Reverse bits in an Integer

A simple function to reverse the bits in an integer

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#include "stdio.h" #include "stdlib.h" /* Function to reverse the bits * Assuming 32 bits. * Simple functionality, get the last bit by right shift * and insert into the output by ORing and then left shifting. * There are better ways to do this. */ void reverse(unsigned *input) { unsigned i=0, mask=0x1, res=0x0, tmp = 0x0; unsigned in = *input; for(i=0; i<32; i++){ tmp = in & mask; in = in >> 1; res = res << 1; res |= tmp; } *input = res; return; } int main(int argc, char **argv) { unsigned input = 0xffffbbbb; printf("%x\n", input); reverse(&input); printf("%x\n", input); return 0; }

[root@Imperfecto_1 ~] gcc run.c && ./a.out
ffffbbbb
ddddffff

[root@Imperfecto_1 ~] echo "ibase=16;obase=2; FFFFBBBB" | bc
11111111111111111011101110111011

[root@Imperfecto_1 ~] echo "ibase=16;obase=2; DDDDFFFF" | bc
11011101110111011111111111111111