Commit Graph

3 Commits

Author SHA1 Message Date
Trent Piepho
8e2c20023f Fix constant folding and poor optimization in byte swapping code
Constant folding does not work for the swabXX() byte swapping functions,
and the C versions optimize poorly.

Attempting to initialize a global variable to swab16(0x1234) or put
something like "case swab32(42):" in a switch statement will not compile.
It can work, swab.h just isn't doing it correctly.  This patch fixes that.

Contrary to the comment in asm-i386/byteorder.h, gcc does not recognize the
"C" version of swab16 and turn it into efficient code.  gcc can do this,
just not with the current code.  The simple function:

u16 foo(u16 x) { return swab16(x); }

Would compile to:
        movzwl  %ax, %eax
        movl    %eax, %edx
        shrl    $8, %eax
        sall    $8, %edx
        orl     %eax, %edx

With this patch, it will compile to:
        rolw    $8, %ax

I also attempted to document the maze different macros/inline functions
that are used to create the final product.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Cc: Francois-Rene Rideau <fare@tunes.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-05-08 11:14:59 -07:00
Andrew Morton
a136564702 [PATCH] remove gcc-2 checks
Remove various things which were checking for gcc-1.x and gcc-2.x compilers.

From: Adrian Bunk <bunk@stusta.de>

    Some documentation updates and removes some code paths for gcc < 3.2.

Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-01-08 20:14:02 -08:00
Linus Torvalds
1da177e4c3 Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00