Re: modulo question

[Michael Vergoz <descript () secureyourapache com>]

Hello,

--1 will decrement and is not negative.

descript-mac:~ descript$ cat > test.c
int main() {
        printf("%d", --1);
}
descript-mac:~ descript$ cc -o test test.c
test.c: In function `main':
test.c:2: error: invalid lvalue in decrement

and is invalid.

Using modulo with negative numbers ?!
0xFEBA3245-(0xFEBA3245%0x1000) = 4K aligned page.

descript-mac:~ descript$ cat > test.c
int main() {
        long plof = 0xFEBA3245;
        printf("Number : %lx(%ld)\n", plof, plof);
        printf("4Ko alignement: %lx\n", plof-(plof%0x1000));
}
descript-mac:~ descript$ cc -o test test.c
descript-mac:~ descript$ ./test
Number : feba3245(-21351867)
4Ko alignement: feba4000

sya

On 15 avr. 05, at 12:47, martin wrote:

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> Hello list,
>
> I have slightly academic question about modulo. I sent this message 
> here
> because I thing there are many of gurus which working with modulo 
> operator.
>
> I have tried in python and in C++ following:
>             python    C++
> 1%2      1           1
> - -1%2     1          -1
> 1%-2    -1           1
> - -1%-2   -1          -1
>
> What is right?
> Do you know some applications which using modulo with negative numbers?
> Have you some references to definition (mathematical def. and 
> properties) of
> modulo?
>
> Thanks in advance,
> Martin
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