From: Joe Perches <joe@perches.com>
To: David Miller <davem@davemloft.net>
Cc: shhuiw@gmail.com, fubar@us.ibm.com, andy@greyhouse.net,
netdev@vger.kernel.org
Subject: Re: [PATCH] bonding: use pre-defined macro in bond_mode_name instead of magic number 0
Date: Fri, 26 Jul 2013 14:25:58 -0700 [thread overview]
Message-ID: <1374873958.2009.9.camel@joe-AO722> (raw)
In-Reply-To: <20130726.135330.232525167518786234.davem@davemloft.net>
On Fri, 2013-07-26 at 13:53 -0700, David Miller wrote:
> From: Joe Perches <joe@perches.com>
> Date: Wed, 24 Jul 2013 00:10:19 -0700
>
> > Probably be simpler, less confusing, and more normal style
> > to use a switch case.
> >
> > switch (mode) {
> > case BOND_MODE_ROUNDROBIN:
> > return "load balancing (round-robin)";
> > case BOND_MODE_ACTIVEBACKUP:
> > return "fault-tolerance (active-backup)";
> > case BOND_MODE_XOR:
> > return "load balancing (xor)";
> > case BOND_MODE_BROADCAST;
> > return "fault-tolerance (broadcast)";
> > case BOND_MODE_8023AD:
> > return "IEEE 802.3ad Dynamic link aggregation";
> > case BOND_MODE_TLB:
> > return "transmit load balancing";
> > case BOND_MODE_ALB:
> > return "adaptive load balancing";
> > default:
> > return "unknown";
> > }
>
> I have to say that I do not prefer this approach.
>
> I have a good idea what the compiler ends up outputting for the above,
> and the "indexed table of strings" approach is much less code.
>
just fyi: it doesn't seem like "much less" to at least gcc 4.7
$ cat t1.c
#include <stdio.h>
#include <stdlib.h>
const char * __attribute__((noinline)) string1(int index)
{
static const char *strings[] = {
[0] = "String10",
[1] = "String11",
[2] = "String12",
[3] = "String13",
[4] = "String14",
[5] = "String15",
};
if (index < 0 || index > 5)
return NULL;
return strings[index];
}
const char * __attribute__((noinline)) string2(int index)
{
switch (index) {
case 0: return "String20";
case 1: return "String21";
case 2: return "String22";
case 3: return "String23";
case 4: return "String24";
case 5: return "String25";
}
return NULL;
}
int main(int argc, char** argv)
{
int val;
srand(time(NULL));
val = rand()%6;
printf("1: %s, 2: %s\n", string1(val), string2(val));
return 0;
}
$ gcc -S -O2 t1.c
$ cat t1.s
.file "t1.c"
.text
.p2align 4,,15
.globl string1
.type string1, @function
string1:
.LFB38:
.cfi_startproc
movl 4(%esp), %eax
cmpl $5, %eax
ja .L3
movl strings.2633(,%eax,4), %eax
ret
.p2align 4,,7
.p2align 3
.L3:
xorl %eax, %eax
ret
.cfi_endproc
.LFE38:
.size string1, .-string1
.p2align 4,,15
.globl string2
.type string2, @function
string2:
.LFB39:
.cfi_startproc
movl 4(%esp), %edx
xorl %eax, %eax
cmpl $5, %edx
ja .L6
movl CSWTCH.5(,%edx,4), %eax
.L6:
rep
ret
.cfi_endproc
.LFE39:
.size string2, .-string2
.section .rodata.str1.1,"aMS",@progbits,1
.LC0:
.string "1: %s, 2: %s\n"
.section .text.startup,"ax",@progbits
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB40:
.cfi_startproc
pushl %ebp
.cfi_def_cfa_offset 8
.cfi_offset 5, -8
movl %esp, %ebp
.cfi_def_cfa_register 5
pushl %esi
pushl %ebx
.cfi_offset 6, -12
.cfi_offset 3, -16
movl $715827883, %ebx
andl $-16, %esp
subl $16, %esp
movl $0, (%esp)
call time
movl %eax, (%esp)
call srand
call rand
movl %eax, %ecx
imull %ebx
movl %ecx, %eax
sarl $31, %eax
movl %edx, %ebx
subl %eax, %ebx
leal (%ebx,%ebx,2), %eax
movl %ecx, %ebx
addl %eax, %eax
subl %eax, %ebx
movl %ebx, (%esp)
call string2
movl %ebx, (%esp)
movl %eax, %esi
call string1
movl %esi, 12(%esp)
movl $.LC0, 4(%esp)
movl $1, (%esp)
movl %eax, 8(%esp)
call __printf_chk
leal -8(%ebp), %esp
xorl %eax, %eax
popl %ebx
.cfi_restore 3
popl %esi
.cfi_restore 6
popl %ebp
.cfi_restore 5
.cfi_def_cfa 4, 4
ret
.cfi_endproc
.LFE40:
.size main, .-main
.section .rodata.str1.1
.LC1:
.string "String10"
.LC2:
.string "String11"
.LC3:
.string "String12"
.LC4:
.string "String13"
.LC5:
.string "String14"
.LC6:
.string "String15"
.section .rodata
.align 4
.type strings.2633, @object
.size strings.2633, 24
strings.2633:
.long .LC1
.long .LC2
.long .LC3
.long .LC4
.long .LC5
.long .LC6
.section .rodata.str1.1
.LC7:
.string "String20"
.LC8:
.string "String21"
.LC9:
.string "String22"
.LC10:
.string "String23"
.LC11:
.string "String24"
.LC12:
.string "String25"
.section .rodata
.align 4
.type CSWTCH.5, @object
.size CSWTCH.5, 24
CSWTCH.5:
.long .LC7
.long .LC8
.long .LC9
.long .LC10
.long .LC11
.long .LC12
.ident "GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3"
.section .note.GNU-stack,"",@progbits
next prev parent reply other threads:[~2013-07-26 21:26 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-24 6:53 [PATCH] bonding: use pre-defined macro in bond_mode_name instead of magic number 0 Wang Sheng-Hui
2013-07-24 7:10 ` Joe Perches
2013-07-24 12:38 ` Wang Sheng-Hui
2013-07-26 20:53 ` David Miller
2013-07-26 20:56 ` Joe Perches
2013-07-26 21:25 ` Joe Perches [this message]
2013-07-26 20:54 ` David Miller
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