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Re: /dev/clipboard pasting with small read() buffer
- From: Corinna Vinschen <corinna-cygwin at cygwin dot com>
- To: cygwin-patches at cygwin dot com
- Date: Thu, 16 Aug 2012 11:33:34 +0200
- Subject: Re: /dev/clipboard pasting with small read() buffer
- References: <502ABB77.2080502@towo.net>
- Reply-to: cygwin-patches at cygwin dot com
Hi Thomas,
thanks for the patch. I have a few minor nits:
On Aug 14 22:56, Thomas Wolff wrote:
> --- sav/fhandler_clipboard.cc 2012-07-08 02:36:47.000000000 +0200
> +++ ./fhandler_clipboard.cc 2012-08-14 18:25:14.903255600 +0200
> @@ -222,6 +222,7 @@ fhandler_dev_clipboard::read (void *ptr,
> UINT formatlist[2];
> int format;
> LPVOID cb_data;
> + int rach;
>
> if (!OpenClipboard (NULL))
> {
> @@ -243,12 +244,18 @@ fhandler_dev_clipboard::read (void *ptr,
> cygcb_t *clipbuf = (cygcb_t *) cb_data;
>
> if (pos < clipbuf->len)
> - {
> + {
> ret = ((len > (clipbuf->len - pos)) ? (clipbuf->len - pos) : len);
> memcpy (ptr, clipbuf->data + pos , ret);
> pos += ret;
> }
> }
> + else if ((rach = get_readahead ()) >= 0)
> + {
> + /* Deliver from read-ahead buffer. */
> + * (char *) ptr = rach;
> + ret = 1;
See (*) below.
> + }
> else
> {
> wchar_t *buf = (wchar_t *) cb_data;
> @@ -256,25 +263,46 @@ fhandler_dev_clipboard::read (void *ptr,
> size_t glen = GlobalSize (hglb) / sizeof (WCHAR) - 1;
> if (pos < glen)
> {
> + /* If caller's buffer is too small to hold at least one
> + max-size character, redirect algorithm to local
> + read-ahead buffer, finally fill class read-ahead buffer
> + with result and feed caller from there. */
> + char * _ptr = (char *) ptr;
> + size_t _len = len;
I would prefer to have local variable names here which don't just
differ by a leading underscore. It's a bit confusing. What about,
say, tmp_ptr/tmp_len, or use_ptr/use_len or something like that?
> + char cprabuf [8 + 1]; /* need this length for surrogates */
> + if (len < 8)
> + {
> + _ptr = cprabuf;
> + _len = 8;
> + }
8? Why 8? The size appears to be rather artificial. The code should
use MB_CUR_MAX instead.
> +
> /* Comparing apples and oranges here, but the below loop could become
> extremly slow otherwise. We rather return a few bytes less than
> possible instead of being even more slow than usual... */
> - if (glen > pos + len)
> - glen = pos + len;
> + if (glen > pos + _len)
> + glen = pos + _len;
> /* This loop is necessary because the number of bytes returned by
> sys_wcstombs does not indicate the number of wide chars used for
> it, so we could potentially drop wide chars. */
> while ((ret = sys_wcstombs (NULL, 0, buf + pos, glen - pos))
> != (size_t) -1
> - && ret > len)
> + && ret > _len)
> --glen;
> if (ret == (size_t) -1)
> ret = 0;
> else
> {
> - ret = sys_wcstombs ((char *) ptr, (size_t) -1,
> + ret = sys_wcstombs ((char *) _ptr, (size_t) -1,
> buf + pos, glen - pos);
> pos = glen;
> + /* If using read-ahead buffer, copy to class read-ahead buffer
> + and deliver first byte. */
> + if (_ptr == cprabuf)
> + {
> + puts_readahead (cprabuf, ret);
> + * (char *) ptr = get_readahead ();
> + ret = 1;
(*) Ok, that works, but wouldn't it be more efficient to do that in
a tiny loop along the lines of
int x;
ret = 0;
while (ret < len && (x = get_readahead ()) >= 0)
ptr++ = x;
ret++;
?
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
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