src/text/utf.cpp

#include "rive/text/utf.hpp"
#include "rive/core/type_conversions.hpp"

using namespace rive;

static constexpr Unichar kReplacementCharacter = 0xFFFD;

int UTF::CountUTF8Length(const uint8_t utf8[])
{
  unsigned lead = *utf8;
  assert(lead != 0xFF);
  assert((lead & 0xC0) != 0x80); // 10xxxxxx is not a legal lead byte
  if ((lead & 0x80) == 0)
  {
    return 1;
  }
  int n = 1;
  lead <<= 1;
  while (lead & 0x80)
  {
    n += 1;
    lead <<= 1;
  }
  assert(n >= 1 && n <= 4);
  return n;
}

Unichar UTF::NextUTF8(const uint8_t** utf8Ptr, const uint8_t* end)
{
  const uint8_t* text = *utf8Ptr;
  uint32_t c = *text++;
  if (c >= 0x80)
  {
    // A stray continuation byte or a lead past 0xF7 starts no sequence.
    int more = c >= 0xF8   ? -1
               : c >= 0xF0 ? 3
               : c >= 0xE0 ? 2
               : c >= 0xC0 ? 1
                           : -1;
    c = more < 0 ? kReplacementCharacter : c & (0x3F >> more);
    for (; more > 0; more--)
    {
      // Guest text can end mid sequence, and the byte after it starts
      // the next one.
      if (text == end || (*text & 0xC0) != 0x80)
      {
        c = kReplacementCharacter;
        break;
      }
      c = (c << 6) | (*text++ & 0x3F);
    }
  }
  *utf8Ptr = text;
  return c;
}

int UTF::ToUTF16(Unichar uni, uint16_t utf16[])
{
  if (uni > 0xFFFF)
  {
    utf16[0] = castTo<uint16_t>(0xD800 + ((uni - 0x10000) >> 10));
    utf16[1] = castTo<uint16_t>(0xDC00 | (uni & 0x3FF));
    return 2;
  }
  utf16[0] = castTo<uint16_t>(uni);
  return 1;
}

uint32_t UTF::CountCodePointLength(Span<const Unichar> codepoints)
{
  uint32_t length = 0;
  for (auto codepoint : codepoints)
  {
    if (codepoint <= 0x7F)
    {
      length += 1;
    }
    else if (codepoint <= 0x07FF)
    {
      length += 2;
    }
    else if (codepoint <= 0xFFFF)
    {
      length += 3;
    }
    else if (codepoint <= 0x10FFFF)
    {
      length += 4;
    }
  }
  return length;
}

uint32_t UTF::Encode(uint8_t* output, Unichar codepoint)
{
  if (codepoint <= 0x7F)
  {
    output[0] = (uint8_t)codepoint;
    return 1;
  }
  else if (codepoint <= 0x07FF)
  {
    output[0] = (uint8_t)(((codepoint >> 6) & 0x1F) | 0xC0);
    output[1] = (uint8_t)(((codepoint >> 0) & 0x3F) | 0x80);
    return 2;
  }
  else if (codepoint <= 0xFFFF)
  {
    output[0] = (uint8_t)(((codepoint >> 12) & 0x0F) | 0xE0);
    output[1] = (uint8_t)(((codepoint >> 6) & 0x3F) | 0x80);
    output[2] = (uint8_t)(((codepoint >> 0) & 0x3F) | 0x80);
    return 3;
  }
  else if (codepoint <= 0x10FFFF)
  {
    output[0] = (uint8_t)(((codepoint >> 18) & 0x07) | 0xF0);
    output[1] = (uint8_t)(((codepoint >> 12) & 0x3F) | 0x80);
    output[2] = (uint8_t)(((codepoint >> 6) & 0x3F) | 0x80);
    output[3] = (uint8_t)(((codepoint >> 0) & 0x3F) | 0x80);
    return 4;
  }
  else
  {
    // error
    return 0;
  }
}