len) != count) {
+		PyErr_SetString(PyExc_OverflowError, "replace string is too long");
+		return NULL;
+	}
+	result_len = self_len + product;
+	if (result_len < 0) {
+		PyErr_SetString(PyExc_OverflowError, "replace string is too long");
+		return NULL;
+	}
+	
+	if ( (result = (PyStringObject *)
+	      PyString_FromStringAndSize(NULL, result_len)) == NULL)
+		return NULL;
+	result_s = PyString_AS_STRING(result);
+	
+	start = self_s;
+	end = self_s + self_len;
+	while (count-- > 0) {
+		offset = findstring(start, end-start,
+				    from_s, from_len,
+				    0, end-start, FORWARD);
+		if (offset == -1)
+			break;
+		next = start+offset;
+		if (next == start) {
+			/* replace with the 'to' */
+			memcpy(result_s, to_s, to_len);
+			result_s += to_len;
+			start += from_len;
+		} else {
+			/* copy the unchanged old then the 'to' */
+			memcpy(result_s, start, next-start);
+			result_s += (next-start);
+			memcpy(result_s, to_s, to_len);
+			result_s += to_len;
+			start = next+from_len;
+		}
+	}
+	/* Copy the remainder of the remaining string */
+	memcpy(result_s, start, end-start);
+	
+	return result;
 }
 
 
+static PyStringObject *
+replace(PyStringObject *self,
+	PyStringObject *from,
+	PyStringObject *to,
+	Py_ssize_t maxcount)
+{
+	Py_ssize_t from_len, to_len;
+	
+	if (maxcount < 0) {
+		maxcount = PY_SSIZE_T_MAX;
+	} else if (maxcount == 0 || PyString_GET_SIZE(self) == 0) {
+		/* nothing to do; return the original string */
+		return return_self(self);
+	}
+	
+	from_len = PyString_GET_SIZE(from);
+	to_len = PyString_GET_SIZE(to);
+	
+	if (maxcount == 0 ||
+	    (from_len == 0 && to_len == 0)) {
+		/* nothing to do; return the original string */
+		return return_self(self);
+	}
+
+	/* Handle zero-length special cases */
+	
+	if (from_len == 0) {
+		/* insert the 'to' string everywhere.   */
+		/*    >>> "Python".replace("", ".")     */
+		/*    '.P.y.t.h.o.n.'                   */
+		return replace_interleave(self, to, maxcount);
+	}
+
+	/* Except for "".replace("", "A") == "A" there is no way beyond this */
+	/* point for an empty self string to generate a non-empty string */
+	/* Special case so the remaining code always gets a non-empty string */
+	if (PyString_GET_SIZE(self) == 0) {
+		return return_self(self);
+	}
+
+	if (to_len == 0) {
+		/* delete all occurances of 'from' string */
+		if (from_len == 1) {
+			return replace_delete_single_character(
+				self, PyString_AS_STRING(from)[0], maxcount);
+		} else {
+			return replace_delete_substring(self, from, maxcount);
+		}
+	}
+
+	/* Handle special case where both strings have the same length */
+
+	if (from_len == to_len) {
+		if (from_len == 1) {
+			return replace_single_character_in_place(
+				self,
+				PyString_AS_STRING(from)[0],
+				PyString_AS_STRING(to)[0],
+				maxcount);
+		} else {
+			return replace_substring_in_place(
+				self, from, to, maxcount);
+		}
+	}
+
+	/* Otherwise use the more generic algorithms */
+	if (from_len == 1) {
+		return replace_single_character(self, PyString_AS_STRING(from)[0],
+						to, maxcount);
+	} else {
+		/* len('from')>=2, len('to')>=1 */
+		return replace_substring(self, from, to, maxcount);
+	}
+}
+
 PyDoc_STRVAR(replace__doc__,
 "S.replace (old, new[, count]) -> string\n\
 \n\
@@ -2558,67 +3006,42 @@ given, only the first count occurrences are replaced.");
 static PyObject *
 string_replace(PyStringObject *self, PyObject *args)
 {
-	const char *str = PyString_AS_STRING(self), *sub, *repl;
-	char *new_s;
-	const Py_ssize_t len = PyString_GET_SIZE(self);
-	Py_ssize_t sub_len, repl_len, out_len;
 	Py_ssize_t count = -1;
-	PyObject *newobj;
-	PyObject *subobj, *replobj;
+	PyObject *from, *to;
+	char *tmp_s;
+	Py_ssize_t tmp_len;
 
-	if (!PyArg_ParseTuple(args, "OO|n:replace",
-			      &subobj, &replobj, &count))
+	if (!PyArg_ParseTuple(args, "OO|n:replace", &from, &to, &count))
 		return NULL;
 
-	if (PyString_Check(subobj)) {
-		sub = PyString_AS_STRING(subobj);
-		sub_len = PyString_GET_SIZE(subobj);
+	if (PyString_Check(from)) {
+	  /* Can this be made a '!check' after the Unicode check? */
 	}
 #ifdef Py_USING_UNICODE
-	else if (PyUnicode_Check(subobj))
+	if (PyUnicode_Check(from))
 		return PyUnicode_Replace((PyObject *)self,
-					 subobj, replobj, count);
+					 from, to, count);
 #endif
-	else if (PyObject_AsCharBuffer(subobj, &sub, &sub_len))
+	else if (PyObject_AsCharBuffer(from, &tmp_s, &tmp_len))
 		return NULL;
 
-	if (PyString_Check(replobj)) {
-		repl = PyString_AS_STRING(replobj);
-		repl_len = PyString_GET_SIZE(replobj);
+	if (PyString_Check(to)) {
+	  /* Can this be made a '!check' after the Unicode check? */
 	}
 #ifdef Py_USING_UNICODE
-	else if (PyUnicode_Check(replobj))
+	else if (PyUnicode_Check(to))
 		return PyUnicode_Replace((PyObject *)self,
-					 subobj, replobj, count);
+					 from, to, count);
 #endif
-	else if (PyObject_AsCharBuffer(replobj, &repl, &repl_len))
+	else if (PyObject_AsCharBuffer(to, &tmp_s, &tmp_len))
 		return NULL;
 
-	new_s = mymemreplace(str,len,sub,sub_len,repl,repl_len,count,&out_len);
-	if (new_s == NULL) {
-		if (!PyErr_Occurred())
-			PyErr_NoMemory();
-		return NULL;
-	}
-	if (out_len == -1) {
-		if (PyString_CheckExact(self)) {
-			/* we're returning another reference to self */
-			newobj = (PyObject*)self;
-			Py_INCREF(newobj);
-		}
-		else {
-			newobj = PyString_FromStringAndSize(str, len);
-			if (newobj == NULL)
-				return NULL;
-		}
-	}
-	else {
-		newobj = PyString_FromStringAndSize(new_s, out_len);
-		PyMem_FREE(new_s);
-	}
-	return newobj;
+	return (PyObject *)replace((PyStringObject *) self,
+				   (PyStringObject *) from,
+				   (PyStringObject *) to, count);
 }
 
+/** End DALKE **/
 
 PyDoc_STRVAR(startswith__doc__,
 "S.startswith(prefix[, start[, end]]) -> bool\n\