From: Dmitry Antipov <dmantipov@yandex.ru>
To: Emacs development discussions <emacs-devel@gnu.org>
Subject: [RFC] temporary Lisp_Strings
Date: Tue, 02 Sep 2014 16:55:57 +0400 [thread overview]
Message-ID: <5405BE5D.1090003@yandex.ru> (raw)
[-- Attachment #1: Type: text/plain, Size: 297 bytes --]
I'm thinking about temporary Lisp_Strings on C stack (allocated with alloca).
Simple implementation (with no check whether it fits on stack) and a few use
cases attached. Among others, the question is: is there a way to make sure
that an address returned by alloca fits in Lisp_Object?
Dmitry
[-- Attachment #2: alloca_string.patch --]
[-- Type: text/x-patch, Size: 2374 bytes --]
=== modified file 'src/fileio.c'
--- src/fileio.c 2014-09-02 11:41:22 +0000
+++ src/fileio.c 2014-09-02 11:47:45 +0000
@@ -1179,11 +1179,11 @@
char newdir_utf8[MAX_UTF8_PATH];
filename_from_ansi (newdir, newdir_utf8);
- tem = build_string (newdir_utf8);
+ tem = alloca_string (newdir_utf8);
}
else
#endif
- tem = build_string (newdir);
+ tem = alloca_string (newdir);
newdirlen = SBYTES (tem);
if (multibyte && !STRING_MULTIBYTE (tem))
{
@@ -1215,7 +1215,7 @@
/* `getpwnam' may return a unibyte string, which will
bite us since we expect the directory to be
multibyte. */
- tem = build_string (newdir);
+ tem = alloca_string (newdir);
newdirlen = SBYTES (tem);
if (multibyte && !STRING_MULTIBYTE (tem))
{
@@ -1249,7 +1249,7 @@
adir = NULL;
else if (multibyte)
{
- Lisp_Object tem = build_string (adir);
+ Lisp_Object tem = alloca_string (adir);
tem = DECODE_FILE (tem);
newdirlen = SBYTES (tem);
@@ -1350,7 +1350,7 @@
getcwd (adir, adir_size);
if (multibyte)
{
- Lisp_Object tem = build_string (adir);
+ Lisp_Object tem = alloca_string (adir);
tem = DECODE_FILE (tem);
newdirlen = SBYTES (tem);
=== modified file 'src/lisp.h'
--- src/lisp.h 2014-09-02 06:49:40 +0000
+++ src/lisp.h 2014-09-02 12:31:01 +0000
@@ -4459,6 +4459,25 @@
memcpy (alloca (SBYTES (string) + 1), \
SSDATA (string), SBYTES (string) + 1)
+/* Create temporary Lisp_String. Use alloca and do not disturb GC. */
+
+#define alloca_string(str) \
+ ({ Lisp_Object string; \
+ struct Lisp_String *s; \
+ ptrdiff_t nchars, nbytes, size = strlen (str); \
+ parse_str_as_multibyte ((const unsigned char *) str, \
+ size, &nchars, &nbytes); \
+ s = alloca (sizeof *s + nbytes + 1); \
+ s->data = (unsigned char *) s + sizeof (*s); \
+ memcpy (s->data, str, nbytes); \
+ s->data[size] = '\0'; \
+ s->intervals = NULL; \
+ if (nbytes == nchars || nbytes != size) \
+ s->size = size, s->size_byte = -1; \
+ else \
+ s->size = nchars, s->size_byte = nbytes; \
+ XSETSTRING (string, s); string; })
+
/* Set up the name of the machine we're running on. */
extern void init_system_name (void);
next reply other threads:[~2014-09-02 12:55 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-02 12:55 Dmitry Antipov [this message]
2014-09-02 13:21 ` [RFC] temporary Lisp_Strings Andreas Schwab
2014-09-02 13:47 ` Dmitry Antipov
2014-09-02 14:14 ` Andreas Schwab
2014-09-02 15:00 ` Eli Zaretskii
2014-09-02 14:00 ` Stefan Monnier
2014-09-02 15:13 ` Dmitry Antipov
2014-09-02 17:32 ` Stefan Monnier
2014-09-03 10:23 ` Benchmarking temporary Lisp objects [Was: Re: [RFC] temporary Lisp_Strings] Dmitry Antipov
2014-09-03 13:14 ` Stefan Monnier
2014-09-03 14:39 ` Paul Eggert
2014-09-03 15:39 ` Dmitry Antipov
2014-09-03 16:42 ` Paul Eggert
2014-09-03 17:47 ` Stefan Monnier
2014-09-03 18:00 ` Paul Eggert
2014-09-04 4:59 ` Dmitry Antipov
2014-09-04 5:13 ` Paul Eggert
2014-09-04 5:51 ` Dmitry Antipov
2014-09-04 6:45 ` Paul Eggert
2014-09-04 13:11 ` Stefan Monnier
2014-09-04 13:37 ` Dmitry Antipov
2014-09-04 14:46 ` Dmitry Antipov
2014-09-04 16:03 ` Paul Eggert
2014-09-05 4:00 ` Dmitry Antipov
2014-09-05 4:24 ` Stefan Monnier
2014-09-05 9:28 ` Dmitry Antipov
2014-09-05 7:15 ` Paul Eggert
2014-09-05 9:16 ` Dmitry Antipov
2014-09-05 14:35 ` Paul Eggert
2014-09-05 15:35 ` Stefan Monnier
2014-09-08 10:33 ` Dmitry Antipov
2014-09-08 12:01 ` Dmitry Antipov
2014-09-08 13:30 ` Stefan Monnier
2014-09-08 12:44 ` Stefan Monnier
2014-09-08 13:30 ` Stefan Monnier
2014-09-02 14:37 ` [RFC] temporary Lisp_Strings Paul Eggert
2014-09-02 15:24 ` Dmitry Antipov
2014-09-02 15:28 ` Dmitry Antipov
-- strict thread matches above, loose matches on Subject: below --
2014-09-02 12:56 Dmitry Antipov
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