Inconsistent signed/unsigned results in right shift

General
1

Hi all,

It seems that (-1)>>(1<<32) and (-1)>>(1<<64) produces inconsistent results (at least with SWI 8.0.3). This is probably due to the transition between small and large integer representations (we are fixing the same bug in Ciao right now). See log attached.

Cheers,
Jose

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?- X is 1 >> (1<<32).
X = 0.

?- X is 1 >> (1<<64).
X = 0.

?- X is 1 >> (1<<128).
X = 0.

?- X is (-1) >> (1<<128).
X = 0.

?- X is (-1) >> (1<<64).
X = 0.

?- X is (-1) >> (1<<32).
X = -1.

?- X is (-1) >> (1<<16).
X = -1.

?-
1 Like
3

By my system are you referring to the machine you are using or Jekejeke Prolog

4

See edited post.

5

I noticed that the examples were run with
SWI-Prolog (threaded, 64 bits, version 8.0.3) so I decided to try the latest version
SWI-Prolog (threaded, 64 bits, version 8.1.19-43-ge65571d98)

The results are the same except for

?- X is (-1) >> (1<<32).
X = 0.
Test cases. Click triangle to expand. 
:- begin_tests(bit_shift).

test(100) :-
    X is 1 >> (1<<16),
    assertion( X == 0 ).

test(200) :-
    X is 1 >> (1<<32),
    assertion( X == 0 ).

test(300) :-
    X is 1 >> (1<<64),
    assertion( X == 0 ).

test(400) :-
    X is 1 >> (1<<128),
    assertion( X == 0 ).

test(600) :-
    X is (-1) >> (1<<16),
    assertion( X == -1 ).

test(700) :-
    X is (-1) >> (1<<32),
    assertion( X == 0 ).

test(800) :-
    X is (-1) >> (1<<64),
    assertion( X == 0 ).

test(900) :-
    X is (-1) >> (1<<128),
    assertion( X == 0 ).

:- end_tests(bit_shift).