@antv/scale/src/util/pretty.ts

export default function pretty(min: number, max: number, n: number = 5) {

  const res = {
    max: 0,
    min: 0,
    ticks: [],
  };

  if (min === max) {
    return {
      max,
      min,
      ticks: [min],
    };
  }

  /*
    R pretty:
    https://svn.r-project.org/R/trunk/src/appl/pretty.c
    https://www.rdocumentation.org/packages/base/versions/3.5.2/topics/pretty
    */
  const h = 1.5; // high.u.bias
  const h5 = 0.5 + 1.5 * h; // u5.bias
  // 反正我也不会调参，跳过所有判断步骤
  const d = max - min;
  const c = d / n;
  // 当d非常小的时候触发，但似乎没什么用
  // const min_n = Math.floor(n / 3);
  // const shrink_sml = Math.pow(2, 5);
  // if (Math.log10(d) < -2) {
  //   c = (_.max([ Math.abs(max), Math.abs(min) ]) * shrink_sml) / min_n;
  // }

  const base = Math.pow(10, Math.floor(Math.log10(c)));
  const toFixed = base < 1 ? Math.ceil(Math.abs(Math.log10(base))) : 0;
  let unit = base;
  if (2 * base - c < h * (c - unit)) {
    unit = 2 * base;
    if (5 * base - c < h5 * (c - unit)) {
      unit = 5 * base;
      if (10 * base - c < h * (c - unit)) {
        unit = 10 * base;
      }
    }
  }
  const nu = Math.ceil(max / unit);
  const ns = Math.floor(min / unit);

  res.max = Math.max(nu * unit, max);
  res.min = Math.min(ns * unit, min);

  let x = Number.parseFloat((ns * unit).toFixed(toFixed));
  while (x < max) {
    res.ticks.push(x);
    x += unit;
    if (toFixed) {
      x = Number.parseFloat(x.toFixed(toFixed));
    }
  }
  res.ticks.push(x);

  return res;
}