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next.go
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next.go
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package prime
import (
"math"
"math/big"
)
// Next returns the next prime number after a given 64-bit number.
// It also returns a boolean value that is set to false if no
// prime number exists after the given number
// (not because there is no such number in the mathematical set of integers,
// but rather because there is no such number that can be represented
// by a 64-bit integer in Go).
func Next(n int64) (prime int64, exists bool) {
if n <= 1 {
prime, exists = 2, true
return
}
prime = n
for {
if prime == math.MaxInt64 {
prime = 0
break
}
prime++
if Is(prime) {
exists = true
break
}
}
return
}
// BigNext returns the next prime number after
// a given number of arbitrary size.
func BigNext(bigN *big.Int) (bigPrime *big.Int) {
if bigN.Cmp(bigOne) <= 0 {
bigPrime = big.NewInt(2)
return
}
bigPrime = (new(big.Int)).Set(bigN)
for {
bigPrime.Add(bigPrime, bigOne)
if BigIs(bigPrime) {
break
}
}
return
}
// NextAdditive returns the next additive prime number after a given 64-bit number.
// It also returns a boolean value that is set to false if no
// additive prime number exists after the given number
// (not because there is no such number in the mathematical set of integers,
// but rather because there is no such number that can be represented
// by a 64-bit integer in Go).
func NextAdditive(n int64) (additivePrime int64, exists bool) {
if n <= 1 {
additivePrime, exists = 2, true
return
}
additivePrime = n
for {
if additivePrime == math.MaxInt64 {
additivePrime = 0
break
}
additivePrime++
if IsAdditive(additivePrime) {
exists = true
break
}
}
return
}
// BigNextAdditive returns the next additive prime number
// after a given number of arbitrary size.
func BigNextAdditive(bigN *big.Int) (bigAdditivePrime *big.Int) {
if bigN.Cmp(bigOne) <= 0 {
bigAdditivePrime = big.NewInt(2)
return
}
bigAdditivePrime = (new(big.Int)).Set(bigN)
for {
bigAdditivePrime.Add(bigAdditivePrime, bigOne)
if BigIsAdditive(bigAdditivePrime) {
break
}
}
return
}