Optimize Encode function

Author: Keelan10

kem/ntruprime/internal/Encode.go

@@ -1,8 +1,34 @@
 package internal
 
-// TO DO: Optimize the Encode function
 /* 0 <= R[i] < M[i] < 16384 */
 func Encode(out []uint8, R []uint16, M []uint16, len int) {
+	if len > 1 {
+		R2 := make([]uint16, (len+1)/2)
+		M2 := make([]uint16, (len+1)/2)
+		var i int
+		for ; len > 1; len = (len + 1) / 2 {
+			for i = 0; i < len-1; i += 2 {
+				m0 := uint32(M[i])
+				r := uint32(R[i]) + uint32(R[i+1])*m0
+				m := uint32(M[i+1]) * m0
+				for m >= 16384 {
+					out[0] = uint8(r)
+					out = out[1:]
+
+					r >>= 8
+					m = (m + 255) >> 8
+				}
+				R2[i/2] = uint16(r)
+				M2[i/2] = uint16(m)
+			}
+			if i < len {
+				R2[i/2] = R[i]
+				M2[i/2] = M[i]
+			}
+			copy(R, R2)
+			copy(M, M2)
+		}
+	}
 	if len == 1 {
 		r := R[0]
 		m := M[0]
@@ -13,29 +39,4 @@ func Encode(out []uint8, R []uint16, M []uint16, len int) {
 			m = (m + 255) >> 8
 		}
 	}
-	if len > 1 {
-		R2 := make([]uint16, (len+1)/2)
-		M2 := make([]uint16, (len+1)/2)
-		var i int
-
-		for i = 0; i < len-1; i += 2 {
-			m0 := uint32(M[i])
-			r := uint32(R[i]) + uint32(R[i+1])*m0
-			m := uint32(M[i+1]) * m0
-			for m >= 16384 {
-				out[0] = uint8(r)
-				out = out[1:]
-
-				r >>= 8
-				m = (m + 255) >> 8
-			}
-			R2[i/2] = uint16(r)
-			M2[i/2] = uint16(m)
-		}
-		if i < len {
-			R2[i/2] = R[i]
-			M2[i/2] = M[i]
-		}
-		Encode(out, R2, M2, (len+1)/2)
-	}
 }