faster fast grep

[Ted Unangst]

For simple patterns, grep has an optimization to avoid regex and run
about 50% faster. The problem is its idea of simple patterns is too
simple.

This diff switches the logic around from a whitelist to a blacklist. We
only need to abort the fast path if we see a magic regex character.

Index: util.c
===================================================================
RCS file: /cvs/src/usr.bin/grep/util.c,v
retrieving revision 1.45
diff -u -p -r1.45 util.c
--- util.c      29 Dec 2012 01:32:44 -0000      1.45
+++ util.c      1 May 2013 00:00:30 -0000
@@ -348,15 +348,8 @@ fastcomp(fastgrep_t *fg, const char *pat
        /* Look for ways to cheat...er...avoid the full regex engine. */
        for (i = 0; i < fg->patternLen; i++)
        {
-               /* Can still cheat? */
-               if ((isalnum(fg->pattern[i])) || isspace(fg->pattern[i]) ||
-                   (fg->pattern[i] == '_') || (fg->pattern[i] == ',') ||
-                   (fg->pattern[i] == '=') || (fg->pattern[i] == '-') ||
-                   (fg->pattern[i] == ':') || (fg->pattern[i] == '/')) {
-                       /* As long as it is good, upper case it for later. */
-                       if (iflag)
-                               fg->pattern[i] = toupper(fg->pattern[i]);
-               } else if (fg->pattern[i] == '.') {
+               switch (fg->pattern[i]) {
+               case '.':
                        hasDot = i;
                        if (i < fg->patternLen / 2) {
                                if (firstHalfDot < 0)
@@ -368,11 +361,23 @@ fastcomp(fastgrep_t *fg, const char *pat
                                if (firstLastHalfDot < 0)
                                        firstLastHalfDot = i;
                        }
-               } else {
+                       break;
+               case '\\':
+               case '[':
+               case '(':
+               case '{':
+               case '?':
+               case '*':
+               case '+':
+               case '|':
                        /* Free memory and let others know this is empty. */
                        free(fg->pattern);
                        fg->pattern = NULL;
                        return (-1);
+               default:
+                       if (iflag)
+                               fg->pattern[i] = toupper(fg->pattern[i]);
+                       break;
                }
        }