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Re: [PATCH]: New sparse bitmap implementation


On 3/20/07, Eric Botcazou <ebotcazou@libertysurf.fr> wrote:
>       * ebitmap.h: New file
>       * ebitmap.c: New file

Minor nits:

--- gcc/ebitmap.c       (revision 0)
+++ gcc/ebitmap.c       (revision 0)
@@ -0,0 +1,1019 @@
+/* Sparse array-based bitmaps.
+   Copyright (C) 2006 Free Software Foundation, Inc.
+   Contributed by Daniel Berlin <dberlin@dberlin.org>

--- gcc/ebitmap.h       (revision 0)
+++ gcc/ebitmap.h       (revision 0)
@@ -0,0 +1,162 @@
+/* Sparse array based bitmaps.
+   Copyright (C) 2007 Free Software Foundation, Inc.

The same copyright date would probably be expected.

Whoops




+ in words that are all zero, the time to test is O(1). For bits + in words that exist, it requires it will require O(n/sizeof(word))

Pasto.

Fixed.

+ easily vectorized. They are all O(number of words) + O(number of + bits that may end up in the destination), as the approriate

Typo in last word.

Fixed

/* #define EBITMAP_DEBUGGING */

Why not predicate the debugging code on --enable-checking=misc?

It's *incredibly* expensive. In most cases, it duplicate the entire operation non-sparsely, bit by bit. In the into versions, it also copies the entire destination bitmap so it can do the operation non-sparsely to verify results. It's also code that only ever needs to be run if you are changing the implementation. Our bitmap/sbitmap code has had such a low rate of change (we usually have one change every few *years*) that it seems "not worth it" even for =misc.



I wish every new file had so thorough a head comment!

Thanks. That was Steven Bosscher's idea, who reminded me that nobody else had any idea how the data structure actually looked and operated :)


-- Eric Botcazou



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