/**
* Refer to https://cp-algorithms.com/string/string-hashing.html * @param {string} str * @param {number} p It is reasonable to make p a prime number roughly equal to * the number of characters in the input alphabet. Maybe 257 is a good choice. * @param {number} m Obviously m should be a large number, since the probability * of two random strings colliding is about 1/m. A good choice for m is some * large prime number, for example, 1e9+9 (1000000007 and 1000000009 are the * largest known pair of twin primes of the form [10^n + 7, 10^n + 9]. Refer to * https://primes.utm.edu/curios/page.php/1000000009.html) */
function polynomial_rolling_hash(str, p, m) {
let h = 0; let pow = 1; for (let i = 0; i < str.length; i++) { const c = str.charCodeAt(i); // h = (h + (c - 'a'.charCodeAt(0) + 1) * pow) % m; h = (h + c * pow) % m; pow = (pow * p) % m; } return h;
}
function invertColor(hex, bw) {
if (hex.indexOf('#') === 0) { hex = hex.slice(1); } // convert 3-digit hex to 6-digits. if (hex.length === 3) { hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2]; } if (hex.length !== 6) { throw new Error('Invalid HEX color.'); } var r = parseInt(hex.slice(0, 2), 16), g = parseInt(hex.slice(2, 4), 16), b = parseInt(hex.slice(4, 6), 16); if (bw) { // http://stackoverflow.com/a/3943023/112731 return (r * 0.299 + g * 0.587 + b * 0.114) > 186 ? '#000000' : '#FFFFFF'; } // invert color components r = (255 - r).toString(16); g = (255 - g).toString(16); b = (255 - b).toString(16); // pad each with zeros and return return "#" + padZero(r) + padZero(g) + padZero(b);
}
function padZero(str, len) {
len = len || 2; var zeros = new Array(len).join('0'); return (zeros + str).slice(-len);
}
function hashColor(str) {
const p = 257; const m = 1e9+9; color = (polynomial_rolling_hash(str, p, m) % 16777215).toString(16); return '#' + padZero(color, 6);
}
function setInvertedColor(className) {
let elems = document.getElementsByClassName(className); for (const elem of elems) { const bgColor = hashColor(elem.innerText); const color = invertColor(bgColor, true); elem.style['color'] = color; elem.style['background-color'] = bgColor; }
}