Re: Fixed vs float and precision and conversions

["Björn Lundin" <b.f.lundin@gmail.com>]

Den 2020-07-08 kl. 20:21, skrev Niklas Holsti:
> On 2020-07-08 21:10, Björn Lundin wrote:
>> Den 2020-07-08 kl. 20:08, skrev Björn Lundin:
>>
>> The main reason for asking was to see if I got the whole concept
>> of fixed types wrong or not.
>> I did expect
>> 'You should do this or that one-liner' as Niklas proposed.
>> I did not get that to work though
> 
> Oh. What happened when you tried? How did it fail?
> 

I did a test routine like below,
but realized that Float(5.10) - which was converted to Fixed_Type(5.099)
is a valid fixed_type of course.

so
       Fix1 := Fixed_Type(Flt);
or
       Fix2 := Fixed_Type'Round(Flt);

does not really matter, since both may return 5.099
when given 5.10

It is at least not certain that the number expressed in fixed_type is 
one of them in the array below.
And that is my real problem - I think.


   ------------------------------
   type Fixed_Type is delta 0.001 digits 18;
   Bad_odds : exception;
   type Tics_Type is new integer range 1 .. 350;

   ---------------------------
   Global_Odds_Table : array(Tics_Type'Range) of Fixed_Type :=
   (
             1.01,   1.02,   1.03,   1.04,
     1.05,   1.06,   1.07,   1.08,   1.09,
     1.10,   1.11,   1.12,   1.13,   1.14,
     1.15,   1.16,   1.17,   1.18,   1.19,
     1.20,   1.21,   1.22,   1.23,   1.24,
     1.25,   1.26,   1.27,   1.28,   1.29,
     1.30,   1.31,   1.32,   1.33,   1.34,
     1.35,   1.36,   1.37,   1.38,   1.39,
     1.40,   1.41,   1.42,   1.43,   1.44,
     1.45,   1.46,   1.47,   1.48,   1.49,
     1.50,   1.51,   1.52,   1.53,   1.54,
     1.55,   1.56,   1.57,   1.58,   1.59,
     1.60,   1.61,   1.62,   1.63,   1.64,
     1.65,   1.66,   1.67,   1.68,   1.69,
     1.70,   1.71,   1.72,   1.73,   1.74,
     1.75,   1.76,   1.77,   1.78,   1.79,
     1.80,   1.81,   1.82,   1.83,   1.84,
     1.85,   1.86,   1.87,   1.88,   1.89,
     1.90,   1.91,   1.92,   1.93,   1.94,
     1.95,   1.96,   1.97,   1.98,   1.99,
     2.00,   2.02,   2.04,   2.06,   2.08,
     2.10,   2.12,   2.14,   2.16,   2.18,
     2.20,   2.22,   2.24,   2.26,   2.28,
     2.30,   2.32,   2.34,   2.36,   2.38,
     2.40,   2.42,   2.44,   2.46,   2.48,
     2.50,   2.52,   2.54,   2.56,   2.58,
     2.60,   2.62,   2.64,   2.66,   2.68,
     2.70,   2.72,   2.74,   2.76,   2.78,
     2.80,   2.82,   2.84,   2.86,   2.88,
     2.90,   2.92,   2.94,   2.96,   2.98,
     3.00,   3.05,   3.10,   3.15,   3.20,
     3.25,   3.30,   3.35,   3.40,   3.45,
     3.50,   3.55,   3.60,   3.65,   3.70,
     3.75,   3.80,   3.85,   3.90,   3.95,
     4.00,   4.10,   4.20,   4.30,   4.40,
     4.50,   4.60,   4.70,   4.80,   4.90,
     5.00,   5.10,   5.20,   5.30,   5.40,
     5.50,   5.60,   5.70,   5.80,   5.90,
     6.00,   6.20,   6.40,   6.60,   6.80,
     7.00,   7.20,   7.40,   7.60,   7.80,
     8.00,   8.20,   8.40,   8.60,   8.80,
     9.00,   9.20,   9.40,   9.60,   9.80,
    10.00,  10.50,  11.00,  11.50,  12.00,
    12.50,  13.00,  13.50,  14.00,  14.50,
    15.00,  15.50,  16.00,  16.50,  17.00,
    17.50,  18.00,  18.50,  19.00,  19.50,
    20.00,  21.00,  22.00,  23.00,  24.00,
    25.00,  26.00,  27.00,  28.00,  29.00,
    30.00,  32.00,  34.00,  36.00,  38.00,
    40.00,  42.00,  44.00,  46.00,  48.00,
    50.00,  55.00,  60.00,  65.00,  70.00,
    75.00,  80.00,  85.00,  90.00,  95.00,
  100.00, 110.00, 120.00, 130.00, 140.00,
  150.00, 160.00, 170.00, 180.00, 190.00,
  200.00, 210.00, 220.00, 230.00, 240.00,
  250.00, 260.00, 270.00, 280.00, 290.00,
  300.00, 310.00, 320.00, 330.00, 340.00,
  350.00, 360.00, 370.00, 380.00, 390.00,
  400.00, 410.00, 420.00, 430.00, 440.00,
  450.00, 460.00, 470.00, 480.00, 490.00,
  500.00, 510.00, 520.00, 530.00, 540.00,
  550.00, 560.00, 570.00, 580.00, 590.00,
  600.00, 610.00, 620.00, 630.00, 640.00,
  650.00, 660.00, 670.00, 680.00, 690.00,
  700.00, 710.00, 720.00, 730.00, 740.00,
  750.00, 760.00, 770.00, 780.00, 790.00,
  800.00, 810.00, 820.00, 830.00, 840.00,
  850.00, 860.00, 870.00, 880.00, 890.00,
  900.00, 910.00, 920.00, 930.00, 940.00,
  950.00, 960.00, 970.00, 980.00, 990.00,
  1000.00);



  function Get_Tic_Index(Price : Fixed_Type) return Tics_Type is
   begin
     for I in Global_Odds_Table'Range loop
       if Global_Odds_Table(I) = Price then
         return I;
       end if;
     end loop;
     raise Bad_Odds with Price'Img;
   end Get_Tic_Index;


  procedure Test_Float_To_Fix_Conversion is
     Flt : Float := 1.0;
     Fix1 : Fixed_Type := 0.0;
     Fix2 : Fixed_Type := 0.0;
     Tc1 : Tics_Type:= Tics_Type'First;
     Tc2 : Tics_Type:= Tics_Type'First;
   begin
     loop
       Flt := Flt + 0.001;

       Fix1 := Fixed_Type(Flt);
       Fix2 := Fixed_Type'Round(Flt);

       begin
         Tc1 := Get_Tic_Index(Fix1);
         Log("Test_Float_To_Fix_Conversion", "1 " &  Fix1'Img &  " -> " 
& Tc1'Img);
       exception
         when Bad_Odds =>
           Log("Test_Float_To_Fix_Conversion", "Bad odds 1 " & Fix1'Img);
       end;

       begin
         Tc2 := Get_Tic_Index(Fix2);
         Log("Test_Float_To_Fix_Conversion", "2 " &  Fix2'Img & " -> " & 
Tc2'Img);
       exception
         when Bad_Odds =>
           Log("Test_Float_To_Fix_Conversion", "Bad odds 2 " & Fix2'Img);
       end;
       exit when Flt > 1000.0;
     end loop;

   end Test_Float_To_Fix_Conversion;
   ------------------------------------------

-- 
Björn