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

[ketmar via Digitalmars-d]

On Fri, 21 Nov 2014 14:36:53 -0300
Ary Borenszweig via Digitalmars-d <digitalmars-d at puremagic.com> wrote:

> On 11/21/14, 11:29 AM, ketmar via Digitalmars-d wrote:
> > On Fri, 21 Nov 2014 19:31:23 +1100
> > Daniel Murphy via Digitalmars-d <digitalmars-d at puremagic.com> wrote:
> >
> >> "bearophile"  wrote in message news:lkcltlokangpzzdzzfjg at forum.dlang.org...
> >>
> >>>  From my experience in coding in D they are far more unlikely than
> >>> sign-related bugs of array lengths.
> >>
> >> Here's a simple program to calculate the relative size of two files, that
> >> will not work correctly with unsigned lengths.
> >>
> >> module sizediff
> >>
> >> import std.file;
> >> import std.stdio;
> >>
> >> void main(string[] args)
> >> {
> >>      assert(args.length == 3, "Usage: sizediff file1 file2");
> >>      auto l1 = args[1].read().length;
> >>      auto l2 = args[2].read().length;
> >>      writeln("Difference: ", l1 - l2);
> >> }
> >>
> >> The two ways this can fail (that I want to highlight) are:
> >> 1. If either file is too large to fit in a size_t the result will (probably)
> >> be wrong
> >> 2. If file2 is bigger than file1 the result will be wrong
> >>
> >> If length was signed, problem 2 would not exist, and problem 1 would be more
> >> likely to occur.  I think it's clear that signed lengths would work for more
> >> possible realistic inputs.
> > no, the problem 2 just becomes hidden. while the given code works most
> > of the time, it is still broken.
> 
> So how would you solve problem 2?
with proper check before doing subtraction. or by switching to some
Scheme compiler with full numeric tower.
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