Initial commit

.gitignore

+# If you prefer the allow list template instead of the deny list, see community template:
+# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
+#
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+# Go workspace file
+go.work
\ No newline at end of file

README.md

+# Fermat Primality Test
+
+This small go program tests numbers for primality using the fermat primality test.
+
+## Getting started
+Simply start the program with:
+```bash
+go run cmd/fermatprimalitytest/main.go
+```
\ No newline at end of file

cmd/fermatprimalitytest/main.go

+package main
+
+// Importing packages
+import (
+	"fermatprimalitytest/internal"
+	"fmt"
+)
+
+// Main function
+func main() {
+	n := 341
+	fmt.Printf("n %d is (probably) prim: %t\n", n, internal.IsProbablyPrimFermat(n, 2))
+
+	fmt.Printf("n %d is (probably) prim: %t\n", n, internal.IsProbablyPrimFermatMulti(n, []int{2, 3}))
+}

go.mod

+module fermatprimalitytest
+
+go 1.18

internal/fermat-primality-test.go

+package internal
+
+import (
+	"fmt"
+	"math/big"
+)
+
+func IsProbablyPrimFermat(n int, a int) bool {
+	if n%a == 0 {
+		return false
+	}
+	var aExp big.Int
+	aExp.SetUint64(1)
+	for i := 0; i < (n - 1); i++ {
+		aExp = *aExp.Mul(&aExp, big.NewInt(int64(a)))
+	}
+
+	if aExp.Mod(&aExp, big.NewInt(int64(n))).Cmp(big.NewInt(int64(1))) == 0 {
+		return true
+	} else {
+		return false
+	}
+}
+
+func IsProbablyPrimFermatMulti(n int, bases []int) bool {
+	for _, base := range bases {
+		if n > base {
+			if IsProbablyPrimFermat(n, base) {
+				fmt.Printf("True with base: %d and value %d\n", base, n)
+			} else {
+				fmt.Printf("False with base: %d and value %d\n", base, n)
+				return false
+			}
+		}
+	}
+	return true
+}

internal/fermat-primality-test_test.go

+package internal
+
+import "testing"
+
+func TestIsProbablyPrimFermat(t *testing.T) {
+	tables := []struct {
+		n        int
+		a        int
+		expected bool
+	}{
+		{3, 2, true},
+		{4, 2, false},
+		{5, 2, true},
+		{9, 2, false},
+		{341, 2, true}, // Pseudeo prim
+		{341, 3, false},
+	}
+
+	for _, table := range tables {
+		res := IsProbablyPrimFermat(table.n, table.a)
+		if res != table.expected {
+			t.Errorf("Test of n: %d and a: %d was incorrect, got: %t, expected: %t.", table.n, table.a, res, table.expected)
+		} else {
+			t.Logf("Test of n: %d and a: %d was correct, got: %t, expected: %t.", table.n, table.a, res, table.expected)
+		}
+	}
+}
+
+func TestIsProbablyPrimFermatMulti(t *testing.T) {
+	tables := []struct {
+		n        int
+		bases    []int
+		expected bool
+	}{
+		{3, []int{2, 3}, true},
+		{4, []int{2, 3}, false},
+		{5, []int{2, 3}, true},
+		{9, []int{2, 3}, false},
+		{341, []int{2}, true}, // Pseudeo prim
+		{341, []int{2, 3}, false},
+	}
+
+	for _, table := range tables {
+		res := IsProbablyPrimFermatMulti(table.n, table.bases)
+		if res != table.expected {
+			t.Errorf("Test of n: %d and bases: %d was incorrect, got: %t, expected: %t.", table.n, table.bases, res, table.expected)
+		} else {
+			t.Logf("Test of n: %d and bases: %d was correct, got: %t, expected: %t.", table.n, table.bases, res, table.expected)
+		}
+	}
+}