Implement Base64 without need of JDK8. (#78)

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/ContextUtils.kt

@@ -116,14 +116,7 @@ internal interface ContextUtils {
      */
     val String.globalHashBase64: String
         get() {
-            val bytes = this.toByteArray(Charsets.UTF_8)
-            val hashBytes = this.globalHashBytes
-
-            val base64Bytes = java.util.Base64.getEncoder().encode(globalHashBytes)
-            // TODO: do not use JRE for base64
-            // (it is impossible right now due to native interop limitations)
-
-            return String(base64Bytes, Charsets.US_ASCII)
+            return base64Encode(globalHashBytes)
         }
 
     /**

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/HashUtils.kt

@@ -21,4 +21,15 @@ internal fun globalHash(data: ByteArray, retValPlacement: Placement): GlobalHash
     return res
 }
 
+internal fun base64Encode(data: ByteArray): String {
+    memScoped {
+        val resultSize = 4 * data.size / 3 + 3 + 1
+        val result = alloc(NativeArray of Int8Box length resultSize)
+        val bytes = allocNativeArrayOf(data)
+        Base64Encode(bytes.ptr, data.size, result.ptr, resultSize)
+        // TODO: any better way to do that without two copies?
+        return CString.fromArray(result).toString()
+    }
+}
+
 internal class LocalHash(val value: Long) : ConstValue by Int64(value)