ftoa, dtoa, ulltoa

void
__CRT_ulltoa(uint64_t val, /*not const*/ char* buf, size_t bufSz, int mode)
{
    if (val)
    {
        uint64_t val2 = val;

        switch (mode)
        {
        case 0:
        case 3:
        default:
        {
            if (mode == 3)
                val2 = __CRT_dectooctll(val);
            int bufferIndex = 0;
            while (1)
            {
                unsigned long long mod = val2 % 10;
                __CRT_itoa_internalBuffer[bufferIndex++] = (char)mod;

                val2 = val2 / 10;

                if (!val2)
                    break;
            }
            if (bufferIndex)
            {
                int dstBufInd = 0;
                for (int i = 0; i < bufferIndex; ++i)
                {
                    buf[dstBufInd++] = __CRT_itoa_internalBuffer[bufferIndex - i - 1] + '0';
                    if (dstBufInd == bufSz)
                        break;
                }
                buf[dstBufInd] = 0;
            }
        }
        break;
        case 1:
        case 2:
        {
            int bsz = 0;
            char hexbuf[10];
            __CRT_dectohex(val, hexbuf, &bsz);
            if (bsz)
            {
                for (int i = 0; i < bsz; ++i)
                {
                    buf[i] = hexbuf[i];
                    buf[i + 1] = 0;
                }
            }
            if (mode == 2)
            {
                for (size_t i2 = 0; i2 < bufSz; ++i2)
                {
                    if (islower(buf[i2]))
                        buf[i2] = toupper(buf[i2]);

                    if (!buf[i2])
                        break;
                }
            }
        }break;
        }
    }
    else
    {
        buf[0] = '0';
        buf[1] = 0;
    }
}

char __CRT_itoa_buffer[31]; // for vsnprintf

// `buf` is a __CRT_dtoa_buffer if it called by __CRT_vsnprintf
// I can use __CRT_itoa_buffer here for i1 and i2
void
_C_DECL
__CRT_dtoa(double val, char* buf, size_t bufSz, int mode)
{
    int isMinus = 0;
    if (val < 0.0)
        isMinus = 1;

    int bufInd = 0;

    if (isMinus)
    {
        buf[bufInd++] = '-';
        buf[bufInd] = 0;
    }

    double ipart = 0.0;
    double in = modf(val, &ipart);
    in *= 10000000000000000;

    uint64_t i1 = (uint64_t)ipart;
    uint64_t i2 = (uint64_t)in;

    __CRT_ulltoa(i1, __CRT_itoa_buffer, 30, 0);
    if (__CRT_itoa_buffer[0])
    {
        for(int i = 0; i < 30; ++i)
        {
            if (!__CRT_itoa_buffer[i])
                break;

            buf[bufInd++] = __CRT_itoa_buffer[i];
            buf[bufInd] = 0;

            if (bufInd == bufSz)
                return;
        }
    }

    struct lconv* loc = localeconv();

    buf[bufInd++] = loc->decimal_point[0];
    buf[bufInd] = 0;

    if (bufInd == bufSz)
        return;

    __CRT_ulltoa(i2, __CRT_itoa_buffer, 30, 0);
    if (__CRT_itoa_buffer[0])
    {
        for (int i = 0; i < 30; ++i)
        {
            if (!__CRT_itoa_buffer[i])
                break;

            buf[bufInd++] = __CRT_itoa_buffer[i];
            buf[bufInd] = 0;

            if (bufInd == bufSz)
                return;
        }
    }
    buf[bufInd] = 0;
}


void
__CRT_ftoa(float val, char* buf, size_t bufSz, int mode)
{
    __CRT_dtoa(val, buf, bufSz, mode);
}