Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!ftanaka
From: ftanaka@Apple.COM (Forrest Tanaka)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Script Manager 68881 woes
Keywords: Script Mgr, mc68881,c++
Message-ID: <48509@apple.Apple.COM>
Date: 26 Jan 91 07:20:35 GMT
References: <15933@reed.UUCP>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 75

bowman@reed.UUCP (Eric Bowman) writes:

>I'm trying to write a function in C++ to convert between floating point
>and text using the script manager.  Easy enough:
>
>void plot::DecToString(double theNum,Str255 theString)
>{
>	extended temp;
>
>	temp = (extended) theNum;
>	FormatX2Str(temp,&myNumFormat,&myNumberParts,theString);
>}
>
>This works fine, except when the 68881 compiler option is on.
>
>The problem seems clear -- 96 bits versus 80 bits for the length
>of an extended.


Your analysis of this problem is right on the money.  You can convert between
80-bit and 96-bit extended numbers by using a couple of routines declared in
MPW's SANE.h header file that are called x96tox80 and x80tox96.  The
extended80 and extended96 types aren't equivalent to the extended type as far
as the C compiler is concerned, so you have to redeclare FormatX2Str and
FormatStr2X to take these types. You can do this like this:
 
pascal FormatStatus FormatX2Str (extended80            x,
                                 const NumFormatString *myCanonical,
                                 const NumberParts     *partsTable,
                                 Str255                outString)
    = {0x2F3C,0x8210,0xFFE8,0xA8B5};
 
pascal FormatStatus FormatStr2X (const Str255          source,
                                 const NumFormatString *myCanonical,
                                 const NumberParts     *partsTable,
                                 extended80            *x)
    = {0x2F3C,0x8210,0xFFE6,0xA8B5};
 
Call these routines instead of the originals. To call FormatX2Str80, all you
have to do is this:
 
extended        x; /* 96-bit extended number */
NumFormatString myCanonical;
NumberParts     partsTable;
Str255          outString;
 
result = FormatX2Str80 (x96tox80 (x), &myCanonical, &partsTable, outString);
 
Calling FormatStr2X80 is just slightly more complicated because the extended
number is passed by reference:
 
extended        x;   /* 96-bit extended number */
extended80      x80; /* 80-bit extended number */
Str255          source;
NumFormatString myCanonical;
NumberParts     partsTable;
 
x80 = x96tox80 (x);
result = FormatStr2X80 (theString, &myCanonical, &partsTable, &x80);
x = x80tox96 (x80);


--Forrest



>bobo
>bowman@reed.{bitnet,UUCP,edu}
>...!tektronix!reed!bowman


-- 
Forrest Tanaka                                    AppleLink: TANAKA
Graphics/Toolbox Developer Technical Support       Internet: ftanaka@apple.com
Apple Computer, Inc.                                  Phone: 408 974-1243