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node_modules/bson/src/utils/latin.ts

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+/**
+ * This function is an optimization for small basic latin strings.
+ * @internal
+ * @remarks
+ * ### Important characteristics:
+ * - If the uint8array or distance between start and end is 0 this function returns an empty string
+ * - If the byteLength of the string is 1, 2, or 3 we invoke String.fromCharCode and manually offset into the buffer
+ * - If the byteLength of the string is less than or equal to 20 an array of bytes is built and `String.fromCharCode.apply` is called with the result
+ * - If any byte exceeds 128 this function returns null
+ *
+ * @param uint8array - A sequence of bytes that may contain basic latin characters
+ * @param start - The start index from which to search the uint8array
+ * @param end - The index to stop searching the uint8array
+ * @returns string if all bytes are within the basic latin range, otherwise null
+ */
+export function tryReadBasicLatin(
+  uint8array: Uint8Array,
+  start: number,
+  end: number
+): string | null {
+  if (uint8array.length === 0) {
+    return '';
+  }
+
+  const stringByteLength = end - start;
+  if (stringByteLength === 0) {
+    return '';
+  }
+
+  if (stringByteLength > 20) {
+    return null;
+  }
+
+  if (stringByteLength === 1 && uint8array[start] < 128) {
+    return String.fromCharCode(uint8array[start]);
+  }
+
+  if (stringByteLength === 2 && uint8array[start] < 128 && uint8array[start + 1] < 128) {
+    return String.fromCharCode(uint8array[start]) + String.fromCharCode(uint8array[start + 1]);
+  }
+
+  if (
+    stringByteLength === 3 &&
+    uint8array[start] < 128 &&
+    uint8array[start + 1] < 128 &&
+    uint8array[start + 2] < 128
+  ) {
+    return (
+      String.fromCharCode(uint8array[start]) +
+      String.fromCharCode(uint8array[start + 1]) +
+      String.fromCharCode(uint8array[start + 2])
+    );
+  }
+
+  const latinBytes = [];
+  for (let i = start; i < end; i++) {
+    const byte = uint8array[i];
+    if (byte > 127) {
+      return null;
+    }
+    latinBytes.push(byte);
+  }
+
+  return String.fromCharCode(...latinBytes);
+}
+
+/**
+ * This function is an optimization for writing small basic latin strings.
+ * @internal
+ * @remarks
+ * ### Important characteristics:
+ * - If the string length is 0 return 0, do not perform any work
+ * - If a string is longer than 25 code units return null
+ * - If any code unit exceeds 128 this function returns null
+ *
+ * @param destination - The uint8array to serialize the string to
+ * @param source - The string to turn into UTF-8 bytes if it fits in the basic latin range
+ * @param offset - The position in the destination to begin writing bytes to
+ * @returns the number of bytes written to destination if all code units are below 128, otherwise null
+ */
+export function tryWriteBasicLatin(
+  destination: Uint8Array,
+  source: string,
+  offset: number
+): number | null {
+  if (source.length === 0) return 0;
+
+  if (source.length > 25) return null;
+
+  if (destination.length - offset < source.length) return null;
+
+  for (
+    let charOffset = 0, destinationOffset = offset;
+    charOffset < source.length;
+    charOffset++, destinationOffset++
+  ) {
+    const char = source.charCodeAt(charOffset);
+    if (char > 127) return null;
+
+    destination[destinationOffset] = char;
+  }
+
+  return source.length;
+}