trezor-firmware/ed25519-donna/curve25519-donna-scalarmult-base.h

/* Calculates nQ where Q is the x-coordinate of a point on the curve
 *
 *   mypublic: the packed little endian x coordinate of the resulting curve point
 *   n: a little endian, 32-byte number
 *   basepoint: a packed little endian point of the curve
 */

void curve25519_scalarmult_donna(curve25519_key mypublic, const curve25519_key n, const curve25519_key basepoint);