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From: Jennifer Faggi Renault on 22 Apr 2010 07:03
Hi all,
i want to calcualte A = ROTL(Ac ^ t, u) + S ;
in C code ^ : is the xor function
+ : addition modulo 2^32
ROTL: Circular left bit shift operator of 32-bit nonnegative integer X by n bits

in matlab, i define ROTL function and it works good, and i tried to calculate A
with Ac = '8108B207 '
t = '3BB4E79C'
u= 'BA631FFF'
and S = '8108B207'

after converting each value on uint64 with the cmd: uint64(hex2dec(val)), i did
A= mod(ROTL(bitxor(Ac,t),u) + S, 2^32);
but i get a wrong result A='8108B207' instead of A ='9EE325D5' found with C code

please can any one help me to find the error and fix it, and thanks in advance



From: Yi Cao on 22 Apr 2010 08:01
"Jennifer Faggi Renault" <asma_192(a)live.fr> wrote in message <hqpad9$5q5$1(a)fred.mathworks.com>...
> Hi all,
> i want to calcualte A = ROTL(Ac ^ t, u) + S ;
> in C code ^ : is the xor function
> + : addition modulo 2^32
> ROTL: Circular left bit shift operator of 32-bit nonnegative integer X by n bits
>
> in matlab, i define ROTL function and it works good, and i tried to calculate A
> with Ac = '8108B207 '
> t = '3BB4E79C'
> u= 'BA631FFF'
> and S = '8108B207'
>
> after converting each value on uint64 with the cmd: uint64(hex2dec(val)), i did
> A= mod(ROTL(bitxor(Ac,t),u) + S, 2^32);
> but i get a wrong result A='8108B207' instead of A ='9EE325D5' found with C code
>
> please can any one help me to find the error and fix it, and thanks in advance
>
>
You can diagnose the problem by comparing results at each step. For example, is bitxor(Ac,t) producing the same result as Ac ^ t in C? If so, are ROTL(bitxor(Ac,t),u) in Matlab and ROTL(Ac ^ t, u) in C the same? etc Then, you should be able to find where the problem comes from.

HTH
Yi
From: Jennifer Faggi Renault on 22 Apr 2010 09:26

> You can diagnose the problem by comparing results at each step. For example, is bitxor(Ac,t) producing the same result as Ac ^ t in C? If so, are ROTL(bitxor(Ac,t),u) in Matlab and ROTL(Ac ^ t, u) in C the same? etc Then, you should be able to find where the problem comes from.
>
> HTH
> Yi

Hi, that's exactly what i did, i follow the results of each code step by step and i noticed something weird:
bitxor(Ac,t) gives the same result as (Ac ^ t)
ROTL(bitxor(Ac,t),u) gives wrong result BUT , when i write the numéric values of bitxor(Ac,t) and u i get the true result : i mean
ROTL(1001711516,3127058431) = 1DDA73CE fix the error but
ROTL(v,u) gives 0 (v= bitxor(Ac,t))

why is it different????? can you help me please?
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