Replaced possibleSimpleKeys associative array in Scanner with an

ordinary array, added a mixin to generate fast lookup tables for
character search, and used said mixin in the greatest
bottlenecks. Another great speedup, at least 20%, can't keep
track of it anymore.

dyaml/fastcharsearch.d

@@ -0,0 +1,102 @@
+
+//          Copyright Ferdinand Majerech 2011.
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          http://www.boost.org/LICENSE_1_0.txt)
+
+module dyaml.fastcharsearch;
+
+
+import std.algorithm;
+import std.conv;
+
+
+package:
+
+/**
+ * Mixin used for fast searching for a character in string.
+ *
+ * Creates a lookup table to quickly determine if a character
+ * is present in the string. Size of the lookup table is limited;
+ * any characters not represented in the table will be checked
+ * by ordinary equality comparison.
+ *
+ * Params:  chars     = String to search in.
+ *          tableSize = Maximum number of bytes used by the table.
+ *
+ * Generated method: 
+ *     bool canFind(dchar c)
+ *
+ *     Determines if a character is in the string.
+ */
+template FastCharSearch(dstring chars, uint tableSize = 256)
+{
+    private mixin(searchCode!(chars, tableSize)());
+}
+
+///Generate the search table and the canFind method.
+string searchCode(dstring chars, uint tableSize)() 
+{
+    const tableSizeStr = to!string(tableSize);
+    ubyte[tableSize] table;
+    table[] = 0;
+
+    //Characters that don't fit in the table.
+    dchar[] specialChars;
+
+    foreach(c; chars)
+    {
+        if(c < tableSize){table[c] = 1;}
+        else             {specialChars ~= c;}
+    }
+
+    string tableCode()
+    {
+        string code = "static immutable ubyte table_[" ~ tableSizeStr ~ "] = [\n";
+        foreach(c; table[0 .. $ - 1])
+        {
+            code ~= c ? "true,\n" : "false,\n";
+        }
+        code ~= table[$ - 1] ? "true\n" : "false\n";
+        code ~= "];\n\n";
+        return code;
+    }
+
+    string specialCharsCode()
+    {
+        string code;
+        foreach(c; specialChars[0 .. $ - 1])
+        {
+            code ~= "cast(uint)c == " ~ to!string(cast(uint)c) ~ " || ";
+        }
+        code ~= "cast(uint)c == " ~ to!string(cast(uint)specialChars[$ - 1]);
+
+        return code;
+    }
+
+    string code = tableSize ? tableCode() : "";
+
+    code ~= "bool canFind(in dchar c) pure\n"
+            "{\n";
+
+    if(tableSize)
+    {
+        code ~= specialChars.length 
+                ?
+                "    if(c < " ~ tableSizeStr ~ ")\n"
+                "    {\n"
+                "        return cast(bool)table_[c];\n"
+                "    }\n"
+                :
+                "    return cast(bool)table_[c];\n";
+    }
+    if(specialChars.length)
+    {
+        code ~= "    return " ~ specialCharsCode() ~ ";\n";
+    }
+
+    code ~= "    assert(false);\n"
+            "}\n";
+
+    return code;
+}