Date: Wed, 29 Oct 2014 22:39:34 +0800 From: "bycn82" <bycn82@gmail.com> To: <freebsd-ipfw@freebsd.org> Subject: performance of the swtich/case statements Message-ID: <009101cff386$29c30e50$7d492af0$@gmail.com>
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Hi All, It is using the switch/case statement to make the code clear in the implementation, so it reminded me the question which I want to ask when I read the source of ipfw for the first time. It is about the performance of the switch/case statement. Sure the code of this table feature are running in the user-land, so there is no performance concern here, But my question is the switch/case statements in the 2 loops. I am not a C programmer, so I am not clear how the switch/case will be optimized by the compiler in FreeBSD. But I used to write a compiler by myself and I use a hash table to handle all the conditions in the case statements because my compiler don't care about performance!, But in C it is different, the case statement can only accept "int" values, so I don't think it will use hash or what , it should be directly use an array(), So whether it can be optimized it depends on the conditions in the switch/case statements, and I noticed that the cases statement in the 2 loops are not arranging the opcode in running number, so does the compiler smart enough to optimize it? Regards, Bycn82 From: bycn82 [mailto:bycn82@gmail.com] Sent: Wednesday, 29 October, 2014 10:17 PM To: 'freebsd-ipfw@freebsd.org' Subject: ipfw table features Hi, Finally got some time to read the new implementation of table feature. Compare to the previous code, it is much more clear now, Well done! Regards, Bycn82
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