Base62 encoding / decoding

base62.cpp

// Base62 encoding / decoding
// Test: `g++ -Wall -g -std=c++11 base4.cpp && ./a.out`

#include <iostream>
#include <algorithm>
#include <time.h>
#include <assert.h>

static const char alphanum[] =
    "0123456789"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz";

long fromBase62(std::string base62) {
    long val = 0;
    long v = 0;
    long multiplier = 1;
    std::reverse(base62.begin(), base62.end());

    for (char& c : base62)
    {
        v = -1;
        for (int i=0; i<62; i++)
        {
            if (c == alphanum[i])
            {
                v = i;
                break;
            }
        }
        assert(v >= 0);
        if (v < 0)
        {
            return 0L;
        }
        val += v * multiplier;
        multiplier *= 62;
    }
    assert(val <= LONG_MAX);
    return val;
}

std::string toBase62(long val)
{
    if (val < 0)
    {
        return "";
    }
    assert(val <= LONG_MAX);
    std::string r;
    r.reserve(11); // for LONG_MAX 9223372036854775807 -> "AzL8n0Y58m7"

    while(val != 0) {
        r += alphanum[(val % 62)];
        val /= 62;
    }
    std::reverse(r.begin(), r.end());
    return r;
}

int main() {
    long timeval = (long)time(NULL);

    std::string b62str = toBase62(timeval);
    std::cout << "Epoch time: " << timeval << "\nTo base62: " << b62str << "\nTo decimal: " << fromBase62(b62str) << std::endl;
}