...

1 files changed, 100 insertions, 0 deletions

diff --git a/src/win/string.cpp b/src/win/string.cpp
index 84906f6b..c8b0ca87 100644
--- a/src/win/string.cpp
+++ b/src/win/string.cpp
@@ -2,6 +2,8 @@
 
 #include "cru/win/exception.hpp"
 
+#include <type_traits>
+
 namespace cru::platform::win {
 std::string ToUtf8String(const std::wstring_view& string) {
   if (string.empty()) return std::string{};
@@ -43,4 +45,102 @@ std::wstring ToUtf16String(const std::string_view& string) {
                           "Failed to convert wide string to UTF-16.");
   return result;
 }
+
+template <typename UInt, int number_of_bit>
+inline std::enable_if_t<std::is_unsigned_v<UInt>, CodePoint> ExtractBits(
+    UInt n) {
+  return static_cast<CodePoint>(n & ((1u << number_of_bit) - 1));
+}
+
+CodePoint Utf8Iterator::Next() {
+  if (position_ == static_cast<int>(string_.length())) return k_code_point_end;
+
+  const auto cu0 = static_cast<std::uint8_t>(string_[position_++]);
+
+  auto read_next_folowing_code = [this]() -> CodePoint {
+    if (this->position_ == static_cast<int>(string_.length()))
+      throw TextEncodeException(
+          "Unexpected end when read continuing byte of multi-byte code point.");
+
+#ifdef CRU_DEBUG
+    const auto u = static_cast<std::uint8_t>(string_[position_]);
+    if (!(u & (1u << 7)) || (u & (1u << 6))) {
+      throw TextEncodeException(
+          "Unexpected bad-format (not 0b10xxxxxx) continuing byte of "
+          "multi-byte code point.");
+    }
+#endif
+
+    return ExtractBits<std::uint8_t, 6>(string_[position_++]);
+  };
+
+  if ((1u << 7) & cu0) {
+    if ((1u << 6) & cu0) {      // 2~4-length code point
+      if ((1u << 5) & cu0) {    // 3~4-length code point
+        if ((1u << 4) & cu0) {  // 4-length code point
+#ifdef CRU_DEBUG
+          if (cu0 & (1u << 3)) {
+            throw TextEncodeException(
+                "Unexpected bad-format begin byte (not 0b10xxxxxx) of 4-byte "
+                "code point.");
+          }
+#endif
+
+          const CodePoint s0 = ExtractBits<std::uint8_t, 3>(cu0) << (6 * 3);
+          const CodePoint s1 = read_next_folowing_code() << (6 * 2);
+          const CodePoint s2 = read_next_folowing_code() << 6;
+          const CodePoint s3 = read_next_folowing_code();
+          return s0 + s1 + s2 + s3;
+        } else {  // 3-length code point
+          const CodePoint s0 = ExtractBits<std::uint8_t, 4>(cu0) << (6 * 2);
+          const CodePoint s1 = read_next_folowing_code() << 6;
+          const CodePoint s2 = read_next_folowing_code();
+          return s0 + s1 + s2;
+        }
+      } else {  // 2-length code point
+        const CodePoint s0 = ExtractBits<std::uint8_t, 5>(cu0) << 6;
+        const CodePoint s1 = read_next_folowing_code();
+        return s0 + s1;
+      }
+    } else {
+      throw TextEncodeException(
+          "Unexpected bad-format (0b10xxxxxx) begin byte of a code point.");
+    }
+  } else {
+    return static_cast<CodePoint>(cu0);
+  }
+}
+
+CodePoint Utf16Iterator::Next() {
+  if (position_ == static_cast<int>(string_.length())) return k_code_point_end;
+
+  const auto cu0 = static_cast<std::uint16_t>(string_[position_++]);
+
+  if (cu0 < 0xd800u || cu0 >= 0xe000u) {  // 1-length code point
+    return static_cast<CodePoint>(cu0);
+  } else if (cu0 <= 0xdbffu) {  // 2-length code point
+    if (position_ == static_cast<int>(string_.length())) {
+      throw TextEncodeException(
+          "Unexpected end when reading second code unit of surrogate pair.");
+    }
+    const auto cu1 = static_cast<std::uint16_t>(string_[position_++]);
+
+#ifdef CRU_DEBUG
+    if (cu1 < 0xDC00u || cu1 > 0xdfffu) {
+      throw TextEncodeException(
+          "Unexpected bad-format second code unit of surrogate pair.");
+    }
+#endif
+
+    const auto s0 = ExtractBits<std::uint16_t, 10>(cu0) << 10;
+    const auto s1 = ExtractBits<std::uint16_t, 10>(cu1);
+
+    return s0 + s1 + 0x10000;
+
+  } else {
+    throw TextEncodeException(
+        "Unexpected bad-format first code unit of surrogate pair.");
+  }
+}
+
 }  // namespace cru::platform::win