[libc-commits] [libc] [libc] utf8 to 32 CharacterConverter (PR #143973)

[Uzair Nawaz via libc-commits]

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@@ -22,13 +23,68 @@ bool CharacterConverter::isComplete() {
   return state->bytes_processed == state->total_bytes;
 }
 
-int CharacterConverter::push(char8_t utf8_byte) {}
-
-int CharacterConverter::push(char32_t utf32) {}
-
-utf_ret<char8_t> CharacterConverter::pop_utf8() {}
+int CharacterConverter::push(char8_t utf8_byte) {
+  // Checking the first byte if first push
+  if (state->bytes_processed == 0 && state->total_bytes == 0) {
+    state->partial = static_cast<char32_t>(0);
+    // 1 byte total
+    if (cpp::countl_one(utf8_byte) == 0) {
+      state->total_bytes = 1;
+    }
+    // 2 bytes total
+    else if (cpp::countl_one(utf8_byte) == 2) {
+      state->total_bytes = 2;
+      utf8_byte &= 0x1F;
+    }
+    // 3 bytes total
+    else if (cpp::countl_one(utf8_byte) == 3) {
+      state->total_bytes = 3;
+      utf8_byte &= 0x0F;
+    }
+    // 4 bytes total
+    else if (cpp::countl_one(utf8_byte) == 4) {
+      state->total_bytes = 4;
+      utf8_byte &= 0x07;
+    }
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uzairnawaz wrote:

Might be slightly better to store the result of `count1_one` in a variable instead of making repeated calls.

https://github.com/llvm/llvm-project/pull/143973