Subj : QWK .NDX-generating code
To   : All
From : William McBrine
Date : Fri Jan 12 2001 02:59 am

Back when I was starting out in QWK, reading the de facto standard, QWKLAY,
I noticed that the section which presented sample code for dealing with
..NDX files was a little short on the generating end -- there's only one,
real-number-based generating routine, for Pascal, though there are three to
go the other way (one real and one integer-based for Pascal, and one
integer-based for C).

As it happens, I just ran into a guy who was porting his BBS to Linux, and
he was creating the .NDX files incorrectly -- he was using the sample
Pascal code from QWKLAY, but of course, he couldn't use Borland Pascal on
Linux, and the code wasn't quite compatible. So I took the opportunity to
do something I'd meant to do a long time ago, and wrote a more portable,
integer-based routine. My Pascal is rusty, so I wrote it in C first and
ported it. :-)

So then I thought, others might be interested in this code. Here it is; I'm 
putting it in the public domain:

C version:

/* ms is unsigned char ms[4] */

void longtoMSBIN(unsigned long index, unsigned char *ms)
{
	unsigned char exp = '\0';

	if (index) {
		while (!(index & 0x800000L)) {
			exp++;
			index <<= 1;
		}
		index &= 0x7fffffL;
	} else
		exp = 152;

	ms[0] = index & 0xff;
	ms[1] = (index >> 8) & 0xff;
	ms[2] = (index >> 16) & 0xff;
	ms[3] = 152 - exp;
}

Borland-like Pascal version (no reals, no absolutes):

type
 bsingle = array[0..3] of byte;

procedure longtoMSBIN(index: longint; var ms: bsingle);
var
  exp: byte;
begin
  if (index <> 0) then
    begin
      exp := 0;

      while (index and $800000) = 0 do
        begin
          inc(exp);
          index := index shl 1
	end;

      index := index and $7FFFFF;
    end
  else
    exp := 152;

  ms[0] := index and $FF;
  ms[1] := (index shr 8) and $FF;
  ms[2] := (index shr 16) and $FF;
  ms[3] := 152 - exp;
end;

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