Function sub [src]

Subtract a field element

Prototype

pub inline fn sub(a: Fe, b: Fe) Fe

Parameters

a: Feb: Fe

Source

  pub inline fn sub(a: Fe, b: Fe) Fe {
    var fe = b;
    comptime var i = 0;
    inline while (i < 4) : (i += 1) {
        fe.limbs[i + 1] += fe.limbs[i] >> 51;
        fe.limbs[i] &= MASK51;
    }
    fe.limbs[0] += 19 * (fe.limbs[4] >> 51);
    fe.limbs[4] &= MASK51;
    fe.limbs[0] = (a.limbs[0] + 0xfffffffffffda) - fe.limbs[0];
    fe.limbs[1] = (a.limbs[1] + 0xffffffffffffe) - fe.limbs[1];
    fe.limbs[2] = (a.limbs[2] + 0xffffffffffffe) - fe.limbs[2];
    fe.limbs[3] = (a.limbs[3] + 0xffffffffffffe) - fe.limbs[3];
    fe.limbs[4] = (a.limbs[4] + 0xffffffffffffe) - fe.limbs[4];

    return fe;
}  