Function utf32ToString

src/common/input/TextDecoder.ts:26–43

(data: Uint32Array, start: number = 0, end: number = data.length)

 * in a loop (which is a lot faster).
 */
export function utf32ToString(data: Uint32Array, start: number = 0, end: number = data.length): string {
  let result = '';
  for (let i = start; i < end; ++i) {
    let codepoint = data[i];
    if (codepoint > 0xFFFF) {
      // JS strings are encoded as UTF16, thus a non BMP codepoint gets converted into a surrogate
      // pair conversion rules:
      //  - subtract 0x10000 from code point, leaving a 20 bit number
      //  - add high 10 bits to 0xD800  --> first surrogate
      //  - add low 10 bits to 0xDC00   --> second surrogate
      codepoint -= 0x10000;
      result += String.fromCharCode((codepoint >> 10) + 0xD800) + String.fromCharCode((codepoint % 0x400) + 0xDC00);
    } else {
      result += String.fromCharCode(codepoint);
    }
  }
  return result;
}

/**
 * StringToUtf32 - decodes UTF16 sequences into UTF32 codepoints.