[M3devel] INTEGER vice INT32

[Tony Hosking]

But we *do* have explicit types in Modula-3.  Subranges and BITS FOR let us pretty much do everything we want (the current implementation restrictions are in using underlying in-memory representations for subranges that round to the nearest byte size).


Antony Hosking | Associate Professor | Computer Science | Purdue University
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On 17 Dec 2009, at 11:18, Peter Eiserloh wrote:

> Hi Tony,
> 
> Both Jay, and yourself have valid points.
> 
> One can classify the two kinds of types, as implicit, and 
> explicit.  
> 
> More specifically, INTEGER is implicit, and is useful for
> in-memory representation.  This was especially important 
> when machine registers were very different between machines.
> Very few remember the days of 18-bit words, with 9-bit 
> bytes (thank you!).  An implicit type is very useful, 
> when you are not worried about external representation
> and all one needs is the logical behavior of the type,
> independent of the particular machine on which one may
> currently be.
> 
> Explicit types are much more useful, if not imperative, 
> when defining data types for external storage (in files, 
> or network protocols).
> 
> For binary file IO many people take a naive approach, and
> simply overlay a data structure onto the file stream.  
> This ignores the potential difference in sizes of implicit
> types, and their endianess.   A more careful method of
> doing binary files, is to distinguish the external from
> the internal representation, and have procedures to do
> the IO a field at a time.  See binIO.
> 
> Back in the late 1980's, and early 1990s, I had an Amiga 
> computer, and had two different "C" compilers: Aztec, C
> and SAS/C.  The Aztec compiler int was 16-bits, whereas 
> the SAS/C int was 32 bits.  As you can imagine this caused 
> all sorts of havoc.  The Amiga system includes were 
> rewritten with somewhat more explicit types. These were 
> macros such as ULONG, SLONG, USHORT, SSHORT, UBYTE, and 
> SBYTE. 
> 
> This illustrates the importance of explicit types.
> Both implicit and explicit types have their place.
> 
> 
> Peter
> 
> 
> 
> Date: Wed, 16 Dec 2009 20:10:14 -0500
> From: Tony Hosking <hosking at cs.purdue.edu>
> Subject: Re: [M3devel] Oops, forgot to ask
> To: Jay K <jay.krell at cornell.edu>
> Cc: m3devel <m3devel at elegosoft.com>
> Message-ID: <EF60618E-7AE3-4FF9-A805-5B8B83B369E2 at cs.purdue.edu>
> Content-Type: text/plain; charset="us-ascii"
> 
>> On 16 Dec 2009, at 19:52, Jay K wrote:
>> 
>>> "0..LAST(LONGINT)" having varying meaning...like when INTEGER is > 64 
>> bits, then LONGINT=INTEGER, and we anticipate 128 bit INTEGER?
>>> 
>>> 
>>> See..LONGINT is only useful in this brief period where we still have 32bit INTEGER.
>>> (Actually it would have been useful long ago.)
>> 
>> LONGINT could be 128 bits for all its definition cares.  It is just 
>> something usually (not always) bigger than an INTEGER.
>> 
>>> I really think "long" is a dumb name..
>>> There should be INT8, UINT8, INT16, UINT16, INT32, UINT32, INT64, 
>> UINT64, and unsigned and signed integers the same size of a pointer, 
>> possibly called INT and UINT, or size_t and ptrdiff_t..
>> 
>> Now these are dumb names because they wire in the size of the value.
>> 
>> In Modula-3 INTEGER is a natural (i.e., word-size) value.
> 
> 
> +--------------------------------------------------------+
> | Peter P. Eiserloh                                      |
> +--------------------------------------------------------+
> 
> 
> 

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