Re: [patch #6758] Add support for Atari FreeMiNT OS to fpurge

[Alan Hourihane]

On Sun, 2009-03-01 at 02:17 +0100, Bruno Haible wrote:
> Alan Hourihane wrote:
> +  fp->__pushback_bufp = 0;
> +  if (fp->__mode.__write)
> +    fp->__put_limit = fp->__buffer;
> +  fp->__bufp = fp->__get_limit;
> 
> I don't think the last statement is right. The purpose of fpurge, on the read
> side, is to empty the buffer, i.e. drop all read contents. I do agree that
> at the end of this function, fp->__bufp == fp->__get_limit, should hold.
> 
> Compare what is done on glibc systems. There, essentially
>   #define getc(fp) (fp->_IO_read_ptr < fp->_IO_read_end ? 
> *_fp->_IO_read_ptr++ : ...)
> and fpurge does
>   fp->_IO_read_end = fp->_IO_read_ptr;
> Consequently, on FreeMiNT, where getc is essentially
>   #define getc(fp) (fp->__bufp < fp->__get_limit ? *fp->__bufp++ : ...)
> hence fpurge has to do
>   fp->__get_limit = fp->__bufp;

Quite right. Good catch.

> I propose this instead in fpurge.c
> 
> # elif defined __MINT__             /* Atari FreeMiNT */
>   if (fp->__pushed_back)
>     {
>       fp->__bufp = fp->__pushback_bufp;
>       fp->__pushed_back = 0;
>     }
>   /* Preserve the current file position.  */
>   if (fp->__target != -1)
>     fp->__target += fp->__bufp - fp->__buffer;
>   fp->__bufp = fp->__buffer;
>   /* Nothing in the buffer, next getc is nontrivial.  */
>   fp->__get_limit = fp->__bufp;
>   /* Nothing in the buffer, next putc is nontrivial.  */
>   fp->__put_limit = fp->__buffer;
>   return 0;
> 
> (The 'if (fp->__mode.__write)' in your variant is certainly redundant, right?)

Yes. This works too.

Alan.