Re: coreutils 7.1.49-ebb9 FTB risc/HP-UX

[Jim Meyering]

Eric Blake wrote:
> According to Jim Meyering on 3/19/2009 3:58 PM:
>> * src/dd.c (O_FULLBLOCK): Compute its value via cpp macros that
>> expand to less than 3KB of rather than to 180KB(!).
>
> Why use a macro at all?  All we have to do is come up with a value that is
> bitwise distinct from all the others.  In other words, much smaller than
> 3KB, let alone 180KB.
>
> --
> Don't work too hard, make some time for fun as well!
>
> Eric Blake             address@hidden
>>From d6a83c9d49c2737a9a0ef9ca7fc4bb9f469e9576 Mon Sep 17 00:00:00 2001
> From: Eric Blake <address@hidden>
> Date: Thu, 19 Mar 2009 22:31:16 -0600
> Subject: [PATCH] dd: use a more portable definition of O_FULLBLOCK
>
> * src/dd.c (O_FULLBLOCK): Compute its value without using a 180KB
> macro.  This avoids triggering a compilation failure with HP-UX's cc.
> Reported by Matthew Woehlke.

I like it.  Thanks.
However, I'd like to keep O_FULLBLOCK as a single-bit value.
That's slightly less surprising, and makes the change a tad
smaller.  How about this?

>From 8e48bb674042700f7c091f053ae5128e6ca691d7 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Thu, 19 Mar 2009 20:14:26 +0100
Subject: [PATCH] dd: use a more portable definition of O_FULLBLOCK

* src/dd.c (O_FULLBLOCK): Compute its value without using a 180KB
macro.  This avoids triggering a compilation failure with HP-UX's cc.
Reported by Matthew Woehlke.
---
 src/dd.c |   33 ++++++++++++++++++---------------
 1 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/src/dd.c b/src/dd.c
index 9a1c875..a1bbd7f 100644
--- a/src/dd.c
+++ b/src/dd.c
@@ -265,23 +265,26 @@ static struct symbol_value const conversions[] =

 enum
   {
-    /* Use a value that is larger than that of any other O_ symbol.  */
-    O_FULLBLOCK = ((MAX (O_APPEND,
-                   MAX (O_BINARY,
-                   MAX (O_CIO,
-                   MAX (O_DIRECT,
-                   MAX (O_DIRECTORY,
-                   MAX (O_DSYNC,
-                   MAX (O_NOATIME,
-                   MAX (O_NOCTTY,
-                   MAX (O_NOFOLLOW,
-                   MAX (O_NOLINKS,
-                   MAX (O_NONBLOCK,
-                   MAX (O_SYNC,
-                   MAX (O_TEXT, 0)))))))))))))) << 1)
+    /* Compute a value that's bitwise disjoint from the union
+       of all O_ values.  */
+    v = ~(O_APPEND
+          | O_BINARY
+          | O_CIO
+          | O_DIRECT
+          | O_DIRECTORY
+          | O_DSYNC
+          | O_NOATIME
+          | O_NOCTTY
+          | O_NOFOLLOW
+          | O_NOLINKS
+          | O_NONBLOCK
+          | O_SYNC
+          | O_TEXT),
+    /* Use its lowest bit.  */
+    O_FULLBLOCK = v ^ (v & (v - 1))
   };

-/* Ensure that we didn't shift it off the end.  */
+/* Ensure that we got something.  */
 verify (O_FULLBLOCK != 0);

 #define MULTIPLE_BITS_SET(i) (((i) & ((i) - 1)) != 0)
--
1.6.2.rc1.285.gc5f54