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Date: Mon, 2 Mar 2009 12:50:59 -0300
From: Thiago Galesi <thiagogalesi@...il.com>
To: Pekka Enberg <penberg@...helsinki.fi>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crc32: remove useless __pure modifier from functions
Actually, the effects of most keywords (like const, etc) affect things
outside of the module (the callers)
http://gcc.gnu.org/onlinedocs/gcc-4.2.0/gcc/Function-Attributes.html
has a good explanation.
Briefly, a _pure function only depends on its parameters and the only
return is via the function return, so the compiler can optimize some
of its calls away.
--
-
Thiago Galesi
On Mon, Mar 2, 2009 at 12:18 PM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> From: Pekka Enberg <penberg@...helsinki.fi>
>
> The pure attribute has absolutely no effect with GCC 4.2:
>
> text data bss dec hex filename
> 2456 0 0 2456 998 lib/crc32.o.old
> 2456 0 0 2456 998 lib/crc32.o.new
>
> Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
> ---
> lib/crc32.c | 12 ++++++------
> 1 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/lib/crc32.c b/lib/crc32.c
> index 49d1c9e..9ff76ad 100644
> --- a/lib/crc32.c
> +++ b/lib/crc32.c
> @@ -49,7 +49,7 @@ MODULE_LICENSE("GPL");
> * @p: pointer to buffer over which CRC is run
> * @len: length of buffer @p
> */
> -u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
> +u32 crc32_le(u32 crc, unsigned char const *p, size_t len);
>
> #if CRC_LE_BITS == 1
> /*
> @@ -57,7 +57,7 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len);
> * simplified by inlining the table in ?: form.
> */
>
> -u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
> +u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
> {
> int i;
> while (len--) {
> @@ -69,7 +69,7 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
> }
> #else /* Table-based approach */
>
> -u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
> +u32 crc32_le(u32 crc, unsigned char const *p, size_t len)
> {
> # if CRC_LE_BITS == 8
> const u32 *b =(u32 *)p;
> @@ -145,7 +145,7 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
> * @p: pointer to buffer over which CRC is run
> * @len: length of buffer @p
> */
> -u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
> +u32 crc32_be(u32 crc, unsigned char const *p, size_t len);
>
> #if CRC_BE_BITS == 1
> /*
> @@ -153,7 +153,7 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len);
> * simplified by inlining the table in ?: form.
> */
>
> -u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
> +u32 crc32_be(u32 crc, unsigned char const *p, size_t len)
> {
> int i;
> while (len--) {
> @@ -167,7 +167,7 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
> }
>
> #else /* Table-based approach */
> -u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
> +u32 crc32_be(u32 crc, unsigned char const *p, size_t len)
> {
> # if CRC_BE_BITS == 8
> const u32 *b =(u32 *)p;
> --
> 1.5.4.3
>
>
>
> --
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