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Added approximation for POSIX expm1() function for MSVC compilers

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This commit is contained in:
Dee Holtsclaw 2012-08-23 09:41:31 -04:00
parent 7e0d3396b7
commit de05d2b60c
1 changed files with 25 additions and 1 deletions
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26
src/core/qxtcurrency.cpp
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@ -320,6 +320,30 @@ QxtCurrency QxtCurrency::clamped(const QxtCurrency &low,
return *this;
}
/* Ugly hack for crippled MSVC versions missing the expm1() POSIX function.
*
* The alternative implementation was obtained from John Cook.
*
* http://www.johndcook.com/cpp_expm1.html
*
* NOTE: MSDN indicates the "expm1()" function is available in MSVC 2012
* and later editions. It's not clear, however, if this includes the
* "Express" editions so further testing is advised.
*/
#if defined(_MSC_VER)
inline double qxt_expm1(double n)
{
if(fabs(n) < 1e-5)
// Small value, use 2-term Taylor series approximation
return n + 0.5*n*n;
else
// Large value, use native exp() function and subtract 1.0
return exp(n) - 1.0;
}
#else
inline double qxt_expm1(double n) { return expm1(n); }
#endif
/*! Calculates the proper payment amount for an amortized loan repayment
* schedule. Given a principal amount \a P (that being borrowed), a periodic
* interest rate \a r and \a n payments, the result is the minimum payment
@ -343,7 +367,7 @@ QxtCurrency QxtCurrency::amortizedPayment(const QxtCurrency &P, double r, int n)
if(n > 1){
if(r >= 0.000001){
double nval = double(n)*log(1.0+r);
pmt = QxtCurrency(r * double(P) * exp(nval) / expm1(nval));
pmt = QxtCurrency(r * double(P) * exp(nval) / qxt_expm1(nval));
}
else
pmt = P / n;