Write a C program to encode bits in a 32-bit number such that, most significant 16 bits should be reversed but lower 16 bits should be untouched. Then asked to generalize this to any number of bits.

Question

Write a C program to encode bits in a 32-bit number such that, most significant 16 bits should be reversed but lower 16 bits should be untouched.  Then asked to generalize this to any number of bits.

Sigiloso · Accepted Answer

The idea is to reverse the entire 32-bits first and then left shift the resulting number by 16 bits so that the upper 16 bits are now reversed. In the second phase, with the help of a mask zero out the most significant 16 bits. Now XOR the two number to get the desired encoded number.

Sigiloso · Answer

To solve this problem, below properties of XOR can be used: 1 ^ x => ~x 0 ^ x => x Step 1: Create a mask with upper 16 bits are set and lower 16 bits are cleared. Step 2: XOR input and mask. Int invertUpper16 (int x) { int mask = ~((1 0000_0000_0000_0001_0000_0000_0000_0000 When we subtract 1 from 1 0000_0000_0000_0000_1111_1111_1111_1111 When we negate (1 1111_1111_1111_1111_0000_0000_0000_0000; Generalized solution: Int invertUpper16 (int x) ; int size = 16; Int mask = ~((1 << (size+1))-1); x ^= mask; Return x; }

Sigiloso · Answer

For some reason, above explanation is got trimmed in the middle (@ int mask = onwards). But anyway, generalized final solution is displayed correct.

Qualcomm

Pergunta de entrevista da empresa Qualcomm

Respostas da entrevista

Empresas seguidas

Buscas de vagas