Subject: Re: bug#6524: du now uses less than half as much memory, sometimes

From: Jim Meyering <[email-masked]>
Date: Wed, 07 Jul 2010 14:49:49 +0200

Jim Meyering wrote:
...
> I prefer to use unsigned types when appropriate,
> and adjusted a couple of other things for readability.
> I'll push something like the following later today.
...
> Subject: [PATCH] di-set, ino-map: adjust a type, improve readability
...
>    size_t h = dev;
> -  int i;
> -  for (i = 1; i < sizeof dev / sizeof h + (sizeof dev % sizeof h != 0); i++)
> +  unsigned int i;
> +  unsigned int n_words = sizeof ino / sizeof h + (sizeof ino % sizeof h != 0);

It'd be good if I were to compile before posting a patch ;-)
Those uses of "ino" should be "dev", of course.

>From 8217117f3cb4ee39f8913fcfdef8b3d64dfd2437 Mon Sep 17 00:00:00 2001
From: Jim Meyering <[email-masked]>
Date: Wed, 7 Jul 2010 11:57:26 +0200
Subject: [PATCH] di-set, ino-map: adjust a type, improve readability

* gl/lib/ino-map.c (ino_hash): Declare "i" as unsigned int.
Use an intermediate variable for the for-loop upper bound,
so it's a little more readable.  Adjust comment.
* gl/lib/di-set.c (di_ent_hash): Likewise.
---
 gl/lib/di-set.c  |   10 ++++++----
 gl/lib/ino-map.c |   10 ++++++----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/gl/lib/di-set.c b/gl/lib/di-set.c
index ba44bcf..892950d 100644
--- a/gl/lib/di-set.c
+++ b/gl/lib/di-set.c
@@ -78,11 +78,13 @@ di_ent_hash (void const *x, size_t table_size)
   struct di_ent const *p = x;
   dev_t dev = p->dev;

-  /* Exclusive-OR the words of DEV into H.  This avoids loss of info,
-     without using a wider % that could be quite slow.  */
+  /* When DEV is wider than size_t, exclusive-OR the words of DEV into H.
+     This avoids loss of info, without applying % to the wider type,
+     which could be quite slow on some systems.  */
   size_t h = dev;
-  int i;
-  for (i = 1; i < sizeof dev / sizeof h + (sizeof dev % sizeof h != 0); i++)
+  unsigned int i;
+  unsigned int n_words = sizeof dev / sizeof h + (sizeof dev % sizeof h != 0);
+  for (i = 1; i < n_words; i++)
     h ^= dev >> CHAR_BIT * sizeof h * i;

   return h % table_size;
diff --git a/gl/lib/ino-map.c b/gl/lib/ino-map.c
index cc9a131..f6fdd63 100644
--- a/gl/lib/ino-map.c
+++ b/gl/lib/ino-map.c
@@ -56,11 +56,13 @@ ino_hash (void const *x, size_t table_size)
   struct ino_map_ent const *p = x;
   ino_t ino = p->ino;

-  /* Exclusive-OR the words of INO into H.  This avoids loss of info,
-     without using a wider % that could be quite slow.  */
+  /* When INO is wider than size_t, exclusive-OR the words of INO into H.
+     This avoids loss of info, without applying % to the wider type,
+     which could be quite slow on some systems.  */
   size_t h = ino;
-  int i;
-  for (i = 1; i < sizeof ino / sizeof h + (sizeof ino % sizeof h != 0); i++)
+  unsigned int i;
+  unsigned int n_words = sizeof ino / sizeof h + (sizeof ino % sizeof h != 0);
+  for (i = 1; i < n_words; i++)
     h ^= ino >> CHAR_BIT * sizeof h * i;

   return h % table_size;
--
1.7.2.rc1.218.gca56a