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node_modules/hermes-parser/dist/HermesParserDecodeUTF8String.js.flow

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+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ * @format
+ */
+
+'use strict';
+
+/**
+ * Decode a UTF-8 encoded string from Hermes with a known length.
+ * Based on Emscripten's UTF8ToString with the following differences:
+ * - Always reads all bytes up to the given length, including null bytes. This
+ *   means that we can decode strings that contain null bytes in the middle.
+ * - Allow UTF-8 encoded code points that are part of a surrogate pair, even though
+ *   this is technically invalid UTF-8 that UTF8ToString would convert to 0xfffd.
+ */
+export default function HermesParserDecodeUTF8String(
+  ptrIn: number,
+  length: number,
+  heap: Uint8Array,
+): string {
+  let ptr = ptrIn;
+  const endPtr = ptr + length;
+  let str = '';
+
+  while (ptr < endPtr) {
+    // ASCII characters fit in single byte code point
+    let u0 = heap[ptr++];
+    if (!(u0 & 0x80)) {
+      str += String.fromCharCode(u0);
+      continue;
+    }
+
+    // Two byte code point
+    const u1 = heap[ptr++] & 0x3f;
+    if ((u0 & 0xe0) === 0xc0) {
+      str += String.fromCharCode(((u0 & 0x1f) << 6) | u1);
+      continue;
+    }
+
+    const u2 = heap[ptr++] & 0x3f;
+    if ((u0 & 0xf0) === 0xe0) {
+      // Three byte code point
+      u0 = ((u0 & 0x0f) << 12) | (u1 << 6) | u2;
+    } else {
+      // Four byte code point
+      u0 = ((u0 & 0x07) << 18) | (u1 << 12) | (u2 << 6) | (heap[ptr++] & 0x3f);
+    }
+
+    if (u0 < 0x10000) {
+      // Code point fits into a single UTF-16 code unit
+      str += String.fromCharCode(u0);
+    } else {
+      // Code point does not fit into single UTF-16 code unit so convert to surrogate pair
+      u0 -= 0x10000;
+      str += String.fromCharCode(0xd800 | (u0 >> 10), 0xdc00 | (u0 & 0x3ff));
+    }
+  }
+
+  return str;
+}