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const SPACE = /[^ ]+/g
// Field-length norm: the shorter the field, the higher the weight.// Set to 3 decimals to reduce index size.export default function norm(mantissa = 3) {  const cache = new Map()
  return {    get(value) {      const numTokens = value.match(SPACE).length
      if (cache.has(numTokens)) {        return cache.get(numTokens)      }
      const n = parseFloat((1 / Math.sqrt(numTokens)).toFixed(mantissa))
      cache.set(numTokens, n)
      return n    },    clear() {      cache.clear()    }  }}