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Avoid expensive recoding for ASCII identity cases (bug#40407)

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Optimise for the common case of encoding or decoding an ASCII-only
string using an ASCII-compatible coding, for file names in particular.

* src/coding.c (string_ascii_p): New function.
(code_convert_string): Return the input string for ASCII-only inputs
and ASCII-compatible codings.
* test/src/coding-tests.el (coding-nocopy-ascii): New test.
This commit is contained in:
Mattias Engdegård
2020-04-03 16:01:01 +02:00
parent c7ac76603f
commit 4ed39549e3
2 changed files with 37 additions and 1 deletions
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27
src/coding.c
View File

@@ -9471,6 +9471,17 @@ not fully specified.) */)
return code_convert_region (start, end, coding_system, destination, 1, 0);
}
/* Whether a string only contains chars in the 0..127 range. */
static bool
string_ascii_p (Lisp_Object str)
{
ptrdiff_t nbytes = SBYTES (str);
for (ptrdiff_t i = 0; i < nbytes; i++)
if (SREF (str, i) > 127)
return false;
return true;
}
Lisp_Object
code_convert_string (Lisp_Object string, Lisp_Object coding_system,
Lisp_Object dst_object, bool encodep, bool nocopy,
@@ -9502,7 +9513,21 @@ code_convert_string (Lisp_Object string, Lisp_Object coding_system,
chars = SCHARS (string);
bytes = SBYTES (string);
if (BUFFERP (dst_object))
if (EQ (dst_object, Qt))
{
/* Fast path for ASCII-only input and an ASCII-compatible coding:
act as identity. */
Lisp_Object attrs = CODING_ID_ATTRS (coding.id);
if (! NILP (CODING_ATTR_ASCII_COMPAT (attrs))
&& (STRING_MULTIBYTE (string)
? (chars == bytes) : string_ascii_p (string)))
return (nocopy
? string
: (encodep
? make_unibyte_string (SDATA (string), bytes)
: make_multibyte_string (SDATA (string), bytes, bytes)));
}
else if (BUFFERP (dst_object))
{
struct buffer *buf = XBUFFER (dst_object);
ptrdiff_t buf_pt = BUF_PT (buf);

11
test/src/coding-tests.el
View File

@@ -383,6 +383,17 @@
(should-not (eq (encode-coding-string s nil nil) s))
(should (eq (encode-coding-string s nil t) s))))
(ert-deftest coding-nocopy-ascii ()
"Check that the NOCOPY parameter works for ASCII-only strings."
(let* ((uni (apply #'string (number-sequence 0 127)))
(multi (string-to-multibyte uni)))
(dolist (s (list uni multi))
(dolist (coding '(us-ascii iso-latin-1 utf-8))
(should-not (eq (decode-coding-string s coding nil) s))
(should-not (eq (encode-coding-string s coding nil) s))
(should (eq (decode-coding-string s coding t) s))
(should (eq (encode-coding-string s coding t) s))))))
;; Local Variables:
;; byte-compile-warnings: (not obsolete)
;; End: