GCC stuff

Preprocessing sprintf with literal format string

Latest patch:

Performance testing

To test the performance of various approaches, I've used a small program that calls sprintf(buf, "%d-%d-%d", a, b, c) in a loop 10 million times.

test program	user time spent	Description
sprintf-glibc	5.20	vanilla glibc call
sprintf-linux	3.16	sprintf implementation from the Linux kernel, version 2.6.20.4
sprintf-linux-new	3.04	sprintf implementation from the Linux kernel, version 2.6.23-rc9
sprintf-gcc	0.82	normal call to sprintf, but compiled with latest GCC trunk with the above patch applied
sprintf-linux-nop	1.04	sprintf implementation from Linux 2.6.23-rc9, but the call to "number" subfunction commented out. Note that this produces wrong results. The purpose this test is to demonstrate the overhead of just parsing the format string.

Here are all the test programs and a Makefile to compile them, if you want to test them yourself. To compile sprintf-gcc, you'll need to download latest GCC sources from the SVN repository, apply the patch and compile, and modify the paths in the Makefile.

TODO:

handle printf/fprintf and other variants as well
do we need something in expand_builtin_sprintf as well?
control the feature with the -O option
handle more conversion specs
where to put the primitive functions? glibc? add them to object file? inline?

Heikki Linnakangas <heikki.linnakangas@iki.fi.nospam>
Updated: 8.10.2007