[Emacs-diffs] master 2bc90e0c: * src/coding.c (decode_coding): Improve doc.

[Stefan Monnier]

branch: master
commit 2bc90e0ce0f349b8c80aa8df782f991b64aa7398
Author: Stefan Monnier <address@hidden>
Commit: Stefan Monnier <address@hidden>

    * src/coding.c (decode_coding): Improve doc.
---
 src/coding.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/coding.c b/src/coding.c
index 59589ca..e90d571 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -7324,9 +7324,13 @@ produce_annotation (struct coding_system *coding, 
ptrdiff_t pos)
    In this case, if CODING->src_pos is positive, it is a position of
    the source text in the buffer, otherwise, the source text is in the
    gap area of the buffer, and CODING->src_pos specifies the offset of
-   the text from GPT (which must be the same as PT).  If this is the
-   same buffer as CODING->dst_object, CODING->src_pos must be
-   negative.
+   the text from the end of the gap (and GPT must be equal to PT).
+
+   When the text is taken from the gap, it can't be at the beginning
+   of the gap because the new decoded text is progressively acumulated
+   at the beginning of the gap before it gets inserted at PT (this way,
+   as the output grows, the input shrinks, so we only need to allocate
+   enough space for `max(IN, OUT)` instead of `IN + OUT`).
 
    If CODING->src_object is a string, CODING->src_pos is an index to
    that string.