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From: optimiza@utrcu1.UUCP (Streng)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Problem with my C program [a few general hints about malloc]
Message-ID: <827@utrcu1.UUCP>
Date: 22 Apr 91 19:49:43 GMT
References: <1991Apr21.210056.5685@ccu.umanitoba.ca> <1991Apr22.014758.3846@wam.umd.edu>
Reply-To: optimiza@utrcu1.UUCP (De Leeuw)
Organization: Utwente, Enschede
Lines: 31

In article <1991Apr22.014758.3846@wam.umd.edu> dmb@wam.umd.edu (David M. Baggett) writes:
>If you want to allocate more memory than can be specified in an unsigned int,
>use calloc.  It takes two parameters which are multiplied together to get
>the size of the requested block.  To allocate 128K:
>	p = calloc(128, 1024);
>As a bonus the memory you get is also cleared.  You could write your own
>replacement for Malloc as follows:
>char *
>my_Malloc(size)
>	register long	size;
>{
>	register unsigned	hi, lo;
>	hi = (unsigned) (size >> 16);
>	lo = (unsigned) (size & 0x0000FFFF);
>	return calloc(hi, lo);
>}
Unfortunately, this will not work the way you intend. Assume you want to
Malloc() a block of 65536 bytes. This leads to hi being 1, and lo being
0. This will calloc() a block of 1*0=0 bytes. What you want to do is
factorize size in two factors that are both small enough to be handled
by calloc. I cannot come up right now with an algorithm that does this
both time and memory efficient.
But, there is another possibility. If you are using an ANSI-C compiler,
the standard says that malloc takes an argument of type size_t, but not
that it will be 16 bit. Turbo C, for example, takes a (maybe even
unsigned) long. (unfortunately, this is not the case with MSDOS-TC,
making ports somewhat more difficult)
---
Henk de Leeuw
optimiza@utwente.nl
optimiza%utrcu1.uucp@uunet.uu.net