Converting signed binary string in two's complement to int?

Question

I have a binary string as follows:

String bin = "1101";

and I want my int's value to be -3 instead of 13

What is the best way to achieve this?

Are you assuming that every string with a leading 1 is negative? Would 13 have to be represented as "01101"? Or have you got a fixed size of 4 bits? More details required, basically. — Jon Skeet
– Jon Skeet, Commented May 9, 2012 at 8:50
Long res = Long.parseLong(bin, 2); if (bin.charAt(0)=='1' && bin.length()==n) res -= (1L<<n); — bestsss
– bestsss, Commented May 9, 2012 at 9:49

David Schwartz · Accepted Answer · 2012-05-09 08:54:57Z

6

Use if (i >= k) i -= 2 * k; Where k is the smallest positive number your scheme cannot represent. (8 in this case, because 0111 is 7 and 1000 would be negative.)

13 is greater than 8, so you'd subtract 16 from 13, giving -3.

answered May 9, 2012 at 8:54

David Schwartz

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