Merge branch 'jc/maint-1.6.4-grep-lookahead' into jc/maint-grep-lookahead

* jc/maint-1.6.4-grep-lookahead:
  grep: optimize built-in grep by skipping lines that do not hit

This needs to be an evil merge as fixmatch() changed signature since
5183bf6 (grep: Allow case insensitive search of fixed-strings,
2009-11-06).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --cc grep.c
index bdadf2c0ccfafc18011beee3bc05754860392523,03ffcd4042e95b521e2aed03ecf2ae6d65fef41c..62723da1340d8b1e7ddbe00544dadbfc5abf4c8c
--- 1/grep.c
--- 2/grep.c
+++ b/grep.c
@@@ -615,6 -608,65 +615,65 @@@ static void show_pre_context(struct gre
        }
  }
  
 -                      hit = !fixmatch(p->pattern, bol, &m);
+ static int should_lookahead(struct grep_opt *opt)
+ {
+       struct grep_pat *p;
+ 
+       if (opt->extended)
+               return 0; /* punt for too complex stuff */
+       if (opt->invert)
+               return 0;
+       for (p = opt->pattern_list; p; p = p->next) {
+               if (p->token != GREP_PATTERN)
+                       return 0; /* punt for "header only" and stuff */
+       }
+       return 1;
+ }
+ 
+ static int look_ahead(struct grep_opt *opt,
+                     unsigned long *left_p,
+                     unsigned *lno_p,
+                     char **bol_p)
+ {
+       unsigned lno = *lno_p;
+       char *bol = *bol_p;
+       struct grep_pat *p;
+       char *sp, *last_bol;
+       regoff_t earliest = -1;
+ 
+       for (p = opt->pattern_list; p; p = p->next) {
+               int hit;
+               regmatch_t m;
+ 
+               if (p->fixed)
++                      hit = !fixmatch(p->pattern, bol, p->ignore_case, &m);
+               else
+                       hit = !regexec(&p->regexp, bol, 1, &m, 0);
+               if (!hit || m.rm_so < 0 || m.rm_eo < 0)
+                       continue;
+               if (earliest < 0 || m.rm_so < earliest)
+                       earliest = m.rm_so;
+       }
+ 
+       if (earliest < 0) {
+               *bol_p = bol + *left_p;
+               *left_p = 0;
+               return 1;
+       }
+       for (sp = bol + earliest; bol < sp && sp[-1] != '\n'; sp--)
+               ; /* find the beginning of the line */
+       last_bol = sp;
+ 
+       for (sp = bol; sp < last_bol; sp++) {
+               if (*sp == '\n')
+                       lno++;
+       }
+       *left_p -= last_bol - bol;
+       *bol_p = last_bol;
+       *lno_p = lno;
+       return 0;
+ }
+ 
  static int grep_buffer_1(struct grep_opt *opt, const char *name,
                         char *buf, unsigned long size, int collect_hits)
  {