Function lookupRootElements

packages/intl-collator/compare.ts:202–232

(
  codePoints: readonly number[],
  start: number
)

}

function lookupRootElements(
  codePoints: readonly number[],
  start: number
): {elements: readonly PackedCollationElement[]; length: number} {
  const prefixMatch = lookupPrefixElements(codePoints, start)
  if (prefixMatch) {
    return prefixMatch
  }

  let node: PackedTrieNode | undefined = rootTrie
  let matchedElements: readonly PackedCollationElement[] | undefined
  let matchedLength = 0

  // UCA collation element lookup is longest-match so contractions such as
  // multi-code-point sequences beat their shorter prefixes.
  // https://www.unicode.org/reports/tr10/#Contractions
  for (let i = start; i < codePoints.length; i++) {
    node = node.next?.[codePoints[i]]
    if (!node) {
      break
    }
    if (node.value !== undefined) {
      matchedElements = rootElements[node.value]
      matchedLength = i - start + 1
    }
  }

  return matchedElements
    ? {elements: matchedElements, length: matchedLength}
    : {elements: [fallbackElement(codePoints[start])], length: 1}
}

function rootElementsForString(input: string): PackedCollationElement[] {
  const codePoints = stringToCodePoints(input)