(s)printf won't do exaxtly what you asked for by itself, since you appear to have reversed the order of the bits in each byte. Assuming that's just an error in entering the question,

$ perl -e 'printf "%016b\n", 1263'
0000010011101111
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converts the integer to a 16-bit binary representation. If you actually do want to reverse the bits in each byte, split or substr and reverse should provide ways to rearrange their order.