binary - Convert bit sequence to uint32_t in c++ -

user specifies register (lfsr) length integer parameter function, example enters number 5. need initialize 5-bit length lfsr 1 bits (for length 5 11111) , seed mask in format uint32_t - 5-length register 0x0001f.

what best way mask 0x0001f 5 bit length register when user enters length of register integer number 5?

to generate mask of n bits (where n < 32):

uint32_t mask = (1u << n) - 1u; 

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explanation: consider example n = 5:

1u << n = 1u << 5 = 0000 0000 0000 0000 0000 0000 0010 0000 = 0x20 

then subtract 1 , get:

                    0000 0000 0000 0000 0000 0000 0001 1111 = 0x1f