merge_skill.c

/**
  * `n` persons with skill `sn` are merged into `add` persons with skill `sv`
  */
int merge_skill(const skill* sv, const skill* sn, skill* result, int n, int add)
{
    int total = add + n;
    /* number of person-weeks the units have already studied: */
    int days, weeks = weeks_from_level(sn ? sn->level : 0) * n
        + weeks_from_level(sv ? sv->level : 0) * add;
    /* level that combined unit should be at: */
    int level = level_from_weeks(weeks, total);

    /* minimum new level, based only on weeks spent towards current levels: */
    result->level = level;
    /* average time to the next level: */
    result->days = (level + 1) * SKILL_DAYS_PER_WEEK;

    /* add any remaining weeks to the already studied ones and convert to days: */
    weeks -= weeks_from_level(level) * total;
    days = weeks * SKILL_DAYS_PER_WEEK;

    /* adjusted by how much we already studied: */
    if (sv) days += days_studied(sv) * add;
    if (sn) days += days_studied(sn) * n;
    if (days < 0) {
        result->days -= days / total;
    }
    else if (days >= total) {
        days = result->days - days / total;
        while (days < 0) {
            ++result->level;
            days += result->level * SKILL_DAYS_PER_WEEK;
        }
        result->days = days;
    }
    return result->level;
}

merge_skill_2.c

/**
  * `n` persons with skill `sn` are merged into `add` persons with skill `sv`
  */
int merge_skill(const skill* sv, const skill* sn, skill* result, int n, int add)
{
    int total = add + n;
    /* number of person-weeks the units have already studied: */
    int days, weeks = weeks_from_level(sn ? sn->level : 0) * n
        + weeks_from_level(sv ? sv->level : 0) * add;
    /* level that combined unit should be at: */
    int level = level_from_weeks(weeks, total);

    /* minimum new level, based only on weeks spent towards current levels: */
    result->level = level;
    /* average time to the next level: */
    result->days = (level + 1) * SKILL_DAYS_PER_WEEK;

    /* add any remaining weeks to the already studied ones and convert to days: */
    weeks -= weeks_from_level(level) * total;
    days = weeks * SKILL_DAYS_PER_WEEK;

    /* adjusted by how much we already studied: */
    if (sv) days += days_studied(sv) * add;
    if (sn) days += days_studied(sn) * n;
    if (days < 0) {
        result->days -= days / total;
    }
    else if (days >= total) {
        int pdays = total * result->days - days;
        while (pdays < 0) {
            ++result->level;
            pdays += total * result->level * SKILL_DAYS_PER_WEEK;
        }
        result->days = (pdays + total - 1 ) / total;
    }
    return result->level;
}