Re: truncate.c fails to compile on make distcheck

[Paul Eggert]

Pádraig Brady <address@hidden> writes:

> diff --git a/src/truncate.c b/src/truncate.c
> index 02d4102..fd321c6 100644
> --- a/src/truncate.c
> +++ b/src/truncate.c
> @@ -189,9 +189,9 @@ do_ftruncate (int fd, char const *fname, off_t ssize, 
> rel_mode_t rel_mode)
>          }
>  
>        if (rel_mode == rm_min)
> -        nsize = MAX (fsize, ssize);
> +        nsize = MAX (fsize, (uintmax_t) ssize);
>        else if (rel_mode == rm_max)
> -        nsize = MIN (fsize, ssize);
> +        nsize = MIN (fsize, (uintmax_t) ssize);
>        else if (rel_mode == rm_rdn)
>          /* 0..ssize-1 -> 0 */
>          nsize = (fsize / ssize) * ssize;

This patch does not look right to me.  If ssize is negative, it screws up.

Can ssize be negative?  Yes it can.

This indicates a bug in the underlying code, which GCC was right to
warn us about, and which we should not have worked around by inserting
casts blindly.  The code should be inspected carefully to make sure
that it does the right thing when asked to truncate a file to a
negative offset.