1 files changed, 20 insertions, 6 deletions
diff --git a/generic/tclStringObj.c b/generic/tclStringObj.c
index c248749..c0d85a0 100644
--- a/generic/tclStringObj.c
+++ b/generic/tclStringObj.c
@@ -2694,12 +2694,26 @@ TclStringCatObjv(
     }
 
     if (binary) {
-	Tcl_SetByteArrayLength(objResultPtr, length);
-    }
-
-
-    while (objc--) {
-	Tcl_AppendObjToObj(objResultPtr, *objv++);
+	/* Efficiently produce a pure binary result */
+	unsigned char *dst;
+	int start;
+
+	Tcl_GetByteArrayFromObj(objResultPtr, &start);
+	dst = Tcl_SetByteArrayLength(objResultPtr, length) + start;
+	while (objc--) {
+	    Tcl_Obj *objPtr = *objv++;
+
+	    if (objPtr->bytes == NULL) {
+		int more;
+		unsigned char *src = Tcl_GetByteArrayFromObj(objPtr, &more);
+		memcpy(dst, src, (size_t) more);
+		dst += more;
+	    }
+	}
+    } else {
+	while (objc--) {
+	    Tcl_AppendObjToObj(objResultPtr, *objv++);
+	}
     }
     *objPtrPtr = objResultPtr;
     return TCL_OK;