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From: BOLTHOUSE%MCOPN1@eg.ti.COM
Newsgroups: comp.os.vms
Subject: VAXC RTL "bug"
Message-ID: <8706090257.AA28467@ucbvax.Berkeley.EDU>
Date: Mon, 8-Jun-87 10:34:00 EDT
Article-I.D.: ucbvax.8706090257.AA28467
Posted: Mon Jun  8 10:34:00 1987
Date-Received: Thu, 11-Jun-87 06:13:23 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The ARPA Internet
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it doesn't seem like much of a "bug" to me to have the RTL only read()
64K bytes at a time.  that's a standard VAX number for the size of the
largest string you can manipulate.  look at the VAX architecture manual
at the MOVC5 instruction, for example.  you'll notice that the srclen
and dstlen parts of the instruction are *words*, not longwords.  that's
about 64K.  you can bet RMS (which is what read() eventually calls...)
uses movc5/movc3 to get the stuff read from system space into your P0
space...  also, in the $qio(w) system call, the largest space available
in the IOSB for transfer count is 16 bits (64K...), probably for the
same reasons.

'taint a bug, 'tis a feature.  you wouldn't want RMS to have a tight for
loop to move data around when it can be done with one instruction...

david l. bolthouse
texas instruments defense electronics information systems VAX system suport
(and a bad typist...sigh)
mckinney, texas

ma bell:    214.952.2059
internet:   bolthouse%mcopn1@ti-eg.com