Date: Mon, 4 May 2009 12:22:49 +0530 From: Channa <channa.kad@gmail.com> To: Mark Tinguely <tinguely@casselton.net>, Olivier Houchard <mlfbsd@ci0.org> Cc: freebsd-arm@freebsd.org Subject: Re: strncmp issue Message-ID: <515c64960905032352j25edfbcajb3d146fa769b97bb@mail.gmail.com> In-Reply-To: <200904301705.n3UH5wg2057498@casselton.net> References: <20090430.000846.1484329326.imp@bsdimp.com> <200904301705.n3UH5wg2057498@casselton.net>
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Hi,
Thanks for the fix.
I used your code and tested it works fine.
But i have one doubt in the code below you have added
:
- cmpcs r2, #1
+ beq 2f
+ cmp r2, #1
:
Instead of the branch instruction above replace the instruction
'cmpcs' with 'cmp'
since we are comparing unsigned value in 'r2' with a constant.
So the code looks as below
:
- cmpcs r2, #1
+ cmp r2, #1
:
I have tested the above fix it works good for me.
Please let me know your views.
Thanks & Regards,
Channa
2009/4/30 Mark Tinguely <tinguely@casselton.net>:
>
>> =A0Yes. =A0We should get the following results:
>>
>> =A0 =A0 =A0 strncmp("a", "b", 0); =A0 =A0 0
>> =A0 =A0 =A0 strncmp("a", "b", *); =A0 =A0 < 0
>>
>> =A0where * is any other number :)
>>
>> =A0Warner
>
> ENTRY(strncmp)
> /* if (len =3D=3D 0) return 0 */
> =A0 =A0 =A0 =A0cmp =A0 =A0 r2, #0
> =A0 =A0 =A0 =A0moveq =A0 r0, #0
> =A0 =A0 =A0 =A0RETeq
>
> /* ip =3D=3D last src address to compare */
> =A0 =A0 =A0 =A0add =A0 =A0 ip, r0, r2
> 1:
> =A0 =A0 =A0 =A0ldrb =A0 =A0r2, [r0], #1
> =A0 =A0 =A0 =A0ldrb =A0 =A0r3, [r1], #1
> =A0 =A0 =A0 =A0cmp =A0 =A0 ip, r0
> - =A0 =A0 =A0 cmpcs =A0 r2, #1
> + =A0 =A0 =A0 beq =A0 =A0 2f
> + =A0 =A0 =A0 cmp =A0 =A0 r2, #1
> =A0 =A0 =A0 =A0cmpcs =A0 r2, r3
> =A0 =A0 =A0 =A0beq =A0 =A0 1b
> +2:
> =A0 =A0 =A0 =A0sub =A0 =A0 r0, r2, r3
> =A0 =A0 =A0 =A0RET
>
> also ip < r0 if r2 =3D (unsigned int) -1 using 32 bit math. so original
> loop will terminate and compare the first characters. For example
> strncmp("ab", "aa", -1) will result is 0.
>
> I sent Olivier a couple patches, both wrong. Again, sorry for all the noi=
se.
>
> The above code, though, should work in all cases.
>
> =A0 =A0 =A0 =A0strncmp("b", "a", 0) =A0result is 0
> =A0 =A0 =A0 =A0strncmp("abcdef", "abcdef", n) =A0result is 0
> =A0 =A0 =A0 =A0strncmp("abcde", "abcdef", n) =A0 0 if 0 <=3D n < 6 =A0neg=
if n < 0 or n > 5
> =A0 =A0 =A0 =A0strncmp("abcdef", "abcde", n) =A0 0 if 0 <=3D n < 6 =A0pos=
if n < 0 or n > 5
>
>
> The "beq" will break out of the loop if we give a count <=3D the string
> length the first arguement.
>
> The next cmp looks for the NULL byte, and the last cmp checks the charact=
ers
> in the strings.
>
> --Mark.
>
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