Function: set-buffer-multibyte
set-buffer-multibyte is a function defined in buffer.c.
Signature
(set-buffer-multibyte FLAG)
Documentation
Set the multibyte flag of the current buffer to FLAG.
If FLAG is t, this makes the buffer a multibyte buffer.
If FLAG is nil, this makes the buffer a single-byte buffer.
In these cases, the buffer contents remain unchanged as a sequence of
bytes but the contents viewed as characters do change.
If FLAG is to, this makes the buffer a multibyte buffer by changing
all eight-bit bytes to eight-bit characters.
If the multibyte flag was really changed, undo information of the
current buffer is cleared.
Probably introduced at or before Emacs version 20.3.
Source Code
// Defined in /usr/src/emacs/src/buffer.c
// Skipping highlighting due to helpful-max-highlight.
{
struct Lisp_Marker *tail, *markers;
Lisp_Object btail, other;
ptrdiff_t begv, zv;
bool narrowed = (BEG != BEGV || Z != ZV);
bool modified_p = !NILP (Fbuffer_modified_p (Qnil));
Lisp_Object old_undo = BVAR (current_buffer, undo_list);
if (current_buffer->base_buffer)
error ("Cannot do `set-buffer-multibyte' on an indirect buffer");
/* Do nothing if nothing actually changes. */
if (NILP (flag) == NILP (BVAR (current_buffer, enable_multibyte_characters)))
return flag;
/* Don't record these buffer changes. We will put a special undo entry
instead. */
bset_undo_list (current_buffer, Qt);
/* If the cached position is for this buffer, clear it out. */
clear_charpos_cache (current_buffer);
if (NILP (flag))
begv = BEGV_BYTE, zv = ZV_BYTE;
else
begv = BEGV, zv = ZV;
if (narrowed)
error ("Changing multibyteness in a narrowed buffer");
invalidate_buffer_caches (current_buffer, BEGV, ZV);
if (NILP (flag))
{
ptrdiff_t pos, stop;
unsigned char *p;
/* Do this first, so it can use CHAR_TO_BYTE
to calculate the old correspondences. */
set_intervals_multibyte (false);
set_overlays_multibyte (false);
bset_enable_multibyte_characters (current_buffer, Qnil);
Z = Z_BYTE;
BEGV = BEGV_BYTE;
ZV = ZV_BYTE;
GPT = GPT_BYTE;
TEMP_SET_PT_BOTH (PT_BYTE, PT_BYTE);
for (tail = BUF_MARKERS (current_buffer); tail; tail = tail->next)
tail->charpos = tail->bytepos;
/* Convert multibyte form of 8-bit characters to unibyte. */
pos = BEG;
stop = GPT;
p = BEG_ADDR;
while (1)
{
if (pos == stop)
{
if (pos == Z)
break;
p = GAP_END_ADDR;
stop = Z;
}
if (ASCII_CHAR_P (*p))
p++, pos++;
else if (CHAR_BYTE8_HEAD_P (*p))
{
int bytes, c = string_char_and_length (p, &bytes);
/* Delete all bytes for this 8-bit character but the
last one, and change the last one to the character
code. */
bytes--;
del_range_2 (pos, pos, pos + bytes, pos + bytes, 0);
p = GAP_END_ADDR;
*p++ = c;
pos++;
if (begv > pos)
begv -= bytes;
if (zv > pos)
zv -= bytes;
stop = Z;
}
else
{
int bytes = BYTES_BY_CHAR_HEAD (*p);
p += bytes, pos += bytes;
}
}
}
else
{
ptrdiff_t pt = PT;
ptrdiff_t pos, stop;
unsigned char *p, *pend;
/* Be sure not to have a multibyte sequence striding over the GAP.
Ex: We change this: "...abc\302 _GAP_ \241def..."
to: "...abc _GAP_ \302\241def..." */
if (EQ (flag, Qt)
&& GPT_BYTE > 1 && GPT_BYTE < Z_BYTE
&& ! CHAR_HEAD_P (*(GAP_END_ADDR)))
{
unsigned char *q = GPT_ADDR - 1;
while (! CHAR_HEAD_P (*q) && q > BEG_ADDR) q--;
if (LEADING_CODE_P (*q))
{
ptrdiff_t new_gpt = GPT_BYTE - (GPT_ADDR - q);
move_gap_both (new_gpt, new_gpt);
}
}
/* Make the buffer contents valid as multibyte by converting
8-bit characters to multibyte form. */
pos = BEG;
stop = GPT;
p = BEG_ADDR;
pend = GPT_ADDR;
while (1)
{
int bytes;
if (pos == stop)
{
if (pos == Z)
break;
p = GAP_END_ADDR;
pend = Z_ADDR;
stop = Z;
}
if (ASCII_CHAR_P (*p))
p++, pos++;
else if (EQ (flag, Qt)
&& 0 < (bytes = multibyte_length (p, pend, true, false)))
p += bytes, pos += bytes;
else
{
unsigned char tmp[MAX_MULTIBYTE_LENGTH];
int c;
c = BYTE8_TO_CHAR (*p);
bytes = CHAR_STRING (c, tmp);
*p = tmp[0];
TEMP_SET_PT_BOTH (pos + 1, pos + 1);
bytes--;
insert_1_both ((char *) tmp + 1, bytes, bytes, 1, 0, 0);
/* Now the gap is after the just inserted data. */
pos = GPT;
p = GAP_END_ADDR;
if (pos <= begv)
begv += bytes;
if (pos <= zv)
zv += bytes;
if (pos <= pt)
pt += bytes;
pend = Z_ADDR;
stop = Z;
}
}
if (pt != PT)
TEMP_SET_PT (pt);
/* Do this first, so that chars_in_text asks the right question.
