RE: Calling some vendor "C" code from RPGIV

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Thanks Simon,  I think I get you and will give it a shot.

-----Original Message-----
From: Simon Coulter [mailto:shc@flybynight.com.au]
Sent: Wednesday, July 10, 2002 4:46 PM
To: c400-l@midrange.com
Subject: Re: [C400-L] Calling some vendor "C" code from RPGIV



Hello Tom,

You wrote:
>void sha1( void *buf, unsigned long len, unsigned long *iv, unsigned long
>digest[5] )
>and I'm trying to figure out the prototype.
>D Sha1            PR
>D  Buffer                    32767a   Const Options(*Varsize)
>D  BfrLength                    10i 0 Const
>D  IV                           10i 0 Const
>D  Digest                       10i 0 Dim(5)

Based on the above C prototype I would code:
D Sha1            PR
D  Buffer                    32767a   Const Options(*Varsize)
D  BfrLength                    10U 0 Value
D  IV                           10U 0
D  Digest                       10U 0 Dim(5)

>So I guess I do something RPGIV like:
>Sha1( PIN# : %len(PIN#) : ???? : Digest );
>where Digest is an RPGIV array of 8a dim(5)?

No.  According to the above C prototype, Digest is an array of unsigned
long integers (i.e., 10U 0) with 5 elements.

>I have no idea what the *buf and *iv things mean.

You have to read the complete definition.  The * means a pointer but you
have to read the stuff to the left of the * to know what data type the
pointer references.

void *buf means a pointer to a buffer i.e., the address of some storage of
arbitrary length.

unsigned long *iv means a pointer to an unsigned long integer.

When C uses pointers to integers it usually means the called
procedure/function intends to change the value in that storage.  Hence the
lack of CONST on my prototype definition above.

You also need to 'know' that C expects most things to be passed by value
hence the use of VALUE on my prototype.  Arrays are passed by reference.
Pointers are passed by value but that is the same as a variable passed by
reference hence the use of a large *VARSIZE buffer rather than a pointer.
It is not apparent from the C prototype whether the C procedure intends to
alter the contents of the buffer (i.e., what does sha_update do with the
buffer?) but given the C prototype it would be possible to change the
contents of buffer so you probably ought to remove CONST from the buffer
definition.  (To make it clear that the contents of buffer is not to be
changed they should have coded const void * buf or better const void *
const buf).

If this isn't clear then let me know and I'll do a Prototypes-101 append
explaining how to transform the supplied C prototype of sha1 into RPG IV.

Regards,
Simon Coulter.
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