83 lines
2.1 KiB
C++
83 lines
2.1 KiB
C++
/* String implementation details, mainly regarding Unicode support.
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*
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* This file is part of libostd. See COPYING.md for futher information.
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*/
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#include <cstdint>
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#include "ostd/string.hh"
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namespace ostd {
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namespace utf {
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constexpr std::uint32_t MaxCodepoint = 0x10FFFF;
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static inline bool codepoint_dec(string_range &r, char32_t &cret) {
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static const std::uint32_t ulim[] = { 0xFF, 0x7F, 0x7FF, 0xFFFF };
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if (r.empty()) {
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return false;
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}
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std::uint32_t ch = static_cast<unsigned char const>(r.front());
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if (ch <= 0x7F) {
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/* ASCII */
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cret = ch;
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r.pop_front();
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return true;
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}
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std::uint32_t ret = 0;
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string_range sr = r;
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sr.pop_front();
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/* continuation bytes */
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for (; ch & 0x40; ch <<= 1) {
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/* need a continuation byte but nothing left in the string */
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if (sr.empty()) {
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return false;
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}
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/* the continuation byte */
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std::uint32_t nch = static_cast<unsigned char const>(sr.front());
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sr.pop_front();
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/* lower 6 bits */
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std::uint32_t bch = nch & 0x3F;
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/* not a continuation byte */
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if ((nch ^ bch) != 0x80) {
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return false;
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}
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/* the 6 bits go in the result */
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ret = (ret << 6) | bch;
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}
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/* number of continuation bytes */
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std::size_t n = sr.data() - r.data();
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/* invalid sequence - too many continuation bits */
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if (n > 3) {
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return false;
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}
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/* add the up to 7 bits from the first byte, already shifted left by n */
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ret |= (ch & 0x7F) << (n * 5);
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/* invalid sequence - out of bounds */
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if ((ret > MaxCodepoint) || (ret <= ulim[n])) {
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return false;
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}
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cret = ret;
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r = sr;
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return true;
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}
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bool codepoint(string_range &r, char32_t &ret) {
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return codepoint_dec(r, ret);
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}
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std::size_t length(string_range r, string_range &cont) {
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std::size_t ret = 0;
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for (char32_t ch = U'\0'; codepoint_dec(r, ch); ++ret) {
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continue;
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}
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cont = r;
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return ret;
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}
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std::size_t length(string_range r) {
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return length(r, r);
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}
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} /* namespace utf */
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} /* namespace ostd */
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