wink-nlp/src/locate.js

Developer friendly Natural Language Processing ✨

//     wink-nlp
//
//     Copyright (C) GRAYPE Systems Private Limited
//
//     This file is part of “wink-nlp”.
//
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//     person obtaining a copy of this software and
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//     deal in the Software without restriction, including
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//     copies of the Software, and to permit persons to
//     whom the Software is furnished to do so, subject to
//     the following conditions:
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//     portions of the Software.
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//

// ## locate
/**
 *
 * Locates the `token`'s index in the `spans` and returns the index of the
 * span, where it is found; or the edge — a fraction between the 2-candidate
 * span-elements. Locate dictionary meaning: **discover the exact place or
 * position of.**
 *
 * @param {number} token to be located.
 * @param {array[]} spans where token will be searched.
 * @return {number} index of span where token is found; if it is not found then
 * it returns the edge — a fraction between the 2-candidate span-elements.
 * @private
*/
var locate = function ( token, spans ) {
  var minIndex = 0;
  var maxIndex = spans.length - 1;
  var currIndex;
  var leftToken;
  var rightToken;
  // Edge, if `token` is not found; they are converted to fractions using `sf`.
  var edge = -1;
  // `0.5` is a safe fraction as it is `2 ** -1`
  var sf = 0.5;
  while ( minIndex <= maxIndex ) {
    currIndex = ( minIndex + maxIndex ) / 2 | 0; // eslint-disable-line no-bitwise
    leftToken = spans[ currIndex ][ 0 ];
    rightToken = spans[ currIndex ][ 1 ];

    if ( token > rightToken ) {
      minIndex = currIndex + 1;
      edge = currIndex + sf;
    } else if ( token < leftToken ) {
      maxIndex = currIndex - 1;
      edge = currIndex - sf;
    } else return currIndex;
  }
  // Not found — return the edge!
  return edge;
}; // locate()

module.exports = locate;