nelson_p@apollo.HP.COM (Peter Nelson) (02/11/90)
I've been using the Zortech C++, Version 2.0 compiler
to write a CA (Cellular Automata) tool, which I've
discussed elesewhere on Usenet, for my PC. I'm not
currently taking advantage of its C++ features -- I
thought I would do that later as an educational exercise--
for now I'm using vanilla C.
But I DO need to handle large, 2-dimensional arrays
and Zortech seems to have a problem with that.
The problem is that my total global memory will exceed
64K, although I am grudgingly willing to settle for having
no *one* array exceed that size if that would help here.
Those who are unfortunate enough to be familiar with 80x86
architecture are well aware of the weird, segmented addressing
scheme that those computers use and how this has forced compiler
makers to create bizarre "memory models" to handle it. Zortech
offers two memory models (Large and Compact) which allow the
program to access global or static memory which may exceed 64K.
(They don't offer a "Huge" memory model, as Microsoft does).
But they do not apparently offer any way to access memory > 64K
AS 2-DIMENSIONAL ARRAYS, which is the logical data structure
for cellular automata. All I apparently can do with their
product is malloc a chunk of space and access it via pointers.
If I wanted to do pointer arithmetic all over the place I would
use Assembler! Zortech C/C++ is allegedly a high-level language
but their manual describes this as a "limitation" of their product.
I would call it a bug.
I did call their Arlington office and spoke to several people
who were unable to provide a workaround but they did suggest that
the legendary Walter Bright, who has been known to appear in
the netherworld of Usenet, might have some ideas about this.
If anyone has some ideas on this I would appreciate it if they
would send me email, since for the last week or so we have not been
getting new Usenet postings at this site.
---Peter
PS- The Arlington office mentioned a Zortech BBS in Washington
state which I dialed and got a carrier, but for some reason
I couldn't talk to it. My modem *thought* it made a connection
but nothing I typed got echoed, I didn't get any characters from
it, and although it never hung up on me, eventually I got bored
and hung up on it. Comments, anyone?
nelson_p@apollo.HP.COM (Peter Nelson) (02/12/90)
I received a number of responses to my query about how to
allocate large, global 2-dimensional arrays in Zortech C++,
where no individual array would be > 64K but the total
space involved for all of them would exceed 64K. One
of my requirements is that I can access them as 2-dimensional
arrays and not have to access them via pointer arithmetic.
Most of them involved extensive use of malloc and pointers.
The whole idea of using a high-level language in the first
place is to make the architectural ideosyncracies of the
machine INVISIBLE to the user and allow the user to express
the program in terms of his problem. In my case that means
2 dimensional arrays.
There is no **technical reason** why the Zortech compiler
can't allow you to allocate arbitrarily large amounts of
global memory, up to the limitations of available RAM, and
simply manipulate the DS register to access it. Sure, there's
more overhead, but the manual already warns the user that the
use of the C or L memory models is less efficient, so we
must presume that the user is willing to pay that price.
On a virtual memory machine I know that if I allocate
an array that exceeds the size of my available physical
RAM I'm going to pay a huge performance penalty due to
paging. But if I'm willing to live with that then I
don't have to write my program any differently.
80x86 machines have their segmented architecture but virtually
ALL computers have lots of addressing modes and different length
address or offset registers, with different numbers of ticks
required to execute them. But our C compilers here at work don't
ask me what addressing modes or register sizes to use. Hell,
I don't have to even worry about rewriting my program when
I go from, say, a 68030 platform to an Apollo DN10000 (RISC).
If I *want* to tune the program I have large selection of
options, but I'm not forced to use them.
With the Zortech product, as well as some other DOS products,
I apparently have to return to those "golden days of yesteryear"
and be a hobbyist hacker again. And I thought I'd paid those
dues and graduated to software adulthood already.
---Peter
bright@Data-IO.COM (Walter Bright) (02/13/90)
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: Zortech "limitation"
Summary:
Expires:
References: <48910321.20b6d@apollo.HP.COM>
Sender:
Reply-To: bright@Data-IO.COM (Walter Bright)
Followup-To:
Distribution: usa
Organization: Data I/O Corporation; Redmond, WA
Keywords:
In article <48910321.20b6d@apollo.HP.COM> nelson_p@apollo.HP.COM (Peter Nelson) writes:
< But I DO need to handle large, 2-dimensional arrays
< and Zortech seems to have a problem with that.