set_intervals_multibyte needs it too. */
bset_enable_multibyte_characters (current_buffer, Qt);
GPT_BYTE = advance_to_char_boundary (GPT_BYTE);
GPT = chars_in_text (BEG_ADDR, GPT_BYTE - BEG_BYTE) + BEG;
Z = chars_in_text (GAP_END_ADDR, Z_BYTE - GPT_BYTE) + GPT;
BEGV_BYTE = advance_to_char_boundary (BEGV_BYTE);
if (BEGV_BYTE > GPT_BYTE)
BEGV = chars_in_text (GAP_END_ADDR, BEGV_BYTE - GPT_BYTE) + GPT;
else
BEGV = chars_in_text (BEG_ADDR, BEGV_BYTE - BEG_BYTE) + BEG;
ZV_BYTE = advance_to_char_boundary (ZV_BYTE);
if (ZV_BYTE > GPT_BYTE)
ZV = chars_in_text (GAP_END_ADDR, ZV_BYTE - GPT_BYTE) + GPT;
else
ZV = chars_in_text (BEG_ADDR, ZV_BYTE - BEG_BYTE) + BEG;
{
ptrdiff_t byte = advance_to_char_boundary (PT_BYTE);
ptrdiff_t position;
if (byte > GPT_BYTE)
position = chars_in_text (GAP_END_ADDR, byte - GPT_BYTE) + GPT;
else
position = chars_in_text (BEG_ADDR, byte - BEG_BYTE) + BEG;
TEMP_SET_PT_BOTH (position, byte);
}
tail = markers = BUF_MARKERS (current_buffer);
/* This prevents BYTE_TO_CHAR (that is, buf_bytepos_to_charpos) from
getting confused by the markers that have not yet been updated.
It is also a signal that it should never create a marker. */
BUF_MARKERS (current_buffer) = NULL;
for (; tail; tail = tail->next)
{
tail->bytepos = advance_to_char_boundary (tail->bytepos);
tail->charpos = BYTE_TO_CHAR (tail->bytepos);
}
/* Make sure no markers were put on the chain
while the chain value was incorrect. */
if (BUF_MARKERS (current_buffer))
emacs_abort ();
BUF_MARKERS (current_buffer) = markers;
/* Do this last, so it can calculate the new correspondences
between chars and bytes. */
/* FIXME: Is it worth the trouble, really? Couldn't we just throw
away all the text-properties instead of trying to guess how
to adjust them? AFAICT the result is not reliable anyway. */
set_intervals_multibyte (true);
set_overlays_multibyte (true);
}
if (!EQ (old_undo, Qt))
{
/* Represent all the above changes by a special undo entry. */
bset_undo_list (current_buffer,
Fcons (list3 (Qapply,
intern ("set-buffer-multibyte"),
NILP (flag) ? Qt : Qnil),
old_undo));
}
current_buffer->prevent_redisplay_optimizations_p = 1;
/* If buffer is shown in a window, let redisplay consider other windows. */
if (buffer_window_count (current_buffer))
windows_or_buffers_changed = 10;
/* Copy this buffer's new multibyte status
into all of its indirect buffers. */
FOR_EACH_LIVE_BUFFER (btail, other)
{
struct buffer *o = XBUFFER (other);
if (o->base_buffer == current_buffer && BUFFER_LIVE_P (o))
{
BVAR (o, enable_multibyte_characters)
= BVAR (current_buffer, enable_multibyte_characters);
o->prevent_redisplay_optimizations_p = true;
}
}
/* Restore the modifiedness of the buffer. */
if (!modified_p && !NILP (Fbuffer_modified_p (Qnil)))
Fset_buffer_modified_p (Qnil);
/* Update coding systems of this buffer's process (if any). */
{
Lisp_Object process;
process = Fget_buffer_process (Fcurrent_buffer ());
if (PROCESSP (process))
setup_process_coding_systems (process);
}
return flag;
}