Algorithm for copying N bits at arbitrary position from one int to another

Question

An interesting problem I\'ve been pondering the past few days is how to copy one integer\'s bits into another integer at a given position in the destination integer. So, for exa

Answer 1

It pretty good: I tried this alternate version, but yours was about 30% faster in testing:

    int[] bits = new int[] {0,1,3,7,15,31,63,127,255,511,1023
        ,2047,4095,8192,16383,32767,65535,131071,262143,524287
        ,1048575,2097151,4194303,8388607,16777215,33554431,67108863
        ,134217727,268435455,536870911,1073741823,2147483647,-1};

    public int setbits2(int destination, int source, int at, int numbits)
    {
        int ones = bits[numbits + at] & ~bits[at];
        return (destination & ~ones) | ((source << at) & ones);
    }