gotosocial/vendor/modernc.org/mathutil/primes.go
kim ed46224573
Add SQLite support, fix un-thread-safe DB caches, small performance f… (#172)
* Add SQLite support, fix un-thread-safe DB caches, small performance fixes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add SQLite licenses to README

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* appease the linter, and fix my dumbass-ery

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* make requested changes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add back comment

Signed-off-by: kim (grufwub) <grufwub@gmail.com>
2021-08-29 16:41:41 +02:00

332 lines
6.6 KiB
Go

// Copyright (c) 2014 The mathutil Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package mathutil // import "modernc.org/mathutil"
import (
"math"
)
// IsPrimeUint16 returns true if n is prime. Typical run time is few ns.
func IsPrimeUint16(n uint16) bool {
return n > 0 && primes16[n-1] == 1
}
// NextPrimeUint16 returns first prime > n and true if successful or an
// undefined value and false if there is no next prime in the uint16 limits.
// Typical run time is few ns.
func NextPrimeUint16(n uint16) (p uint16, ok bool) {
return n + uint16(primes16[n]), n < 65521
}
// IsPrime returns true if n is prime. Typical run time is about 100 ns.
func IsPrime(n uint32) bool {
switch {
case n&1 == 0:
return n == 2
case n%3 == 0:
return n == 3
case n%5 == 0:
return n == 5
case n%7 == 0:
return n == 7
case n%11 == 0:
return n == 11
case n%13 == 0:
return n == 13
case n%17 == 0:
return n == 17
case n%19 == 0:
return n == 19
case n%23 == 0:
return n == 23
case n%29 == 0:
return n == 29
case n%31 == 0:
return n == 31
case n%37 == 0:
return n == 37
case n%41 == 0:
return n == 41
case n%43 == 0:
return n == 43
case n%47 == 0:
return n == 47
case n%53 == 0:
return n == 53 // Benchmarked optimum
case n < 65536:
// use table data
return IsPrimeUint16(uint16(n))
default:
mod := ModPowUint32(2, (n+1)/2, n)
if mod != 2 && mod != n-2 {
return false
}
blk := &lohi[n>>24]
lo, hi := blk.lo, blk.hi
for lo <= hi {
index := (lo + hi) >> 1
liar := liars[index]
switch {
case n > liar:
lo = index + 1
case n < liar:
hi = index - 1
default:
return false
}
}
return true
}
}
// IsPrimeUint64 returns true if n is prime. Typical run time is few tens of µs.
//
// SPRP bases: http://miller-rabin.appspot.com
func IsPrimeUint64(n uint64) bool {
switch {
case n%2 == 0:
return n == 2
case n%3 == 0:
return n == 3
case n%5 == 0:
return n == 5
case n%7 == 0:
return n == 7
case n%11 == 0:
return n == 11
case n%13 == 0:
return n == 13
case n%17 == 0:
return n == 17
case n%19 == 0:
return n == 19
case n%23 == 0:
return n == 23
case n%29 == 0:
return n == 29
case n%31 == 0:
return n == 31
case n%37 == 0:
return n == 37
case n%41 == 0:
return n == 41
case n%43 == 0:
return n == 43
case n%47 == 0:
return n == 47
case n%53 == 0:
return n == 53
case n%59 == 0:
return n == 59
case n%61 == 0:
return n == 61
case n%67 == 0:
return n == 67
case n%71 == 0:
return n == 71
case n%73 == 0:
return n == 73
case n%79 == 0:
return n == 79
case n%83 == 0:
return n == 83
case n%89 == 0:
return n == 89 // Benchmarked optimum
case n <= math.MaxUint16:
return IsPrimeUint16(uint16(n))
case n <= math.MaxUint32:
return ProbablyPrimeUint32(uint32(n), 11000544) &&
ProbablyPrimeUint32(uint32(n), 31481107)
case n < 105936894253:
return ProbablyPrimeUint64_32(n, 2) &&
ProbablyPrimeUint64_32(n, 1005905886) &&
