Re: Translating an embedded C algorithm

["Steve" <nospam_steved94@comcast.net>]

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"Talulah" <paul.hills@uk.landisgyr.com> wrote in message 
news:1168871816.263502.212100@11g2000cwr.googlegroups.com...
> Hi,
>
> I am in the process of writing a book about real-time embedded
> development (hardware and software). In it there is a section on
> different programming languages that are available for embedded
> development. I'm using a small C function that does temperature
> measurement by linear interpolation of a lookup table as an example. I
> have C code to do this, and would like to have the same algorithm
> implemented in other languages.
>
> Unfortunately I'm really a C programmer, with very little experience
> of other languages, so I would like to ask if anyone on this newsgroup
> is interested in translating the algorithm into Ada. Of course you
> would be mentioned in thanks in the book once it is finished.
>

Here is a bit more Ada-ish version:

with Interfaces;
package Temperature_Evaluation is

    type Kelvin_Tenths is new Interfaces.Integer_16;

    type Adc_Reading is range 0 .. 2**10-1;

  ------------------------------------------------------------------------
  -- MeasureTemperature
  --
  -- Calculates the temperature in �C given the ADC count by lookup
  -- table and linear interpolation of the diode circuit characteristic.
  --
  -- Parameters:
  -- AdcCount Raw ADC count.
  --
  -- Returns:
  -- Temperature in �C x 10. INVALID_TEMPERATURE if out of range.
  ------------------------------------------------------------------------
    function MeasureTemperature( AdcCount : Adc_Reading ) return 
Kelvin_Tenths;

end Temperature_Evaluation;

with Interfaces;

package body Temperature_Evaluation is

    ----------------------------------------------------------------------
    -- The Temperature_Lookup table is used to map ADC counts to a
    -- temperature in kelvins.
    -- Consecutive values in the table represent an increase of 8 ADC
    -- counts.
    -- The ADC value of the first entry in the table is given by:
    -- Base_Adc_Value;
    ----------------------------------------------------------------------
    Interp_Interval    : constant := 8;
    Base_Adc_Value     : constant := 220;
    Temperature_Lookup : constant array( Positive range <>) of Kelvin_Tenths 
:=
    (
        1171, 1116, 1061, 1006,  952,  899,  846, 793,
         741,  689,  638,  588,  537,  488,  438, 389,
         341,  293,  246,  199,  152,  106,   61,  16,
         -29,  -73, -116, -160, -202, -244, -286, -327
    );

------------------------------------------------------------------------
-- MeasureTemperature
--
-- Calculates the temperature in �C given the ADC count by lookup
-- table and linear interpolation of the diode circuit characteristic.
--
-- Parameters:
-- AdcCount Raw ADC count.
--
-- Returns:
-- Temperature in �C x 10. INVALID_TEMPERATURE if out of range.
------------------------------------------------------------------------
function MeasureTemperature( AdcCount : Adc_Reading ) return Kelvin_Tenths 
is

    Table_Index     : Integer;
    Table_Remainder : Integer;
    Temperature     : Kelvin_Tenths;
    Temp_Diff       : Integer;

begin
    --------------------------------------------------------------------
    -- Evaluate the index into Temperature_Lookup as well as remaining
    -- Adc counts that are not covered by the lookup.
    --------------------------------------------------------------------
    Table_Index     :=   Temperature_Lookup'First
                       + (Integer(AdcCount) - Base_Adc_Value) / 
Interp_Interval;

    Table_Remainder := (Integer(AdcCount) - Base_Adc_Value) rem 
Interp_Interval;

    --------------------------------------------------------------------
    -- Check the index against the bounds of the lookup table
    --------------------------------------------------------------------

    if Table_Index < Temperature_Lookup'First then
        ----------------------------------------------------------------
        -- For an index before the first index of the table, use
        -- the first index.
        ----------------------------------------------------------------
        Table_Index := Temperature_Lookup'First;
    elsif Table_Index >= Temperature_Lookup'Last then
        ----------------------------------------------------------------
        -- For an index that at or beyond the last index of the table,
        -- use the last index.
        ----------------------------------------------------------------
        Table_Index := Temperature_Lookup'Last;
    end if;

    --------------------------------------------------------------------
    -- Evaluate the base temperature value
    --------------------------------------------------------------------
    Temperature := Temperature_Lookup( Table_Index );

    if Table_Remainder /= 0 then
        Temp_Diff   := Integer(Temperature_Lookup( Table_Index + 1 ) - 
Temperature_Lookup( Table_Index ));
        Temperature :=   Temperature
                       + Kelvin_Tenths( ( Temp_Diff * Table_Remainder ) / 
Interp_Interval);
    end if;

    return Temperature + ReadEeprom(TEMPERATURE_CAL_VALUE);
end MeasureTemperature;

end Temperature_Evaluation;

I took the liberty of making minor changes in the logic which I believe 
simplifies things a bit.

Regards,
Steve
(The Duck)

> If you are interested, I have placed the section of the book here:
>
> http://homepages.which.net/~paul.hills/Temporary/Temperature.pdf
>
> so you can see the code and description. Please email me if you are
> interested to paul (dot) hills (who is at) uk (dot) landisgyr (dot)
> com.
>
> Thanks very much
> Paul Hills
>