On 5/17/19 4:47 AM, Marco Borsari via fpc-devel wrote:
In the code below
program test;
const n=12;
s=1 shl n;
var a,b,c,h1,h2:word;
ummm... what is 's'? you've used it before it has been defined...
begin
a:=77;
b:=0;
(*c:=(a XOR b)*(a SHL 5+b SHR 2);*)
h1:=((a XOR b)*(a SHL 5+b SHR 2)) SHR (16-n);
(*h1:=c SHR (16-n);*)
h2:=((a XOR b)*(a SHL 5+b SHR 2)) AND ((s-1) SHL (16-n)) SHR (16-n);
(*h2:=c AND ((s-1) SHL (16-n)) SHR (16-n);*)
writeln(h1,',',h2);
end.
the results of h1 and h2 (they are hashes) are different, and only h2
appears to be correct and inside the range.
If we precompute the hash value with c, then both h1 and h2 are
the same.
Does this is an effect of some multiplication overflow,
or is it a bug?
Regards, Marco Borsari
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