Example #1
0
// Prime returns true if n is prime.
func (m *SPRP) Prime(n uint32) bool {
	for n >= m.limit {
		m.bx++
		m.limit = baseSets[m.bx].limit
	}
	m.bases = baseSets[m.bx].bases
	for i, a := range m.bases {
		m.maxP2[i] = 0
		m.basePow2[i][0] = uint64(a)
	}

	nm1 := n - 1
	s := xmath.TrailingZeros32(nm1)
	d := nm1 >> s
	for i, _ := range m.bases {
		// compute x := a^d % n
		n64 := uint64(n)
		x := uint64(1)
		p2 := m.basePow2[i][0:]
		bit := 0
		for dr := d; dr > 0; dr >>= 1 {
			if bit > m.maxP2[i] {
				p1 := p2[bit-1]
				p2[bit] = p1 * p1 % n64
				m.maxP2[i]++
			}
			if dr&1 != 0 {
				x = x * p2[bit] % n64
			}
			bit++
		}
		if x == 1 || uint32(x) == nm1 {
			continue
		}
		for r := byte(1); ; r++ {
			if r == s {
				return false
			}
			x = x * x % n64
			if x == 1 {
				return false
			}
			if uint32(x) == nm1 {
				break
			}
		}
	}
	return true
}
Example #2
0
func TestTrailingZeros32(t *testing.T) {
	for _, tc := range s {
		tc32 := uint32(tc)
		// seqential algorithm
		var tz byte
		if tc32 != 0 {
			for nz := tc32; nz&1 == 0; nz >>= 1 {
				tz++
			}
		}
		// test
		if cz := xmath.TrailingZeros32(tc32); cz != tz {
			t.Errorf("TrailingZero32(%x) expected %d, got %d", tc32, tz, cz)
		}
	}
}