ProbablyPrimeUint64_32(n, 1340600841)
case n < 31858317218647:
return ProbablyPrimeUint64_32(n, 2) &&
ProbablyPrimeUint64_32(n, 642735) &&
ProbablyPrimeUint64_32(n, 553174392) &&
ProbablyPrimeUint64_32(n, 3046413974)
case n < 3071837692357849:
return ProbablyPrimeUint64_32(n, 2) &&
ProbablyPrimeUint64_32(n, 75088) &&
ProbablyPrimeUint64_32(n, 642735) &&
ProbablyPrimeUint64_32(n, 203659041) &&
ProbablyPrimeUint64_32(n, 3613982119)
default:
return ProbablyPrimeUint64_32(n, 2) &&
ProbablyPrimeUint64_32(n, 325) &&
ProbablyPrimeUint64_32(n, 9375) &&
ProbablyPrimeUint64_32(n, 28178) &&
ProbablyPrimeUint64_32(n, 450775) &&
ProbablyPrimeUint64_32(n, 9780504) &&
ProbablyPrimeUint64_32(n, 1795265022)
}
}
// NextPrime returns first prime > n and true if successful or an undefined value and false if there
// is no next prime in the uint32 limits. Typical run time is about 2 µs.
func NextPrime(n uint32) (p uint32, ok bool) {
switch {
case n < 65521:
p16, _ := NextPrimeUint16(uint16(n))
return uint32(p16), true
case n >= math.MaxUint32-4:
return
}
n++
var d0, d uint32
switch mod := n % 6; mod {
case 0:
d0, d = 1, 4
case 1:
d = 4
case 2, 3, 4:
d0, d = 5-mod, 2
case 5:
d = 2
}
p = n + d0
if p < n { // overflow
return
}
for {
if IsPrime(p) {
return p, true
}
p0 := p
p += d
if p < p0 { // overflow
break
}
d ^= 6
}
return
}
// NextPrimeUint64 returns first prime > n and true if successful or an undefined value and false if there
// is no next prime in the uint64 limits. Typical run time is in hundreds of µs.
func NextPrimeUint64(n uint64) (p uint64, ok bool) {
switch {
case n < 65521:
p16, _ := NextPrimeUint16(uint16(n))
return uint64(p16), true
case n >= 18446744073709551557: // last uint64 prime
return
}
n++
var d0, d uint64
switch mod := n % 6; mod {
case 0:
d0, d = 1, 4
case 1:
d = 4
case 2, 3, 4:
d0, d = 5-mod, 2
case 5:
d = 2
}
p = n + d0
if p < n { // overflow
return
}
for {
if ok = IsPrimeUint64(p); ok {
break
}
p0 := p
p += d
if p < p0 { // overflow
break
}
d ^= 6
}
return
}
// FactorTerm is one term of an integer factorization.
type FactorTerm struct {
Prime uint32 // The divisor
Power uint32 // Term == Prime^Power
}
// FactorTerms represent a factorization of an integer
type FactorTerms []FactorTerm
// FactorInt returns prime factorization of n > 1 or nil otherwise.
// Resulting factors are ordered by Prime. Typical run time is few µs.
func FactorInt(n uint32) (f FactorTerms) {
switch {
case n < 2:
return
case IsPrime(n):
return []FactorTerm{{n, 1}}
}
f, w := make([]FactorTerm, 9), 0
for p := 2; p < len(primes16); p += int(primes16[p]) {
if uint(p*p) > uint(n) {
break
}
power := uint32(0)
for n%uint32(p) == 0 {
n /= uint32(p)
power++
}
if power != 0 {
f[w] = FactorTerm{uint32(p), power}
w++
}
if n == 1 {
break
}
}
if n != 1 {
f[w] = FactorTerm{n, 1}
w++
}
return f[:w]
}
// PrimorialProductsUint32 returns a slice of numbers in [lo, hi] which are a
// product of max 'max' primorials. The slice is not sorted.
//
// See also: http://en.wikipedia.org/wiki/Primorial
func PrimorialProductsUint32(lo, hi, max uint32) (r []uint32) {
lo64, hi64 := int64(lo), int64(hi)
if max > 31 { // N/A
max = 31
}
var f func(int64, int64, uint32)
f = func(n, p int64, emax uint32) {
e := uint32(1)
for n <= hi64 && e <= emax {
n *= p
if n >= lo64 && n <= hi64 {
r = append(r, uint32(n))
}
if n < hi64 {
p, _ := NextPrime(uint32(p))
f(n, int64(p), e)
}
e++
}
}
f(1, 2, max)
return
}