Function d3_scale_log

explainshell/web/static/js/d3.v3.js:6486–6539

(linear, base, log, pow)

    return d3_scale_log(d3.scale.linear().domain([ 0, Math.LN10 ]), 10, d3_scale_logp, d3_scale_powp);
  };
  function d3_scale_log(linear, base, log, pow) {
    function scale(x) {
      return linear(log(x));
    }
    scale.invert = function(x) {
      return pow(linear.invert(x));
    };
    scale.domain = function(x) {
      if (!arguments.length) return linear.domain().map(pow);
      if (x[0] < 0) log = d3_scale_logn, pow = d3_scale_pown; else log = d3_scale_logp, 
      pow = d3_scale_powp;
      linear.domain(x.map(log));
      return scale;
    };
    scale.base = function(_) {
      if (!arguments.length) return base;
      base = +_;
      return scale;
    };
    scale.nice = function() {
      linear.domain(d3_scale_nice(linear.domain(), d3_scale_logNice(base)));
      return scale;
    };
    scale.ticks = function() {
      var extent = d3_scaleExtent(linear.domain()), ticks = [];
      if (extent.every(isFinite)) {
        var b = Math.log(base), i = Math.floor(extent[0] / b), j = Math.ceil(extent[1] / b), u = pow(extent[0]), v = pow(extent[1]), n = base % 1 ? 2 : base;
        if (log === d3_scale_logn) {
          ticks.push(-Math.pow(base, -i));
          for (;i++ < j; ) for (var k = n - 1; k > 0; k--) ticks.push(-Math.pow(base, -i) * k);
        } else {
          for (;i < j; i++) for (var k = 1; k < n; k++) ticks.push(Math.pow(base, i) * k);
          ticks.push(Math.pow(base, i));
        }
        for (i = 0; ticks[i] < u; i++) {}
        for (j = ticks.length; ticks[j - 1] > v; j--) {}
        ticks = ticks.slice(i, j);
      }
      return ticks;
    };
    scale.tickFormat = function(n, format) {
      if (arguments.length < 2) format = d3_scale_logFormat;
      if (!arguments.length) return format;
      var b = Math.log(base), k = Math.max(.1, n / scale.ticks().length), f = log === d3_scale_logn ? (e = -1e-12, 
      Math.floor) : (e = 1e-12, Math.ceil), e;
      return function(d) {
        return d / pow(b * f(log(d) / b + e)) <= k ? format(d) : "";
      };
    };
    scale.copy = function() {
      return d3_scale_log(linear.copy(), base, log, pow);
    };
    return d3_scale_linearRebind(scale, linear);
  }
  var d3_scale_logFormat = d3.format(".0e");
  function d3_scale_logp(x) {
    return Math.log(x < 0 ? 0 : x);