lib: add egcd

1 files changed, 52 insertions, 0 deletions

diff --git a/lib/rsa_test.go b/lib/rsa_test.go
new file mode 100644
index 0000000..ee71755
--- /dev/null
+++ b/lib/rsa_test.go
@@ -0,0 +1,52 @@
+// Copyright © 2021 siddharth ravikumar <s@ricketyspace.net>
+// SPDX-License-Identifier: ISC
+
+package lib
+
+import (
+	"math/big"
+	"testing"
+)
+
+func TestEGCD(t *testing.T) {
+	a := big.NewInt(128)
+	b := big.NewInt(96)
+	r := egcd(a, b)
+	if r.Gcd.Cmp(big.NewInt(32)) != 0 {
+		t.Errorf("gcd(128, 96) != 32")
+	}
+	if r.X.Cmp(big.NewInt(1)) != 0 || r.Y.Cmp(big.NewInt(-1)) != 0 {
+		t.Errorf("bézout_coef(128, 96) != {1,-1}")
+	}
+
+	a = big.NewInt(360)
+	b = big.NewInt(210)
+	r = egcd(a, b)
+	if r.Gcd.Cmp(big.NewInt(30)) != 0 {
+		t.Errorf("gcd(360, 210) != 30")
+	}
+	if r.X.Cmp(big.NewInt(3)) != 0 || r.Y.Cmp(big.NewInt(-5)) != 0 {
+		t.Errorf("bézout_coef(360, 210) != {3,-5}")
+	}
+
+	a = big.NewInt(108)
+	b = big.NewInt(144)
+	r = egcd(a, b)
+	if r.Gcd.Cmp(big.NewInt(36)) != 0 {
+		t.Errorf("gcd(108, 144) != 36")
+	}
+	if r.X.Cmp(big.NewInt(-1)) != 0 || r.Y.Cmp(big.NewInt(1)) != 0 {
+		t.Errorf("bézout_coef(108, 144) != {-1,1}")
+	}
+
+	a = big.NewInt(240)
+	b = big.NewInt(46)
+	r = egcd(a, b)
+	if r.Gcd.Cmp(big.NewInt(2)) != 0 {
+		t.Errorf("gcd(240, 46) != 2")
+	}
+	if r.X.Cmp(big.NewInt(-9)) != 0 || r.Y.Cmp(big.NewInt(47)) != 0 {
+		t.Errorf("bézout_coef(240, 46) != {-9,47}")
+	}
+
+}