Bit hack: Expanding bits

Question

I am trying to convert a uint16_t input to a uint32_t bit mask. One bit in the input toggles two bits in the output bit mask. Here is an example conver

Answer 1

Try this, where input16 is the uint16_t input mask:

uint32_t input32 = (uint32_t) input16;
uint32_t result = 0;
uint32_t i;
for(i=0; i<16; i++)
{
    uint32_t bit_at_i = (input32 & (((uint32_t)1) << i)) >> i;
    result |= ((bit_at_i << (i*2)) | (bit_at_i << ((i*2)+1)));
}
// result is now the 32 bit expanded mask