Black-Scholes in Delphi [closed]

when trying to implement the Black-Scholes formula in Delphi, I've found this: http://www.espenhaug.com/black_scholes.html

I've checked the results against option-price.com and found they are different. Can anyone share the code for the B&S formula in Delphi/FreePascal (from a different source than espenhaug.com?.

{Black and Scholes (1973) Stock options}

function BlackScholes(CallPutFlag : string; S, X, T, r, v : Double): Double;
var
d1, d2 : Double;

begin
Result := 0;
d1 := (LN(S / X) + (r + Power(v, 2) / 2) * T) / (v * SqRt(T));
d2 := d1 - v * SqRt(T);
if CallPutFlag = 'c' then
Result := S * CND(d1) - X * Exp(-r * T) * CND(d2)
else
if CallPutFlag = 'p' then
Result := X * Exp(-r * T) * CND(-d2) - S * CND(-d1);
end;

{The cumulative normal distribution function}
function CND(X : Double) : Double;
var
L, K : Double;

const
a1 = 0.31938153;   a2 = -0.356563782;  a3 = 1.781477937;
a4 = -1.821255978; a5 = 1.330274429;

begin
L := Abs(X);
K := 1 / (1 + 0.2316419 * L);
Result := 1 - 1 / SqRt(2 * Pi) * Exp(-Power(L, 2) / 2)
* (a1 * K + a2 * Power(K, 2) + a3 * Power(K, 3)
+ a4 * Power(K, 4) + a5 * Power(K, 5));
if X < 0 then
Result := (1 - Result)
end;

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closed as off-topic by Joshua Ulrich, Andrew Cheong, olaker♦Aug 7 '13 at 6:08

• This question does not appear to be about quantitative finance within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

BS is BS is BS, regardless of implementation language used. I venture to say, given you have double checked the formulae that you probably calculate the cdf incorrectly. – Matt Wolf Aug 4 '13 at 5:13
@MattWolf, sorry, what's the "cdf"?. – leonardorame Aug 4 '13 at 13:29
@MattWolf, thanks. I've replaced my CND function by this one: johndcook.com/cpp_phi.html, but the result is the same. – leonardorame Aug 4 '13 at 13:56
@MattWolf, sorry, the BS value is correct now. What I'm getting wrong is the Implied Volatility. I'll open a new question asking for it. – leonardorame Aug 4 '13 at 14:09
This question appears to be off-topic because it is too localized, since the issue was an incorrect function input. – Joshua Ulrich Aug 6 '13 at 21:28