[Python-checkins] r46230 - python/trunk/Objects/stringobject.c

[fredrik.lundh]

Author: fredrik.lundh
Date: Thu May 25 19:55:31 2006
New Revision: 46230

Modified:
   python/trunk/Objects/stringobject.c
Log:
needforspeed: use "fastsearch" for count.  this results in a 3x speedup
for the related stringbench tests.



Modified: python/trunk/Objects/stringobject.c
==============================================================================
--- python/trunk/Objects/stringobject.c	(original)
+++ python/trunk/Objects/stringobject.c	Thu May 25 19:55:31 2006
@@ -5,6 +5,18 @@
 
 #include <ctype.h>
 
+#undef USE_INLINE /* XXX - set via configure? */
+
+#if defined(_MSC_VER) /* this is taken from _sre.c */
+#pragma warning(disable: 4710)
+/* fastest possible local call under MSVC */
+#define LOCAL(type) static __inline type __fastcall
+#elif defined(USE_INLINE)
+#define LOCAL(type) static inline type
+#else
+#define LOCAL(type) static type
+#endif
+
 #ifdef COUNT_ALLOCS
 int null_strings, one_strings;
 #endif
@@ -763,6 +775,108 @@
 	return 0;
 }
 
+/* -------------------------------------------------------------------- */
+/* Helpers */
+
+#define USE_FAST /* experimental fast search implementation */
+
+/* XXX - this code is copied from unicodeobject.c.  we really should
+   refactor the core implementations (see _sre.c for how this can be
+   done), but that'll have to wait -- fredrik */
+
+/* fast search/count implementation, based on a mix between boyer-
+   moore and horspool, with a few more bells and whistles on the top.
+   for some more background, see: http://effbot.org/stringlib */
+
+/* note: fastsearch may access s[n], which isn't a problem when using
+   Python's ordinary string types, but may cause problems if you're
+   using this code in other contexts.  also, the count mode returns -1
+   if there cannot possible be a match in the target string, and 0 if
+   it has actually checked for matches, but didn't find any.  callers
+   beware! */
+
+#define FAST_COUNT 0
+#define FAST_SEARCH 1
+
+LOCAL(Py_ssize_t)
+	fastsearch(const unsigned char* s, Py_ssize_t n, const unsigned char* p,
+		   Py_ssize_t m, int mode)
+{
+	long mask;
+	int skip, count = 0;
+	Py_ssize_t i, j, mlast, w;
+
+	w = n - m;
+
+	if (w < 0)
+		return -1;
+
+	/* look for special cases */
+	if (m <= 1) {
+		if (m <= 0)
+			return -1;
+		/* use special case for 1-character strings */
+		if (mode == FAST_COUNT) {
+			for (i = 0; i < n; i++)
+				if (s[i] == p[0])
+					count++;
+			return count;
+		} else {
+			for (i = 0; i < n; i++)
+				if (s[i] == p[0])
+					return i;
+		}
+		return -1;
+	}
+
+	mlast = m - 1;
+
+	/* create compressed boyer-moore delta 1 table */
+	skip = mlast - 1;
+	/* process pattern[:-1] */
+	for (mask = i = 0; i < mlast; i++) {
+		mask |= (1 << (p[i] & 0x1F));
+		if (p[i] == p[mlast])
+			skip = mlast - i - 1;
+	}
+	/* process pattern[-1] outside the loop */
+	mask |= (1 << (p[mlast] & 0x1F));
+
+	for (i = 0; i <= w; i++) {
+		/* note: using mlast in the skip path slows things down on x86 */
+		if (s[i+m-1] == p[m-1]) {
+			/* candidate match */
+			for (j = 0; j < mlast; j++)
+				if (s[i+j] != p[j])
+					break;
+			if (j == mlast) {
+				/* got a match! */
+				if (mode != FAST_COUNT)
+					return i;
+				count++;
+				i = i + mlast;
+				continue;
+			}
+			/* miss: check if next character is part of pattern */
+			if (!(mask & (1 << (s[i+m] & 0x1F))))
+				i = i + m;
+			else {
+				i = i + skip;
+				continue;
+			}
+		} else {
+			/* skip: check if next character is part of pattern */
+			if (!(mask & (1 << (s[i+m] & 0x1F))))
+				i = i + m;
+		}
+	}
+
+	if (mode != FAST_COUNT)
+		return -1;
+	return count;
+}
+
+/* -------------------------------------------------------------------- */
 /* Methods */
 
 static int
@@ -2177,7 +2291,7 @@
 static PyObject *
 string_count(PyStringObject *self, PyObject *args)
 {
-	const char *s = PyString_AS_STRING(self), *sub, *t;
+	const char *s = PyString_AS_STRING(self), *sub;
 	Py_ssize_t len = PyString_GET_SIZE(self), n;
 	Py_ssize_t i = 0, last = PY_SSIZE_T_MAX;
 	Py_ssize_t m, r;
@@ -2210,8 +2324,14 @@
 	if (n == 0)
 		return PyInt_FromSsize_t(m-i);
 
+#ifdef USE_FAST
+	r = fastsearch(s + i, last - i, sub, n, FAST_COUNT);
+	if (r < 0)
+		r = 0; /* no match */
+#else
 	r = 0;
 	while (i < m) {
+		const char *t
 		if (!memcmp(s+i, sub, n)) {
 			r++;
 			i += n;
@@ -2225,6 +2345,7 @@
 			break;
 		i = t - s;
 	}
+#endif
 	return PyInt_FromSsize_t(r);
 }