Question

Where can I find a free or open source C++ library to do Binary Coded Decimal math?

Answer 1

Here you go. I just wrote this, and am making it public domain.

It converts an unsigned bcd to an unsigned int and vice-versa. Use bcd2i() to convert your BCDs to unsigned ints, do whatever math you need, then use i2bcd() to bring the numbers back to BCD.

unsigned int bcd2i(unsigned int bcd) {
    unsigned int decimalMultiplier = 1;
    unsigned int digit;
    unsigned int i = 0;
    while (bcd > 0) {
        digit = bcd & 0xF;
        i += digit * decimalMultiplier;
        decimalMultiplier *= 10;
        bcd >>= 4;
    }
    return i;
}

unsigned int i2bcd(unsigned int i) {
    unsigned int binaryShift = 0;  
    unsigned int digit;
    unsigned int bcd = 0;
    while (i > 0) {
        digit = i % 10;
        bcd += (digit << binaryShift);
        binaryShift += 4;
        i /= 10;
    }
    return bcd;
}
// Thanks to EmbeddedGuy for bug fix: changed init value to 0 from 1 


#include <iostream>
using namespace std;

int main() {
int tests[] = {81986, 3740, 103141, 27616, 1038, 
               56975, 38083, 26722, 72358, 
                2017, 34259};

int testCount = sizeof(tests)/sizeof(tests[0]);

cout << "Testing bcd2i(i2bcd(test)) on 10 cases" << endl;
for (int testIndex=0; testIndex<testCount; testIndex++) {
    int bcd = i2bcd(tests[testIndex]);
    int i = bcd2i(bcd);
    if (i != tests[testIndex]) {
        cout << "Test failed: " << tests[testIndex] << " >> " << bcd << " >> " << i << endl;
        return 1;
    }
}
cout << "Test passed" << endl;
return 0;
}