fem_tutos/node_modules/d3-scale/src/symlog.js

import {linearish} from "./linear.js";
import {copy, transformer} from "./continuous.js";
import {initRange} from "./init.js";

function transformSymlog(c) {
  return function(x) {
    return Math.sign(x) * Math.log1p(Math.abs(x / c));
  };
}

function transformSymexp(c) {
  return function(x) {
    return Math.sign(x) * Math.expm1(Math.abs(x)) * c;
  };
}

export function symlogish(transform) {
  var c = 1, scale = transform(transformSymlog(c), transformSymexp(c));

  scale.constant = function(_) {
    return arguments.length ? transform(transformSymlog(c = +_), transformSymexp(c)) : c;
  };

  return linearish(scale);
}

export default function symlog() {
  var scale = symlogish(transformer());

  scale.copy = function() {
    return copy(scale, symlog()).constant(scale.constant());
  };

  return initRange.apply(scale, arguments);
}