// 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
}
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)
}
}
}
