linux-kernel - Re: why are there some redundant variable definition

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Message-Id: <20100725144447.32f4b5b3.rdunlap@xenotime.net>
Date:	Sun, 25 Jul 2010 14:44:47 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Parmenides <mobile.parmenides@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: why are there some redundant variable definition

On Mon, 26 Jul 2010 05:29:04 +0800 Parmenides wrote:

> Hi,
>   I have read a macro like this
> ++++ include/linux/kernel.h
> 159: #define min_t(type,x,y) \
> 160: ({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
> ++++ net/ipv4/tcp_output.c
> 654: int full_space = min_t(int, tp->window_clamp, tcp_full_space(sk));
> 
> The definitions of __x and __y are somewhat redundant. I think a more
> --

The local variables __x and __y are used so that 'x' and 'y' are not
re-evaluated multiple times.  That could be a problem if either one of
them is an expression.

Anything else?

---
~Randy
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