Function pow [src]

q = a ^ b r may not alias a. Asserts that r has enough limbs to store the result. Upper bound is calcPowLimbsBufferLen(a.bitCountAbs(), b). limbs_buffer is used for temporary storage. The amount required is given by calcPowLimbsBufferLen.

Prototype

pub fn pow(r: *Mutable, a: Const, b: u32, limbs_buffer: []Limb) void

Parameters

r: *Mutablea: Constb: u32limbs_buffer: []Limb

Source

  pub fn pow(r: *Mutable, a: Const, b: u32, limbs_buffer: []Limb) void {
    assert(r.limbs.ptr != a.limbs.ptr); // illegal aliasing

    // Handle all the trivial cases first
    switch (b) {
        0 => {
            // a^0 = 1
            return r.set(1);
        },
        1 => {
            // a^1 = a
            return r.copy(a);
        },
        else => {},
    }

    if (a.eqlZero()) {
        // 0^b = 0
        return r.set(0);
    } else if (a.limbs.len == 1 and a.limbs[0] == 1) {
        // 1^b = 1 and -1^b = ±1
        r.set(1);
        r.positive = a.positive or (b & 1) == 0;
        return;
    }

    // Here a>1 and b>1
    const needed_limbs = calcPowLimbsBufferLen(a.bitCountAbs(), b);
    assert(r.limbs.len >= needed_limbs);
    assert(limbs_buffer.len >= needed_limbs);

    llpow(r.limbs, a.limbs, b, limbs_buffer);

    r.normalize(needed_limbs);
    r.positive = a.positive or (b & 1) == 0;
}  