Function getChunkBegin

src/pkg/utils/istextorbinary.ts:104–144

(buf: Uint8Array, chunkBegin: number)

// @todo add documentation for these

function getChunkBegin(buf: Uint8Array, chunkBegin: number) {
  // If it's the beginning, just return.
  if (chunkBegin === 0) {
    return 0;
  }

  if (!isLaterByteOfUtf8(buf[chunkBegin])) {
    return chunkBegin;
  }

  let begin = chunkBegin - 3;

  if (begin >= 0) {
    if (isFirstByteOf4ByteChar(buf[begin])) {
      return begin;
    }
  }

  begin = chunkBegin - 2;

  if (begin >= 0) {
    if (isFirstByteOf4ByteChar(buf[begin]) || isFirstByteOf3ByteChar(buf[begin])) {
      return begin;
    }
  }

  begin = chunkBegin - 1;

  if (begin >= 0) {
    // Is it a 4-byte, 3-byte utf8 character?
    if (
      isFirstByteOf4ByteChar(buf[begin]) ||
      isFirstByteOf3ByteChar(buf[begin]) ||
      isFirstByteOf2ByteChar(buf[begin])
    ) {
      return begin;
    }
  }

  return -1;
}

function getChunkEnd(buf: Uint8Array, chunkEnd: number) {
  // If it's the end, just return.