Decimal floating-point class

We provide a C++ wrapper class for for Mike Cowlishaw’s decNumber C Library. This documentation (currently only in German – an English version will follow) demonstrates how to use it.

If you are interested in purchasing this C++ source code library, please contact  .img@.img.


Some years ago I wrote a simple C++ wrapper class for Mike Cowlishaw’s decNumber C Library. It was a first try, the design is far from perfect, it is incomplete and notations are sometimes inconsistent. But most of its operators work as they should do, and most of Mikes testcases pass successfully. The function DecimalFloat_Testcases(„d:\\\\decnumber\\decnumberclass\\decTest\\“) in my test program test_rk reads all the testcases from Mikes decTest files and logs each testcase in a file (bcb files were created with Borland C++Builder 6, gcc with MinGW g++, and msc with MS Visual Studio .Net 2003). With “grep „###number“ *.log” you get the summary lines:

File abs.decTest_bcb.log:    ###number of tests passed=87  failed=2
File abs.decTest_gcc.log:    ###number of tests passed=87  failed=2
File abs.decTest_msc.log:    ###number of tests passed=87  failed=2
File add.decTest_bcb.log:    ###number of tests passed=773 failed=45
File add.decTest_gcc.log:    ###number of tests passed=773 failed=46
File add.decTest_msc.log:    ###number of tests passed=773 failed=45

Example usage (more detailled here):

int main(int argc, char* argv[])
cout<<“Test decimal floats:”<<endl;
// decimal float class is DecFloat, defined in “DecFloat.h”
// DecFloats can be initialized with strings, ints and decimal float expressions:
DecFloat d1=”0.70?,
d3=d1*d2;// stream output for DecFloat expressions:
cout<<“d1*d2=”<<d1*d2<<endl;// arithmetic expressions can be formed in the usual way:
int i1=17, i2=123, i3=123;
d1=i1, d2=i2,  d3=i3;
DecFloat x=d1+(d1+d2*d3)-d1*d2;
int      i=i1+(i1+i2*i3)-i1*i2;
cout<<x<<“==”<<i<<endl; // can’t believe it: they are really equal// errors are reported by status flags
// DecContextStatusString() returns them as text
cout<<“After div by 0: DecContextStatusString()=”<<DecContextStatusString()<<endl;
cout<<“After d1=\”abc\”: DecContextStatusString()=”<<DecContextStatusString()<<endl;
cout<<“After ClearStatus(): “<<DecContextStatusString()<<endl;// comparison operators
if (d1<d2)  cout<<“less”<<endl;
if (d1<=d2) cout<<“less equal”<<endl;
if (d1>d2)  cout<<“greater”<<endl;
if (d1>=d2) cout<<“greater equal”<<endl;
if (d1==d2) cout<<“equal”<<endl;
if (d1!=d2) cout<<“not equal”<<endl;// assignments
d1=d2;     // of DecFloats
d1=”1.23?; // of string literals
d1=17;     // of ints{ // filestream output and input
ofstream f(“c:\\dftest.txt”);
}// math epressions pow, max, min, sqrt
cout<<“pow(“<<d1<<“,”<<d2<<“)=”<<pow(d1,d2)<<endl;// pass the directory of the decnumber testcases:
// Most of Mike Cowlishaw’s testcases are processed correctly

return 0;

Download the C++ wrapper class DecFloatClass. To use it, you also have to download the decNumber C Library and pay attention to its licence conditions.


Richard Kaiser
June 10, 2004