< The problem is that my total global memory will exceed
< 64K, although I am grudgingly willing to settle for having
< no *one* array exceed that size if that would help here.
Instead of having:
int array[N][M]; /* array of N columns */
try:
int (*array[N])[M]; /* array of N pointers to columns */
/* Create the columns */
for (i = 0; i < N; i++)
array[i] = (int (*)[M])malloc(sizeof(int [M]));
#define array_access(i,j) ((*array[i])[j])
(I wrote this off the cuff, so it may have a syntax error, but I've done
this before and it works fine. In fact, it is *faster* than doing huge
arithmetic.)
< If I wanted to do pointer arithmetic all over the place I would
< use Assembler! Zortech C/C++ is allegedly a high-level language
< but their manual describes this as a "limitation" of their product.
< I would call it a bug.
There's no assembler in the example above. One man's bug is another's feature.
C is not a high-level language, it's a "portable assembler", thus the
limitations and capabilities of the underlying instruction set are
reflected in the source code. I occasionally get "bug" reports that the
compiler does not make the PC look like a VAX.
< PS- The Arlington office mentioned a Zortech BBS in Washington
< state which I dialed and got a carrier, but for some reason
< I couldn't talk to it.
The phone number is (206) 822-6907. The BBS works fine, and has been for
years. It gets heavy use. It uses a Hayes 2400 baud external modem. I
suggest you try again.mark@Jhereg.Minnetech.MN.ORG (Mark H. Colburn) (02/13/90)
In article <48910321.20b6d@apollo.HP.COM> nelson_p@apollo.HP.COM (Peter Nelson) writes: > But they do not apparently offer any way to access memory > 64K > AS 2-DIMENSIONAL ARRAYS, which is the logical data structure > for cellular automata. All I apparently can do with their > product is malloc a chunk of space and access it via pointers. > If I wanted to do pointer arithmetic all over the place I would > use Assembler! Zortech C/C++ is allegedly a high-level language > but their manual describes this as a "limitation" of their product. > I would call it a bug. Well, it is not really a bug. You can malloc the huge hunk of memory and then treat it as a two dimensional array of whatever form you like (or three, or four dimensional as well). The compiler will do the pointer arithmetic for you. It would have to do so regardless of how you declared the array. The following section of code should do what you want: #include <stdio.h> #include <stdlib.h> /* malloc prototype here */ typedef unsigned char my_array_type; my_array_type **my_array; int i; int j; int main() { if ((my_array = malloc((size_t)(WIDTH * HEIGHT))) == NULL) { printf("Malloc error"); exit(1); } for (i = 0; i < HEIGHT; i++) { for (j = 0; j < WIDTH; j++) { my_array[i][j] = i*j; printf("%6d "); } printf("\n"); } } The initialization section is contrived, and is there simply to show that you can use the my_array pointer as if it were declared as: my_array_type my_array[WIDTH][HEIGHT]; With no problems. The code example assumes ANSI C, otherwise the malloc call should be cast correctly, but since Zortech is ANSI Compliant, you shouldn't have any problems. The my_array_type is defined just to show that you could use virtually any type for the array that you want, including structures, etc. -- Mark H. Colburn mark@Minnetech.MN.ORG Open Systems Architects, Inc.
williams@umaxc.weeg.uiowa.edu (Kent Williams) (02/13/90)
C'mon, dude. We all know the Intel Processors are brain-damaged. This is
pretty old news. Besides, what's the big deal about calling malloc to build
a >64K two-dimensional array? On the PC, the code generated is going to
be better than if Walter did you the 'favor' of giving you huge arrays.
So you just do something like:
something **huge_array = (something **)malloc(N*sizeof(something *));
for(int i = 0; i < N; i++)
huge_array[i] = (something *)malloc(sizeof(something)*M);
And the normal array subscripting semantics apply, TRANSPARENTLY, AS THOUGH
THIS WERE A LANGUAGE FEATURE PUT THERE TO MAKE THINGS EASY FOR THE PROGRAMMER!
How about that?
