Integer to string

// Yet another itoa_10 implementation
int int_to_string(const int32_t init_value, char* const buffer) {
    char* pstart = buffer;
    uint32_t value;
    if (init_value < 0) {
        value = -init_value;
        *pstart++ = '-';
    } else {
        value = init_value;
    }

    // INT_MAX = 2147483647
    int bufneed;

    if (value >= uint32_t(1e9)) {
        if (value >= uint32_t(2e9)) {
            *pstart++ = '2';
            value -= uint32_t(2e9);

            if (value >= uint32_t(1e8)) {
                *pstart++ = '1';
                value -= uint32_t(1e8);
            } else {
                *pstart++ = '0';
            }
            bufneed = 8;
        } else {
            *pstart++ = '1';
            bufneed = 9;
        }
    } else {
        // 123456789
        if (value >= uint32_t(1e4)) {
            if (value >= uint32_t(1e6)) {
                if (value >= uint32_t(1e8)) {
                    bufneed = 9;
                } else if (value >= uint32_t(1e7)) {
                    bufneed = 8;
                } else {
                    bufneed = 7;
                }
            } else if (value >= uint32_t(1e5)) {
                bufneed = 6;
            } else {
                bufneed = 5;
            }
        } else if (value >= uint32_t(1e2)) {
            if (value >= uint32_t(1e3)) {
                bufneed = 4;
            } else {
                bufneed = 3;
            }
        } else if (value >= uint32_t(1e1)) {
            bufneed = 2;
        } else {
            pstart[0] = '0' + value;
            pstart[1] = '\0';
            return int(&pstart[1] - buffer);
        }
    }
    char* pend = pstart + bufneed;
    int res = int(pend - buffer);
    *pend-- = '\0';
    while (value > 0) {
        *pend-- = '0' + value % 10;
        value /= 10;
    }
    while (pend >= pstart) {
        *pend-- = '0';
    }
    return res;
}