utf_32.hpp

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// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "char_converter.hpp"
 
namespace hi { inline namespace v1 {
 
template<>
struct char_map<"utf-32"> {
    using char_type = char32_t;
 
    [[nodiscard]] std::endian guess_endian(void const *ptr, size_t size, std::endian endian) const noexcept
    {
        hi_assert_not_null(ptr);
        auto *ptr_ = reinterpret_cast<uint8_t const *>(ptr);
 
        if (size < 4) {
            return std::endian::native;
        } else {
            // Check for BOM.
            if (ptr_[0] == 0x00 and ptr_[1] == 0x00 and ptr_[2] == 0xfe and ptr_[3] == 0xff) {
                return std::endian::big;
            } else if (ptr_[0] == 0xff and ptr_[1] == 0xfe and ptr_[2] == 0x00 and ptr_[3] == 0x00) {
                return std::endian::little;
            }
 
            // Check for sequences of zeros.
            auto count = std::array<size_t, 4>{};
            for (auto i = 0; i != size; ++i) {
                count[i % 4] = ptr_[i] == 0 ? count[i % 4] + 1 : 0;
 
                if (i % 4 == 0 and count[0] >= 8) {
                    return std::endian::big;
                } else if (i % 4 == 3 and count[3] >= 8) {
                    return std::endian::little;
                }
            }
 
            return endian;
        }
    }
 
    template<typename It, typename EndIt>
    [[nodiscard]] constexpr std::pair<char32_t, bool> read(It& it, EndIt last) const noexcept
    {
        hi_axiom(it != last);
 
        if (auto cu = *it++; cu < 0xd800) {
            return {cu, true};
 
        } else if (cu < 0xe000) {
            // Surrogates
            return {0xfffd, false};
 
        } else if (cu < 0x11'0000) {
            return {cu, true};
 
        } else {
            // Out-of-range
            return {0xfffd, false};
        }
    }
 
    [[nodiscard]] constexpr std::pair<uint8_t, bool> size(char32_t code_point) const noexcept
    {
        hi_axiom(code_point < 0x11'0000);
        hi_axiom(not(code_point >= 0xd800 and code_point < 0xe000));
        return {uint8_t{1}, true};
    }
 
    template<typename It>
    constexpr void write(char32_t code_point, It& dst) const noexcept
    {
        hi_axiom(code_point < 0x11'0000);
        hi_axiom(not(code_point >= 0xd800 and code_point < 0xe000));
 
        *dst++ = code_point;
    }
 
#if defined(HI_HAS_SSE2)
    template<typename It>
    hi_force_inline __m128i read_ascii_chunk16(It it) const noexcept
    {
        // Load the UTF-16 data.
        hilet c0 = _mm_loadu_si128(reinterpret_cast<__m128i const *>(std::addressof(*it)));
        it += 4;
        hilet c1 = _mm_loadu_si128(reinterpret_cast<__m128i const *>(std::addressof(*it)));
        it += 4;
        hilet c2 = _mm_loadu_si128(reinterpret_cast<__m128i const *>(std::addressof(*it)));
        it += 4;
        hilet c3 = _mm_loadu_si128(reinterpret_cast<__m128i const *>(std::addressof(*it)));
 
        hilet lo = _mm_packs_epi32(c0, c1);
        hilet hi = _mm_packs_epi32(c2, c3);
 
        // To get _mm_packus_epi16() to work we need to prepare the data as follows:
        //  - bit 15 must be '0'.
        //  - if bit 15 was originally set than we need to set any of bits [14:8].
 
        // Positive numbers -> 0b0000'0000
        // Negative numbers -> 0b1000'0000
        hilet sign_lo = _mm_srai_epi16(lo, 15);
        hilet sign_hi = _mm_srai_epi16(hi, 15);
        hilet sign = _mm_packs_epi16(sign_lo, sign_hi);
 
        // ASCII            -> 0b0ccc'cccc
        // positive numbers -> 0b1???'????
        // negative numbers -> 0b0000'0000
        hilet chunk = _mm_packus_epi16(lo, hi);
 
        // ASCII            -> 0b0ccc'cccc
        // positive numbers -> 0b1???'????
        // negative numbers -> 0b1000'0000
        return _mm_or_si128(chunk, sign);
    }
 
    template<typename It>
    hi_force_inline void write_ascii_chunk16(__m128i chunk, It dst) const noexcept
    {
        hilet zero = _mm_setzero_si128();
        hilet lo = _mm_unpacklo_epi8(chunk, zero);
        hilet hi = _mm_unpackhi_epi8(chunk, zero);
 
        hilet c0 = _mm_unpacklo_epi8(lo, zero);
        hilet c1 = _mm_unpackhi_epi8(lo, zero);
        hilet c2 = _mm_unpacklo_epi8(hi, zero);
        hilet c3 = _mm_unpackhi_epi8(hi, zero);
 
        _mm_storeu_si128(reinterpret_cast<__m128i *>(std::addressof(*dst)), c0);
        dst += 4;
        _mm_storeu_si128(reinterpret_cast<__m128i *>(std::addressof(*dst)), c1);
        dst += 4;
        _mm_storeu_si128(reinterpret_cast<__m128i *>(std::addressof(*dst)), c2);
        dst += 4;
        _mm_storeu_si128(reinterpret_cast<__m128i *>(std::addressof(*dst)), c3);
    }
#endif
};
 
}} // namespace hi::v1