AuroraRuntime/Source/Locale/Encoding/UTFn/AuUTF32.hpp

/***
    Copyright (C) 2021 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuUTF32.hpp
    Date: 2021-10-31
    Author: Reece
***/
#pragma once

namespace Aurora::Locale::Encoding::UTF32
{
    static void SwapU32(void *base, AuUInt32 count)
    {
        count *= 4;
        for (int i = 0; i < count; i += 4)
        {
            AuWriteU32BE(base, i, AuReadU32LE(base, i));
        }
    }
    
    static AuUInt32 Count32(const void *base, AuUInt32 length, bool bytes = false)
    {
        return bytes ? length & ~3 : (length & ~3) / 4;
    }

    static bool WriteCp(AuUInt32 cp, char *& result, AuUInt32 &counter, AuUInt32 max)
    {
        if (cp < 0x80)
        {
            if (counter + 1 > max)
            {
                return false;
            }
            counter += 1;
            *(result++) = static_cast<AuUInt8>(cp);
        }
        else if (cp < 0x800)
        {
            if (counter + 2 > max)
            {
                return false;
            }
            counter += 2;
            *(result++) = static_cast<AuUInt8>((cp >> 6) | 0xc0);
            *(result++) = static_cast<AuUInt8>((cp & 0x3f) | 0x80);
        }
        else if (cp < 0x10000)
        {
            if (counter + 3 > max)
            {
                return false;
            }
            counter += 3;
            *(result++) = static_cast<AuUInt8>((cp >> 12) | 0xe0);
            *(result++) = static_cast<AuUInt8>(((cp >> 6) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>((cp & 0x3f) | 0x80);
        }
        else if (cp < 200000)
        {
            if (counter + 4 > max)
            {
                return false;
            }
            counter += 4;
            *(result++) = static_cast<AuUInt8>((cp >> 18) | 0xf0);
            *(result++) = static_cast<AuUInt8>(((cp >> 12) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 6) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>((cp & 0x3f) | 0x80);
        }
        else if (cp < 400000)
        {
            if (counter + 5 > max)
            {
                return false;
            }
            counter += 5;
            *(result++) = static_cast<AuUInt8>((cp >> 24) | 0xf8);
            *(result++) = static_cast<AuUInt8>(((cp >> 18) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 12) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 6) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>((cp & 0x3f) | 0x80);
        }
        else if (cp < 80000000)
        {
            if (counter + 6 > max)
            {
                return false;
            }
            counter += 6;
            *(result++) = static_cast<AuUInt8>((cp >> 30) | 0xfc);
            *(result++) = static_cast<AuUInt8>(((cp >> 24) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 18) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 12) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>(((cp >> 6) & 0x3f) | 0x80);
            *(result++) = static_cast<AuUInt8>((cp & 0x3f) | 0x80);
        }
        else
        {
            return false;
        }
        return true;
    }
    
    static bool ReadUtf8ByteString(AuUInt32 *cp, AuUInt32 *&cpEnd, const char *&s, const char *end)
    {
        if (!s)
        {
            return false;
        }

        if (!cp)
        {
            cpEnd = cp;
        }

        auto &it = s;
    
        while ((it < end) && // can coomsome
               (cp && cp < cpEnd))
        {
            AuUInt32 c = 0;
            if (*it <= 0x7FU)
            {
                c = *it;
                ++it;
            }
            else
            {
                if ((*it & 0xC0U) != 0xC0U)
                {
                    return false;
                }

                AuUInt32 nby = 0;
                for (AuUInt8 b = *it; (b & 0x80U) != 0; b <<= 1, ++nby)
                {}

                if (nby > 6)
                {
                    return false;
                }

                if ((end - it) < nby)
                {
                    return false;
                }

                c = *it & (AuUInt8(0xFFU) >> (nby + 1));

                for (AuUInt32 i = 1; i < nby; ++i)
                {
                    if ((it[i] & 0xC0U) != 0x80U)
                    {
                        return false;
                    }

                    c = (c << 6) | (it[i] & 0x3FU);
                }

                it += nby;
            }

            if (cp)
            {
                *cp = c;
                cp++;
            }

            cpEnd++;
        }
    }
    
    static AuUInt32 CountU8Overhead(AuUInt32 cp)
    {
        if (cp < 0x80)
            return 1;
        else if (cp < 0x800)
            return 2;
        else if (cp < 0x10000)
            return 3;
        else if (cp < 200000)
            return 4;
        else if (cp < 400000)
            return 5;
        else if (cp < 80000000)
            return 6;
    }
}