Byte array to Signed integer in Delphi -

source array(4 bytes)

[$80,$80,$80,$80] =integer 0 [$80,$80,$80,$81] = 1 [$80,$80,$80,$ff] = 127 [$80,$80,$81,$01] = 128 

need convert integer.

below code , working @ moment.

function convert(b: array of byte): integer; var   i, st, p: integer;   negative: boolean; begin   result := 0;   st := -1;   := 0 high(b)   begin     if b[i] = $80 continue // skip leading 80     else     begin       st := i;       negative := b[i] < $80;       b[i] := abs(b[i] - $80);       break;     end;   end;   if st = -1 exit;   := st high(b)   begin     p := round(power(254, high(b) - i));     result := result + b[i] * p;     result := result - (p div 2);   end;   if negative  result := -1 * result end; 

i'm looking better function?

update:

file link https://drive.google.com/file/d/0byba4qf-yoggzudzcxpmos1aam8/view?usp=sharing

• in uploaded file id field offset 5 9
  

new:
got new problem decoding date field
date field hex [$80,$8f,$21,$c1] -> possible date 1995-12-15
* in uploaded file date field offset 199 203

just example of improvements outlined david.

• the array passed reference const.
• the array fixed in size.
• the use of floating point calculations converted directly constant array.

---

const   maxrange = 3; type   tmyspecial = array[0..maxrange] of byte;  function convert(const b: tmyspecial): integer; var   i, j: integer;   negative: boolean; const   // pwr[i] = round(power(254,maxrange-i));   pwr: array[0..maxrange] of cardinal = (16387064,64516,254,1); begin   := 0 maxrange begin     if (b[i] <> $80) begin       negative := b[i] < $80;       result := abs(b[i] - $80)*pwr[i] - (pwr[i] shr 1);       j := i+1 maxrange         result := result + b[j]*pwr[j] - (pwr[j] shr 1);       if negative         result := -result;       exit;     end;   end;   result := 0; end; 

note less code lines not sign of performance. measure performance before optimizing code in order find real bottlenecks. code readability better optimizing on top.

and future references, please tell algorithm supposed do.

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code testing:

const   x : array[0..3] of tmyspecial =     (($80,$80,$80,$80), // =integer 0      ($80,$80,$80,$81), // = 1      ($80,$80,$80,$ff), // = 127      ($80,$80,$81,$01)); // = 128 var   i,j: integer;   sw: tstopwatch; begin   sw := tstopwatch.startnew;   := 1 100000000     j := 0 3       convert(x[j]);   writeln(sw.elapsedmilliseconds);   readln; end.