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I know the binary representation of -127 is 10000001 (complement).
Can any body tell me why I right shift it by 1 digit, then I get 11000000 ?
(-127) = 10000001
(-127>>1) = 11000000 ???
Thanks.
If your programming language does a sign-extending right shift (as Java does), then the left-most 1 comes from extending the sign. That is, because the top bit was set in the original number it remains set in the result for each shift (so shifting by more than 1 has all 1’s in the top most bits corresponding to the number of shifts done).
This is language dependent – IIRC C and C++ sign-extend on right shift for a signed value and do not for an unsigned value. Java has a special >>> operator to shift without extending (in java all numeric primitive values are signed, including the misleadingly named byte).