copyFrom()

in backend/encoding.js [958:997]

• 28 lines of code
• 17 McCabe index (conditional complexity)

  copyFrom(decoder, options = {}) {
    if (options.sumValues) {
      throw new RangeError('unsupported options for DeltaEncoder.copyFrom()')
    }
    if (!(decoder instanceof DeltaDecoder)) {
      throw new TypeError('incompatible type of decoder')
    }

    let remaining = options.count
    if (remaining > 0 && decoder.done) throw new RangeError(`cannot copy ${remaining} values`)
    if (remaining === 0 || decoder.done) return

    // Copy any null values, and the first non-null value, so that appendValue() computes the
    // difference between the encoder's last value and the decoder's first (absolute) value.
    let value = decoder.readValue(), nulls = 0
    this.appendValue(value)
    if (value === null) {
      nulls = decoder.count + 1
      if (remaining !== undefined && remaining < nulls) nulls = remaining
      decoder.count -= nulls - 1
      this.count += nulls - 1
      if (remaining > nulls && decoder.done) throw new RangeError(`cannot copy ${remaining} values`)
      if (remaining === nulls || decoder.done) return

      // The next value read is certain to be non-null because we're not at the end of the decoder,
      // and a run of nulls must be followed by a run of non-nulls.
      if (decoder.count === 0) this.appendValue(decoder.readValue())
    }

    // Once we have the first value, the subsequent relative values can be copied verbatim without
    // any further processing. Note that the first value copied by super.copyFrom() is an absolute
    // value, while subsequent values are relative. Thus, the sum of all of the (non-null) copied
    // values must equal the absolute value of the final element copied.
    if (remaining !== undefined) remaining -= nulls + 1
    const { nonNullValues, sum } = super.copyFrom(decoder, {count: remaining, sumValues: true})
    if (nonNullValues > 0) {
      this.absoluteValue = sum
      decoder.absoluteValue = sum
    }
  }