in src/ristretto255.js [915:924]
function negateScalar(s) {
const negS = new Float64Array(64);
// neg_s := L - s
for (let i = 0; i < 32; i++) {
negS[i] = -s[i];
}
const o = new Uint8Array(32);
lowlevel.modL(o, negS);
return o;
}