source: node_modules/d3-format/src/formatPrefixAuto.js@ e4c61dd

import {formatDecimalParts} from "./formatDecimal.js";

export var prefixExponent;

export default function(x, p) {
  var d = formatDecimalParts(x, p);
  if (!d) return prefixExponent = undefined, x.toPrecision(p);
  var coefficient = d[0],
      exponent = d[1],
      i = exponent - (prefixExponent = Math.max(-8, Math.min(8, Math.floor(exponent / 3))) * 3) + 1,
      n = coefficient.length;
  return i === n ? coefficient
      : i > n ? coefficient + new Array(i - n + 1).join("0")
      : i > 0 ? coefficient.slice(0, i) + "." + coefficient.slice(i)
      : "0." + new Array(1 - i).join("0") + formatDecimalParts(x, Math.max(0, p + i - 1))[0]; // less than 1y!
}