From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <ac08f785796f92ca07123b65fd5d4335@collyer.net>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Clearing venti arena during install
Date: Sun, 26 Mar 2006 16:52:46 -0800
From: geoff@collyer.net
In-Reply-To: <7738cc425fad5f8b56882b45df4fdf6d@swtch.com>
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Furthermore, the check for a zero block can be done pretty cheaply (I
thought about doing this years ago for v7 Unix).  First see if the
first word of the buffer is zero; if so, see if the last word is zero;
if so, run through the buffer a word at a time, stopping at a non-zero
word or end of buffer.

In the common (real-life) case, the test of the first word suffices.
The word-at-a-time scan can be made to run fairly fast, especially if
you have the option of first putting a non-zero word just after the
buffer, so that no explicit bounds test is necessary in the loop.