Correct drawing I;16 horizontal lines

Tests/test_imagedraw.py

@@ -783,9 +783,10 @@ def test_rectangle_I16(bbox: Coords) -> None:
     draw = ImageDraw.Draw(im)
 
     # Act
-    draw.rectangle(bbox, outline=0xFFFF)
+    draw.rectangle(bbox, outline=0xCDEF)
 
     # Assert
+    assert im.getpixel((X0, Y0)) == 0xCDEF
     assert_image_equal_tofile(im, "Tests/images/imagedraw_rectangle_I.tiff")
 
 

src/libImaging/Draw.c

@@ -104,8 +104,6 @@
 
 static inline void
 hline8(Imaging im, int x0, int y0, int x1, int ink, Imaging mask) {
-    int pixelwidth;
-
     if (y0 >= 0 && y0 < im->ysize) {
         if (x0 < 0) {
             x0 = 0;
@@ -118,20 +116,30 @@
             x1 = im->xsize - 1;
         }
         if (x0 <= x1) {
-            pixelwidth = strncmp(im->mode, "I;16", 4) == 0 ? 2 : 1;
-            if (mask == NULL) {
-                memset(
-                    im->image8[y0] + x0 * pixelwidth,
-                    (UINT8)ink,
-                    (x1 - x0 + 1) * pixelwidth
-                );
+            int bigendian = -1;
+            if (strncmp(im->mode, "I;16", 4) == 0) {
+                bigendian =
+                    (
+#ifdef WORDS_BIGENDIAN
+                        strcmp(im->mode, "I;16") == 0 || strcmp(im->mode, "I;16L") == 0
+#else
+                        strcmp(im->mode, "I;16B") == 0
+#endif
+                    )
+                        ? 1
+                        : 0;
+            }
+            if (mask == NULL && bigendian == -1) {
+                memset(im->image8[y0] + x0, (UINT8)ink, (x1 - x0 + 1));
             } else {
                 UINT8 *p = im->image8[y0];
                 while (x0 <= x1) {
-                    if (mask->image8[y0][x0]) {
-                        p[x0 * pixelwidth] = ink;
-                        if (pixelwidth == 2) {
-                            p[x0 * pixelwidth + 1] = ink;
+                    if (mask == NULL || mask->image8[y0][x0]) {
+                        if (bigendian == -1) {
+                            p[x0] = ink;
+                        } else {
+                            p[x0 * 2 + (bigendian ? 1 : 0)] = ink;
+                            p[x0 * 2 + (bigendian ? 0 : 1)] = ink >> 8;
                         }
                     }
                     x0++;