Swap bits in a number in C [duplicate]

Answer 1

Solution for generic n bits swapping between last and first. Not verified for case when total bits are less than 2n. here 7 is for char, take 31 for integer.

unsigned char swapNbitsFtoL(unsigned char num, char nbits)
{
    unsigned char u1 = 0;
    unsigned char u2 = 0;

    u1 = ~u1;
    u1 &= num;
    u1 = (u1 >> (7 - (nbits - 1))); /* Here nbits is number of n=bits so I have taken (nbits - 1). */

    u2 = ~u2;
    u2 &= num;
    u2 = (u2 << (7 - (nbits - 1))); /* Here nbits is number of n=bits so I have taken (nbits - 1). */

    u1 |= u2; /* u1 have first and last swapped n bits with */

    u2 = 0;
    u2 = ~u2;
    u2 = ((u2 >> (7 - (nbits - 1))) | (u2 << (7 - (nbits - 1))));
    bit_print(u2);
    u2 = ~u2;
    u2 &= num;

    return (u1 | u2);
}