needforspeed: stringlib refactoring (in progress)

2 files changed, 102 insertions, 0 deletions

diff --git a/Objects/stringlib/README.txt b/Objects/stringlib/README.txt
new file mode 100644
index 0000000..051197c
--- /dev/null
+++ b/Objects/stringlib/README.txt
@@ -0,0 +1,5 @@
+bits shared by the stringobject and unicodeobject implementations (and
+possibly other modules, in a not too distant future).
+
+the stuff in here is included into relevant places; see the individual
+source files for details.
diff --git a/Objects/stringlib/fastsearch.h b/Objects/stringlib/fastsearch.h
new file mode 100644
index 0000000..1ce7f13
--- /dev/null
+++ b/Objects/stringlib/fastsearch.h
@@ -0,0 +1,97 @@
+/* stringlib: fastsearch implementation */
+
+#ifndef STRINGLIB_FASTSEARCH_H
+#define STRINGLIB_FASTSEARCH_H
+
+/* 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
+
+Py_LOCAL(Py_ssize_t)
+fastsearch(const STRINGLIB_CHAR* s, Py_ssize_t n,
+           const STRINGLIB_CHAR* p, Py_ssize_t m,
+           int mode)
+{
+    long mask;
+    Py_ssize_t 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;
+        } 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;
+}
+
+#endif