Bit puzzeling

[John Erlandsson]

Hi!

I am looking for a good way of assigning a specific bit in a variable the value of a specific bit in another variable.

For example bit 2 in variable a = bit 5 in variable b.

Any suggestions?


//John

[oogabooga]

Maybe not the best way, but:

    unsigned a = 0x00, b = 0xff;
    int abit  = 2, bbit = 5;

    if (b & (1 << bbit))
        a |= (1 << abit);
    else
        a &= -1 ^ (1 << abit);

[nonoob]

-1 ^ is a curious way of saying ~

[oogabooga]

-1 ^ is a curious way of saying ~

Thanks nonoob. I thought that part looked weird. I don't twiddle bits very often, hence "maybe not the best way". This looks much better:

    unsigned a = 0x00, b = 0xff;
    int abit  = 2, bbit = 5;

    if (b & (1 << bbit))
        a |= (1 << abit);
    else
        a &= ~(1 << abit);

[John Erlandsson]

Thanks for helping!