using an FPGA to emulate a vintage computer
in [FPGA]
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From: Charles Richmond on 26 Feb 2010 02:09 glen herrmannsfeldt wrote: > In comp.arch.fpga Scott Lurndal <scott(a)slp53.sl.home> wrote: > (snip, someone wrote) >>>> Q? Why would anyone want to pass an array by value? > >>> Why would anyone want to wrap an array in a struct and pass that by value? > >> Why answer a question with another question? > >> I've never promoted or suggested that one put an array in a struct >> and pass it by value, I frankly think it would be a stupid thing to >> do in a C program. > > It might make sense for a small array. You might have an rgb > array dimensioned [3] instead of three separae variables. > The dimension, I believe, has to be a compile time constant. > > -- glen Heck, for RGB, just use a struct with three variables in it. The dimensions of arrays *used* to have to be compile time constants. Now they have a type of array declared in a function that can have its size depend on an integer passed into the function. (I forget what they call it... maybe a "dynamic array" or something.) -- +----------------------------------------+ | Charles and Francis Richmond | | | | plano dot net at aquaporin4 dot com | +----------------------------------------+
From: Charles Richmond on 26 Feb 2010 02:10 Joe Pfeiffer wrote: > glen herrmannsfeldt <gah(a)ugcs.caltech.edu> writes: > >> In comp.arch.fpga Scott Lurndal <scott(a)slp53.sl.home> wrote: >> (snip, someone wrote) >>>>> Q? Why would anyone want to pass an array by value? >>>> Why would anyone want to wrap an array in a struct and pass that by value? >> >>> Why answer a question with another question? >> >>> I've never promoted or suggested that one put an array in a struct >>> and pass it by value, I frankly think it would be a stupid thing to >>> do in a C program. >> It might make sense for a small array. You might have an rgb >> array dimensioned [3] instead of three separae variables. >> The dimension, I believe, has to be a compile time constant. > > It doesn't. You can use malloc() to allocate an arbitrary-sized buffer, > and then use array syntax to access elements of the buffer. You can > also pass the address of the buffer, and use it like an array in the > called procedure. > > Since C99, you can allocate an array with a variable number of elements > like this: > > printf(" array size >> "); > scanf("%d", &size); > > int awry[size]; But how about the second dimension, Joe??? Can you allocate: int awry2[size][size]; -- +----------------------------------------+ | Charles and Francis Richmond | | | | plano dot net at aquaporin4 dot com | +----------------------------------------+
From: glen herrmannsfeldt on 26 Feb 2010 03:34 In comp.arch.fpga Charles Richmond <frizzle(a)tx.rr.com> wrote: (snip) > Heck, for RGB, just use a struct with three variables in it. Well, the suggestion was an array in a struct. With an array you can loop over it. > The dimensions of arrays *used* to have to be compile time > constants. Now they have a type of array declared in a function > that can have its size depend on an integer passed into the > function. (I forget what they call it... maybe a "dynamic array" > or something.) Yes, but can you do that for an array in a struct. If you pass it in a function call, and it isn't the last argument, how will the called routine know where the other arguments are? I haven't done much with C99 yet. -- glen
From: Ahem A Rivet's Shot on 26 Feb 2010 06:56 On Wed, 24 Feb 2010 11:31:45 -0800 (PST) Eric Chomko <pne.chomko(a)comcast.net> wrote: > On Feb 23, 2:07 pm, "(see below)" <yaldni...(a)blueyonder.co.uk> wrote: > > On 23/02/2010 17:52, in article > > 3ec03225-3a0f-4bcd-9db1-51201d1b3...(a)w12g2000vbj.googlegroups.com, "Eric > > > > Chomko" <pne.cho...(a)comcast.net> wrote: > > > But an ALGOL "activation record" (stack frame) had a lot more than > > > that. As I recall, they copied a lot more just pointers and parameter > > > values. > > > > Just the usual red tape: return address, frame pointer of caller; and > > either a static pointer or some housekeeping for 'display' registers > > (if used) to access non-locals. But bear in mind that in decent > > languages arrays are storable values, so a value array parameter gets > > copied in toto, unlike C. > > > > Are you saying that C doesn't implement true recursion? I have only No, he's saying that C doesn't really implement an array type, the var[offset] syntax is just syntactic sugar for *(var + offset) which is why things like 3[x] work the same as x[3] in C. -- Steve O'Hara-Smith | Directable Mirror Arrays C:>WIN | A better way to focus the sun The computer obeys and wins. | licences available see You lose and Bill collects. | http://www.sohara.org/
From: Michael Wojcik on 26 Feb 2010 13:57
Joe Pfeiffer wrote: > glen herrmannsfeldt <gah(a)ugcs.caltech.edu> writes: >> In comp.arch.fpga Scott Lurndal <scott(a)slp53.sl.home> wrote: >> >>> I've never promoted or suggested that one put an array in a struct >>> and pass it by value, I frankly think it would be a stupid thing to >>> do in a C program. >> It might make sense for a small array. You might have an rgb >> array dimensioned [3] instead of three separae variables. >> The dimension, I believe, has to be a compile time constant. > > It doesn't. You can use malloc() to allocate an arbitrary-sized buffer, > and then use array syntax to access elements of the buffer. You can > also pass the address of the buffer, and use it like an array in the > called procedure. That doesn't work for a pass-by-value array, which is what we're talking about here. You can only pass an array by value in C if it's an array type that's a member of a struct (or union, which is just a special case of struct). -- Michael Wojcik Micro Focus Rhetoric & Writing, Michigan State University |