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bug#20783: 25.0.50; [PATCH] byte-to-position has internal off-by-one bug
From: |
Wolfgang Jenkner |
Subject: |
bug#20783: 25.0.50; [PATCH] byte-to-position has internal off-by-one bug |
Date: |
Thu, 11 Jun 2015 17:24:42 +0200 |
User-agent: |
Gnus/5.130014 (Ma Gnus v0.14) Emacs/25.0.50 (berkeley-unix) |
On Wed, Jun 10 2015, Eli Zaretskii wrote:
> Wouldn't it be better to handle this use case in Fbyte_to_position?
> The BYTE_TO_CHAR macro is called an awful lot in the Emacs innermost
> loops, and it's _always_ called with a byte position that's on a
> character boundary.
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));
}
DEFUN ("following-char", Ffollowing_char, Sfollowing_char, 0, 0, 0,
--
2.4.2