re_intuit_start(): assert substr offsets are >= 0.

Some parts of this function handle the negative offset case, while other
parts don't. Also, nothing in the test suite generates negative offsets.

So for now, assert that all offsets are positive, and strip out any
code that handles negative offsets. This will make my current activity
in fixing and refactoring this function easier. If at some future point
someone wants to add support for negative offsets (e.g. with look-behind)
then they'll have to add support fully to re_intuit_start() from scratch.

diff --git a/regexec.c b/regexec.c
index 5736625..f651fd5 100644 (file)
--- a/regexec.c
+++ b/regexec.c
@@ -658,6 +658,19 @@ Perl_re_intuit_start(pTHX_
     DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
                 "Intuit: trying to determine minimum start position...\n"));
 
+    /* for now, assume that all substr offsets are positive. If at some point
+     * in the future someone wants to do clever things with look-behind and
+     * -ve offsets, they'll need to fix up any code in this function
+     * which uses these offsets. See the thread beginning
+     * <20140113145929.GF27210@iabyn.com>
+     */
+    assert(prog->substrs->data[0].min_offset >= 0);
+    assert(prog->substrs->data[0].max_offset >= 0);
+    assert(prog->substrs->data[1].min_offset >= 0);
+    assert(prog->substrs->data[1].max_offset >= 0);
+    assert(prog->substrs->data[2].min_offset >= 0);
+    assert(prog->substrs->data[2].max_offset >= 0);
+
     /* CHR_DIST() would be more correct here but it makes things slow. */
     if (prog->minlen > strend - strpos) {
        DEBUG_EXECUTE_r(PerlIO_printf(Perl_debug_log,
@@ -797,11 +810,6 @@ Perl_re_intuit_start(pTHX_
         U8* start_point;
         U8* end_point;
 
-        if (srch_start_shift < 0 && strbeg - s > srch_start_shift) {
-           srch_end_shift -= ((strbeg - s) - srch_start_shift); 
-           srch_start_shift = strbeg - s;
-       }
-
         DEBUG_OPTIMISE_MORE_r({
             PerlIO_printf(Perl_debug_log,
                 "  At restart: s=%"IVdf" Check offset min: %"IVdf
@@ -819,7 +827,7 @@ Perl_re_intuit_start(pTHX_
             start_point= (U8*)(s + srch_start_shift);
             end_point= (U8*)(strend - srch_end_shift);
         } else {
-           start_point= HOP3(s, srch_start_shift, srch_start_shift < 0 ? strbeg : strend);
+           start_point= HOP3(s, srch_start_shift, strend);
             end_point= HOP3(strend, -srch_end_shift, strbeg);
        }
 
@@ -829,7 +837,6 @@ Perl_re_intuit_start(pTHX_
         {
             U8 *p = (U8*)s;
 
-            assert(prog->check_offset_max >= 0);
             if (srch_start_shift > 0)
                 p = start_point; /* don't HOP over chars already HOPed */
             if (p < end_point)
@@ -1071,7 +1078,7 @@ Perl_re_intuit_start(pTHX_
     }
 
     
-    t= (char*)HOP3( s, -prog->check_offset_max, (prog->check_offset_max<0) ? strend : strpos);
+    t= (char*)HOP3( s, -prog->check_offset_max, strpos);
         
     DEBUG_OPTIMISE_MORE_r(
         PerlIO_printf(Perl_debug_log, 
@@ -1088,7 +1095,7 @@ Perl_re_intuit_start(pTHX_
 
     if (s - strpos > prog->check_offset_max  /* signed-corrected t > strpos */
         && (!utf8_target
-           || ((t = (char*)reghopmaybe3((U8*)s, -prog->check_offset_max, (U8*) ((prog->check_offset_max<0) ? strend : strpos)))
+           || ((t = (char*)reghopmaybe3((U8*)s, -prog->check_offset_max, (U8*) strpos))
                 && t > strpos))) 
     {
        /* Fixed substring is found far enough so that the match