I think basic reference information you may be looking for is on page
http://www.merlyn.demon.co.uk/pas-type.htm
------------------------------------------------------------------
real2double from rtl/inc/genmath.inc
------------------------------------------------------------------
function real2double(r : real48) : double;
var
res : array[0..7] of byte;
exponent : word;
begin
{ copy mantissa }
res[0]:=0;
res[1]:=r[1] shl 5;
res[2]:=(r[1] shr 3) or (r[2] shl 5);
res[3]:=(r[2] shr 3) or (r[3] shl 5);
res[4]:=(r[3] shr 3) or (r[4] shl 5);
res[5]:=(r[4] shr 3) or (r[5] and $7f) shl 5;
res[6]:=(r[5] and $7f) shr 3;
{ copy exponent }
{ correct exponent: }
exponent:=(word(r[0])+(1023-129));
res[6]:=res[6] or ((exponent and $f) shl 4);
res[7]:=exponent shr 4;
{ set sign }
res[7]:=res[7] or (r[5] and $80);
real2double:=double(res);
end;
------------------------------------------------------------------
double2real by just mechanically reversed operations
------------------------------------------------------------------
function double2real(d : double) : real48;
var
res : real48;
exponent : word;
begin
{ copy mantissa }
res[0]:=0;
res[1]:=(d[2] shl 3) or (d[1] shr 5);
res[2]:=(d[3] shl 3) or (d[2] shr 5);
res[3]:=(d[4] shl 3) or (d[3] shr 5);
res[4]:=(d[5] shl 3) or (d[4] shr 5);
res[5]:=((d[6] and $f) shl 3) or (d[5] shr 5);
{ copy exponent }
{ correct exponent: }
exponent:= ((d[7] and $7f) shl 4) or ((d[6] shr 4) and $f);
exponent:= exponent +129-1023;
res[0]:= exponent and $ff;
{ set sign }
res[5]:=res[5] or (d[7] and $80);
double2real:=res;
end;
------------------------------------------------------------------
The code above will probably not compile as I use indexes of bytes
bytes on type double.
I don't have a working compiler at this moment.
(FPC is not compiling on OSX)
Would this help you?
Could you write some tests to verify correctness?
Jan
On Sep 20, 2005, at 12:14, Lowell C. Savage wrote:
What I would still like to see is a "Double2Real" which goes in the
opposite direction of the "Real2Double". That way, I can read the
data from the existing files and then save new data back to the same
files. The loss of precision is not important since the numbers we
are using have limitations on their precision that are the limiting
factor (they could probably be "singles" without any trouble--except
that then they wouldn't be compatible with the data files. And
performance isn't really an issue since I'll do any calculations as
doubles (native on x86 platform).
Thanks,
Lowell
Florian Klaempfl <[EMAIL PROTECTED]> wrote, in part:
Lowell C. Savage wrote:
> Has anyone come up with a set of routines for converting between
Turbo
> Pascal's 6-byte "real" format and FPC's real number format?
http://www.freepascal.org/docs-html/rtl/system/real2double.html
Thanks. My apologies for not finding it earlier myself.
> Here's a simple program to demonstrate the issue. In Turbo Pascal
5.5
> (Downloaded from
http://bdn.borland.com/article/0,1410,20803,00.html)
> this code generates a 12-byte file. FPC generates a 16-byte file.
> (Actually, the preprocessor directives shown appear to have no
effect on
What effect should it have?
I would like it to have the same effect whether compiled under Turbo
Pascal 5.5 or under FPC. In both cases, it should write out a 12-byte
file. I don't mind if I have to put in a bunch of ifdefs to define
"real48" and dummy "Double2Real" functions for TP or some such and
redo the assignments to call "Double2Real". In other words, the code
can change--but the data (and data format) is forever. :-)
> this code--not complaining since the docs don't make it appear that
it
> should, just pointing it out.)
The 6 byte real isn't supported by fpc because it isn't handled by the
fpu and thus deadly slow. For maybe 12 years, every new PC has an fpu.
Heavens no! I don't want to do !!CALCULATIONS!! with the 6-byte
reals. I just want to be able to read and store them in the existing
files.
> Program testrec;
> {$IFDEF FPC}
> {$MODE TP}
> {$PACKRECORDS 1}
> {$ENDIF}
> type
> realrec = record
> t1 : real;
> t2 : real;
> end;
>
> var
> realfile : file of realrec;
> r : realrec;
> begin
> r.t1 := 1.0;
> r.t2 := 2.0;
> assign ( realfile, 'c:\r.rfl' );
> rewrite ( realfile );
> write ( realfile, r );
> close ( realfile );
> end.
Lowell C. Savage
[EMAIL PROTECTED]
505-667-6964 (office/msg)
360-961-8965 (cell/msg)
505-667-4341 (shared fax)
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