std/math/big: add Int.Bytes

Author: mertcandav

std/math/big/int.jule

@@ -923,6 +923,17 @@ impl Int {
 		ret buf
 	}
 
+	// Returns the absolute value of x as a big-endian byte slice.
+	//
+	// To use a fixed length slice, or a preallocated one, use [Int.FillBytes].
+	fn Bytes(*self): []byte {
+		// This function is may used in cryptographic operations. It must not leak
+		// anything but the Int's sign and bit size through side-channels. Any
+		// changes must be reviewed by a security expert.
+		mut buf := make([]byte, len(self.abs)*_S)
+		ret buf[bytesW(self.abs, buf):]
+	}
+
 	// Sets self to x.
 	fn SetU64(mut *self, x: u64) {
 		setWU64(&self.abs, x)

std/math/big/int_test.jule

@@ -225,4 +225,21 @@ fn testBinomial(t: &testing::T) {
 			t.Errorf("Binomial({}, {}) = {}; want {}", test.n, test.k, prod, test.want)
 		}
 	}
+}
+
+#test
+fn testSetBytes(t: &testing::T) {
+	for _, prime in primes {
+		let mut i: Int
+		i.SetStr(prime, 0)
+
+		bytes := i.Bytes()
+
+		let mut j: Int
+		j.SetBytes(bytes)
+
+		if i.Cmp(&j) != 0 {
+			t.Errorf("Failed: {}", prime)
+		}
+	}
 }