Re: [unavailable values part 1, 06/17] array element repeats, <unavailable> confused with 0.

[Pedro Alves <pedro@codesourcery.com>]

On Monday 14 February 2011 12:00:16, Jan Kratochvil wrote:
> > --- src.orig/gdb/value.h	2011-02-07 11:15:02.926705996 +0000
> > +++ src/gdb/value.h	2011-02-07 11:15:23.176706001 +0000
> > @@ -374,6 +374,31 @@ extern int value_bytes_available (const
> >  extern void mark_value_bytes_unavailable (struct value *value,
> >  					  int offset, int length);
> >  
> > +/* Compare LENGTH bytes of VAL1's contents starting at OFFSET1 with
> > +   LENGTH bytes of VAL2's contents starting at OFFSET2.  Returns true
> 
> /* OFFSET1 and OFFSET2 should include possible EMBEDDED_OFFSET.  */

Ah, I can see how someone not looking at the implementation might
not realize which "contents" are we talking about.  I've extended
the describing comment.

> > +int
> > +value_available_contents_eq (const struct value *val1, int offset1,
> > +			     const struct value *val2, int offset2,
> > +			     int length)
> > +{
> > +  int org_len = length;
> > +  int org_offset1 = offset1;
> > +  int org_offset2 = offset2;
> 
> All the org_* fields can be dropped by reusing other variables making the code
> more readable.

You're right!  I like that change.

> > +
> > +      /* Compare the _available_ contents.  */
> > +      if (memcmp (val1->contents + org_offset1 + prev_avail,
> > +		  val2->contents + org_offset2 + prev_avail,
> > +		  l2 - prev_avail) != 0)
> 
> `l2 - prev_avail' is not right.  `l2' is already this available chunk size,
> `prev_avail' can be much larger covering all the preceding ranges,
> `prev_avail' is already subtracted from `l2' by `offset1'/`offset2' above.

Indeed.  Could you double-check the patch below?

Thanks!

Pedro Alves

2011-02-15  Pedro Alves  <pedro@codesourcery.com>
	    Jan Kratochvil  <jan.kratochvil@redhat.com>

	gdb/
	* value.c (value_available_contents_eq): Remove redundant local
	variables.  Fix available contents comparision.
	* value.h (value_available_contents_eq): Extend describing
	comment.

---
 gdb/value.c |   19 ++++---------------
 gdb/value.h |   21 +++++++++++++++------
 2 files changed, 19 insertions(+), 21 deletions(-)

Index: src/gdb/value.c
===================================================================
--- src.orig/gdb/value.c	2011-02-15 16:19:15.000000000 +0000
+++ src/gdb/value.c	2011-02-15 17:51:58.018123001 +0000
@@ -533,21 +533,13 @@ value_available_contents_eq (const struc
 			     const struct value *val2, int offset2,
 			     int length)
 {
-  int org_len = length;
-  int org_offset1 = offset1;
-  int org_offset2 = offset2;
   int idx1 = 0, idx2 = 0;
-  int prev_avail;
 
   /* This routine is used by printing routines, where we should
      already have read the value.  Note that we only know whether a
      value chunk is available if we've tried to read it.  */
   gdb_assert (!val1->lazy && !val2->lazy);
 
-  /* The offset from either ORG_OFFSET1 or ORG_OFFSET2 where the
-     available contents we haven't compared yet start.  */
-  prev_avail = 0;
-
   while (length > 0)
     {
       range_s *r1, *r2;
@@ -561,9 +553,9 @@ value_available_contents_eq (const struc
 
       /* The usual case is for both values to be completely available.  */
       if (idx1 == -1 && idx2 == -1)
-	return (memcmp (val1->contents + org_offset1 + prev_avail,
-			val2->contents + org_offset2 + prev_avail,
-			org_len - prev_avail) == 0);
+	return (memcmp (val1->contents + offset1,
+			val2->contents + offset2,
+			length) == 0);
       /* The contents only match equal if the available set matches as
 	 well.  */
       else if (idx1 == -1 || idx2 == -1)
@@ -596,12 +588,9 @@ value_available_contents_eq (const struc
 	return 0;
 
       /* Compare the _available_ contents.  */
-      if (memcmp (val1->contents + org_offset1 + prev_avail,
-		  val2->contents + org_offset2 + prev_avail,
-		  l2 - prev_avail) != 0)
+      if (memcmp (val1->contents + offset1, val2->contents + offset2, l1) != 0)
 	return 0;
 
-      prev_avail += h1;
       length -= h1;
       offset1 += h1;
       offset2 += h1;
Index: src/gdb/value.h
===================================================================
--- src.orig/gdb/value.h	2011-02-14 21:51:17.000000000 +0000
+++ src/gdb/value.h	2011-02-15 18:11:23.938123001 +0000
@@ -379,12 +379,21 @@ extern void mark_value_bytes_unavailable
 					  int offset, int length);
 
 /* Compare LENGTH bytes of VAL1's contents starting at OFFSET1 with
-   LENGTH bytes of VAL2's contents starting at OFFSET2.  Returns true
-   iff the set of available contents match.  Unavailable contents
-   compare equal with unavailable contents, and different with any
-   available byte.  For example, if 'x's represent an unavailable
-   byte, and 'V' and 'Z' represent different available bytes, in a
-   value with length 16:
+   LENGTH bytes of VAL2's contents starting at OFFSET2.
+
+   Note that "contents" refers to the whole value's contents
+   (value_contents_all), without any embedded offset adjustment.  For
+   example, to compare a complete object value with itself, including
+   its enclosing type chunk, you'd do:
+
+     int len = TYPE_LENGTH (check_typedef (value_enclosing_type (val)));
+     value_available_contents (val, 0, val, 0, len);
+
+   Returns true iff the set of available contents match.  Unavailable
+   contents compare equal with unavailable contents, and different
+   with any available byte.  For example, if 'x's represent an
+   unavailable byte, and 'V' and 'Z' represent different available
+   bytes, in a value with length 16:
 
    offset:   0   4   8   12  16
    contents: xxxxVVVVxxxxVVZZ