[libc-commits] [libc] [libc] Implemented CharacterConverter push/pop for utf32->utf8 conversions (PR #143971)

[Brooks Moses via libc-commits]

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@@ -22,13 +24,61 @@ bool CharacterConverter::isComplete() {
   return state->bytes_processed == state->total_bytes;
 }
 
-int CharacterConverter::push(char8_t utf8_byte) {}
+int CharacterConverter::push(char32_t utf32) {
+  state->partial = utf32;
+  state->bytes_processed = 0;
+  state->total_bytes = 0;
 
-int CharacterConverter::push(char32_t utf32) {}
+  // determine number of utf-8 bytes needed to represent this utf32 value
+  constexpr char32_t ranges[] = {0x7f, 0x7ff, 0xffff, 0x10ffff};
+  constexpr int num_ranges = 4;
+  for (uint8_t i = 0; i < num_ranges; i++) {
+    if (state->partial <= ranges[i]) {
+      state->total_bytes = i + 1;
+      break;
+    }
+  }
+  if (state->total_bytes == 0)
+    return -1;
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brooksmoses wrote:

It would be good to add a comment here explaining that the error case is when the input value is too large to be represented in four bytes of UTF-8.

https://github.com/llvm/llvm-project/pull/143971