From: David Guillen Fandos <david@davidgf.es>
To: musl@lists.openwall.com
Subject: Do not use 64 bit division if possible
Date: Sat, 25 Nov 2017 21:52:06 +0100 [thread overview]
Message-ID: <424674f0-8460-7807-7366-a87d8588e8bc@davidgf.es> (raw)
Hey there,
Just noticed that my binary was getting some gcc functions for integer
division in some places coming from musl. I checked and it seems that,
even though musl assumes PAGE_SIZE is always power of two, that we
divide by it instead of using shifts for that. This results in extra
overhead and slow division on platforms that do not have a 64 bit
divider (even the ones that do have 32 bit divider).
So I propose a patch here, let me know what you people think about.
David
diff --git a/src/conf/sysconf.c b/src/conf/sysconf.c
index b8b761d0..aa9fc9d1 100644
--- a/src/conf/sysconf.c
+++ b/src/conf/sysconf.c
@@ -4,6 +4,7 @@ long sysconf(int name)
#include <sys/sysinfo.h>
#include "syscall.h"
#include "libc.h"
+#include "atomic.h"
#define JT(x) (-256|(x))
#define VER JT(1)
@@ -206,7 +206,7 @@ long sysconf(int name)
if (name==_SC_PHYS_PAGES) mem = si.totalram;
else mem = si.freeram + si.bufferram;
mem *= si.mem_unit;
- mem /= PAGE_SIZE;
+ mem >>= (unsigned)(a_ctz_l(PAGE_SIZE));
return (mem > LONG_MAX) ? LONG_MAX : mem;
case JT_ZERO & 255:
return 0;
next reply other threads:[~2017-11-25 20:52 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-25 20:52 David Guillen Fandos [this message]
2017-11-25 23:15 ` Michael Clark
2017-11-25 23:46 ` David Guillen Fandos
2017-11-25 23:53 ` Rich Felker
2017-11-26 0:10 ` Michael Clark
2017-11-26 0:49 ` David Guillen Fandos
2017-11-26 0:59 ` Rich Felker
2017-11-26 1:12 ` David Guillen Fandos
2017-11-26 1:23 ` Rich Felker
2017-11-26 1:40 ` David Guillen Fandos
2017-11-26 0:49 ` Rich Felker
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