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bug#20783: 25.0.50; [PATCH] byte-to-position has internal off-by-one bug
From: |
Eli Zaretskii |
Subject: |
bug#20783: 25.0.50; [PATCH] byte-to-position has internal off-by-one bug |
Date: |
Thu, 11 Jun 2015 19:04:24 +0300 |
> From: Wolfgang Jenkner <wjenkner@inode.at>
> Cc: 20783@debbugs.gnu.org
> Date: Thu, 11 Jun 2015 17:24:42 +0200
>
> I see. How about something like the patch below? The loop could be
> improved a bit by doing pointer arithmetic like in DEC_POS but it's
> perhaps not worth complicating things for the case where bytepos is not
> at a character boundary.
>
> -- >8 --
> Subject: [PATCH] * editfns.c (Fbyte_to_position): Fix bytepos not at char
> boundary.
>
> The behavior now matches the description in the manual. (Bug#20783)
> ---
> src/editfns.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/src/editfns.c b/src/editfns.c
> index cddb0d4..94715fe 100644
> --- a/src/editfns.c
> +++ b/src/editfns.c
> @@ -1025,10 +1025,18 @@ DEFUN ("byte-to-position", Fbyte_to_position,
> Sbyte_to_position, 1, 1, 0,
> If BYTEPOS is out of range, the value is nil. */)
> (Lisp_Object bytepos)
> {
> + ptrdiff_t pos_byte;
> +
> CHECK_NUMBER (bytepos);
> - if (XINT (bytepos) < BEG_BYTE || XINT (bytepos) > Z_BYTE)
> + pos_byte = XINT (bytepos);
> + if (pos_byte < BEG_BYTE || pos_byte > Z_BYTE)
> return Qnil;
> - return make_number (BYTE_TO_CHAR (XINT (bytepos)));
> + if (Z != Z_BYTE)
> + /* There are multibyte characters in the buffer.
> + Search for the start of the current character. */
> + while (!CHAR_HEAD_P (FETCH_BYTE (pos_byte)))
> + pos_byte--;
> + return make_number (BYTE_TO_CHAR (pos_byte));
> }
Works for me, thanks. But please add a comment there about
BYTE_TO_CHAR expecting byte positions that are on a character
boundary, so that the reason for the loop is clear.