In this case the code generated is something like:
something& access(i,j) {
basereg = *(huge_array + i)
indexreg = j * sizeof(something);
return *(basereg + indexreg);
}
Whereas if you had huge arrays its something like:
something& access(i,j) {
basereg = hideous_segment_calculation(huge_array,i);
indexreg = hideous_segment_calculation(basereg,j);
}
Which would you rather have under the hood?
--
Kent Williams "What's an Address Bus? How do Icons work?"
williams@umaxc.weeg.uiowa.edu -- Advertisement for Time-Life Books jeffa@hpmwtd.HP.COM (Jeff Aguilera) (02/13/90)
> I occasionally get "bug" reports that the > compiler does not make the PC look like a VAX. My PC is faster, smaller, and a lot cheaper than a (certain well-known...) VAX. If your compiler transmogrifies my computer I'll be really mad ;-) regards, jeffa
nelson_p@apollo.HP.COM (Peter Nelson) (02/16/90)
bright@Data-IO.COM (Walter Bright) posts... >< If I wanted to do pointer arithmetic all over the place I would >< use Assembler! Zortech C/C++ is allegedly a high-level language >< but their manual describes this as a "limitation" of their product. >< I would call it a bug. > >There's no assembler in the example above. One man's bug is another's feature. >C is not a high-level language, it's a "portable assembler", thus the >limitations and capabilities of the underlying instruction set are >reflected in the source code. I occasionally get "bug" reports that the >compiler does not make the PC look like a VAX. I don't think its the job of the compiler to make one brand of com- puter look like another, whether it's a case of a PC looking like a VAX or a Mac looking like a Sun. Rather, it is to make all computers look like the same virtual machine, in this case a "C" computer. The key word in Mr. Bright's above paragraph is "portable". Languages achieve portability by allowing the programmer to write his code in a way which is not dependent on the architectual whims or affectations of a particular hardware vendor. In order to achieve this it is necessary to obscure the underlying features of the target machine's architecture. In principle I ought to be able to take a program which I wrote on my HP/Apollo DN10000 and port it to my PC or my friend's Mac or my wife's DG Aviion just by recompiling it. This is NOT achieved by making the Aviion, PC, or Mac look like a DN10000. In practice, of course, mapping C to a particular architecture may be much harder in some cases than others. 80x86's certainly offers some challenges to the compiler writer and the programmer may sacrifice some performance to have the architecture hidden from him, but that should be his choice. In today's heterogeneous environments, portability is becoming increasingly important and I may prefer to take a performance hit if it means not having to rewrite my code when I go from an Apollo to a PC. ---Peter PS- A philosophical point: The average computer has become vastly more powerful in recent years. An XT might be a 0.5 MIPS machine, but 386's are running 5-7 MIPS and '486's are claiming 10-15 MIPS. Motorola is claiming 20 MIPS for their 25 MHz 68040 and say they will have a 50MHz part out in a year. In such an environment productivity, ease of maintenance, readability of code and portability of code may outweigh the small loss of efficieny suffered by having the compiler generate some DS-register manipulations behind the scenes, however much a hack this might seem to the compiler-writer. Memory and CPU cycles are a LOT cheaper than they used to be and our priorities should reflect this.
bright@Data-IO.COM (Walter Bright) (02/17/90)
In article <48aa63d6.20b6d@apollo.HP.COM> nelson_p@apollo.HP.COM (Peter Nelson) writes: < Languages achieve portability by allowing the programmer to < write his code in a way which is not dependent on the architectual < whims or affectations of a particular hardware vendor. To achieve portability you must code to the common denominator between all the platforms. Note that I don't know of any reasonable method to implement on the 8086 things like: func() { char array[70000]; ... } The 8086 hardware simply doesn't support it. < In principle I ought to be < able to take a program which I wrote on my HP/Apollo DN10000 < and port it to my PC or my friend's Mac or my wife's DG Aviion just < by recompiling it. This is NOT achieved by making the Aviion, PC, < or Mac look like a DN10000. Unless you adhere to portable constructs, making the PC look like a DN10000 is the only way. Zortech's philosophy is to allow the developer to create a PC product with maximum speed/size efficiency. In order to do this, the behavior of the compiler matches the behavior of the underlying machine. Fighting the compiler and the PC environment is counterproductive to producing a PC application. Obviously, you disagree with this point of view. I suspect that with your philosophy, Smalltalk is a better language for you than C++.