linux-kernel - Re: Improved Swapping Method In sort.c

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Date:	Wed, 30 Apr 2008 19:33:42 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Soumyadip Das Mahapatra <dip_kernel@...oo.co.in>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Improved Swapping Method In sort.c


On Wednesday 2008-04-30 19:09, Soumyadip Das Mahapatra wrote:

>Hello everybody,
>The swapping method (in function void u32_swap() line no.. 14 to 16) in lib/sort.c can be improved by using the following code
>*(u32 *)b ^= *(u32 *)a ^= *(u32 *)b ^= *(u32 *)a instead of the code given. This code
>is not using third variable thus not consuming another memory. And I dont see any significance in
>using *int size* argument. so the function should be
>static void u32_swap(void *a, void *b)
>{
>    *(u32 *)b ^= *(u32 *)a ^= *(u32 *)b ^= *(u32 *)a;
>}

That proposal looks like buggy.

19:32 yaguchi:/dev/shm > cat ui.c 
#include <stdint.h>
#include <stdio.h>

static void u32_swap(void *a, void *b)
{
        *(uint32_t *)b ^= *(uint32_t *)a 
                        ^= *(uint32_t *)b
                        ^= *(uint32_t *)a;
}

int main(void)
{
        uint32_t x = 5, y = 7;
        printf("%u %u\n", x, y);
        u32_swap(&x, &y);
        printf("%u %u\n", x, y);
}
19:32 yaguchi:/dev/shm > ./a.out 
5 7
7 0

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