'int' is enough for 'length' to migrate code from x86 to x64

[FrankLike via Digitalmars-d]

> What about:
>
>     uint x;
>     auto z = x - 1;
>
> ?

When mixing signed and unsigned, as signed, it maybe no mistaken.

thhere is a small test,add 'cast(long)' before - operator,if it's 
auto add,maybe fine.
-----

import std.stdio;

void main()
{
	size_t width = 10;
	size_t height = 20;
	writeln("before width is ",width," ,height is ",height);
     height -= 15;
     width -=  cast(long)height;
     writeln("after width is ",width," ,height is ",height);
}
----result: after width is 5 .
it's ok.

Frank