[M3devel] floating point : problem with Extended.m3

[Tony Hosking]

Are you saying it is broken with EXTENDED=LONGREAL?
That is the current implementation.
This code is heritage.  Not sure I understand all the implications.

On Apr 2, 2011, at 9:28 PM, Mika Nystrom wrote:

> Hello m3devel (mainly Tony),
> 
> I believe I've found a problem with float/Common/Extended.m3.
> 
> Doesn't the code assume that EXTENDED is a multiple of 32 bits wide?
> 
> That does not seem to me to be a safe assumption... in fact I don't
> think it's even safe to round up.  EXTENDED could (and should) be
> 10 bytes wide on most machines.  (I am aware that it is currently
> the same as LONGREAL, but...)
> 
>     Mika
> 
>> UNSAFE MODULE Extended;
>> 
>> IMPORT Word, Int32;
>> 
>> PROCEDURE Equal(a, b: T): BOOLEAN =
>>  BEGIN RETURN a = b END Equal;
>> 
>> 
>> CONST Int32Sz = BYTESIZE(T) DIV BYTESIZE(Int32.T);
>> 
>> TYPE Int32Arr = ARRAY [0..Int32Sz-1] OF Int32.T;
>> 
>> PROCEDURE Hash(a: T): Word.T =
>>  VAR arr := LOOPHOLE(a, Int32Arr); res := 0; BEGIN
>>    FOR i := 0 TO LAST(arr) DO
>>      res := Word.Xor(res, Int32.Hash(arr[i]))
>>    END (* FOR *);
>>    RETURN res
>>  END Hash;
>> 
>> PROCEDURE Compare(a, b: T): [-1..1] =
>>  BEGIN
>>    IF a < b THEN RETURN -1
>>    ELSIF a > b THEN RETURN 1
>>    ELSE RETURN 0
>>    END (* IF *)
>>  END Compare;