* Ada decimal math, an example (or counterexample)
@ 1988-07-01 17:54 Norman Cohen
0 siblings, 0 replies; 3+ messages in thread
From: Norman Cohen @ 1988-07-01 17:54 UTC (permalink / raw)
Sam Harbaugh expects the addition in
my_dime : dollar_type :=
0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01;
-- 1 2 3 4 5 6 7 8 9 10
to be performed using universal_real addition rather than dollar_type
addition. Actually, it is performed using dollar_type addition: Each
real literal is implicitly converted to dollar_type and the ten resulting
dollar_type values are summed.
If Sam had written
my_dime : constant :=
0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01;
then exact universal_real addition would have been performed.
The Ada rule is that conversion takes place only at the bottom of the
expression tree: Only numeric literals, named numbers, and attributes
with universal results are convertible.
The rule is given in RM paragraph 4.6(15). Paragraph 4.6(20) provides
enlightening examples.
Norman Cohen
IBM Research
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Ada decimal math, an example (or counterexample)
@ 1988-07-06 18:48 Gary Morris @flash
0 siblings, 0 replies; 3+ messages in thread
From: Gary Morris @flash @ 1988-07-06 18:48 UTC (permalink / raw)
>
> type dollar_type is delta 0.01 range 0.00..1000.00;
> ...
> my_dime : dollar_type :=
> 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01;
> ...
These calculations are done using the dollar_type which has a 'small of
0.0078125. For the use you are making of this type, you should use a rep
spec to make 'small be the same as the delta. The TeleSoft TeleGen2
compiler supports this:
type dollar_type is delta 0.01 range 0.00..1000.00;
for dollar_type'small use 0.01;
With the rep spec our Sun Ada 1.1 compiler produces the "expected" results:
-- my_dime is worth 0.10
--your_dime is worth 0.10
Without the rep spec our Sun Ada 1.1 compiler does the computation using
a 'small of 0.0078125 yielding 0.078125, which is rounded to 0.08 for
output:
-- my_dime is worth 0.08
--your_dime is worth 0.08
Gary Morris UUCP: ucbvax!ucsd!telesoft!garym
TeleSoft, San Diego telesoft!garym@ucsd.edu
(619) 457-2700 ARPA: ucsd!telesoft!garym@ucbvax.ARPA
^ permalink raw reply [flat|nested] 3+ messages in thread
* Ada decimal math, an example (or counterexample)
@ 1988-06-30 21:53 CONTR47
0 siblings, 0 replies; 3+ messages in thread
From: CONTR47 @ 1988-06-30 21:53 UTC (permalink / raw)
with text_io; use text_io;
procedure decimal is
type dollar_type is delta 0.01 range 0.00..1000.00;
package decimal_io is new fixed_io(dollar_type); use decimal_io;
my_dime : dollar_type :=
0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01 + 0.01;
-- 1 2 3 4 5 6 7 8 9 10
your_dime : dollar_type := 0.0;
begin
for i in 1..10 loop
your_dime := your_dime + 0.01;
end loop;
put("-- my_dime is worth "); put ( my_dime ); new_line;
put("--your_dime is worth "); put ( your_dime ); new_line;
end decimal;
-- Janus 2.0.2 prints:
-- my_dime is worth 0.08 (Janus apparently isn't doing universal math)
--your_dime is worth 0.08
-- Alsys v3.2 prints:
-- my_dime is worth 0.10
-- your_dime is worth 0.08
-- Verdix (VADS Version 5.41 ) prints:
-- my_dime is worth 0.10
-- your_dime is worth 0.07 (apparently it truncates on I/O)
--Dec version 1.3 prints:
-- my_dime is worth 0.08 (apparently isn't doing universal math)
-- your_dime is worth 0.08
--Since Dec says my_dime is worth 0.08 I now question whether
--Universal math is required for the initialization. Maybe
--only Alsys is doing the my_dime computation at compile time
--and therefore using Universal math and the others are doing
--it at run time using model numbers. What do you experts say?
--I formally withdraw my suggestion to perform computation
--in the declarative region in order to have it done by
--universal math. Sigh.
--regards,sam harbaugh
----------------------
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