don't use memcpy when converting BGR;15/16

Author: Yay295

src/libImaging/Convert.c

@@ -280,24 +280,26 @@ rgb2f(UINT8 *out_, const UINT8 *in, int xsize) {
 }
 
 static void
-rgb2bgr15(UINT8 *out_, const UINT8 *in, int xsize) {
+rgb2bgr15(UINT8 *out, const UINT8 *in, int xsize) {
     int x;
-    for (x = 0; x < xsize; x++, in += 4, out_ += 2) {
-        UINT16 v = ((((UINT16)in[0]) << 7) & 0x7c00) +
-                   ((((UINT16)in[1]) << 2) & 0x03e0) +
-                   ((((UINT16)in[2]) >> 3) & 0x001f);
-        memcpy(out_, &v, sizeof(v));
+    for (x = 0; x < xsize; x++, in += 4, out += 2) {
+        const UINT8 r = in[0] >> 3;
+        const UINT8 g = in[1] >> 3;
+        const UINT8 b = in[2] >> 3;
+        out[1] = 0x80 | (b << 2) | (g >> 3);
+        out[0] = (g << 5) | r;
     }
 }
 
 static void
-rgb2bgr16(UINT8 *out_, const UINT8 *in, int xsize) {
+rgb2bgr16(UINT8 *out, const UINT8 *in, int xsize) {
     int x;
-    for (x = 0; x < xsize; x++, in += 4, out_ += 2) {
-        UINT16 v = ((((UINT16)in[0]) << 8) & 0xf800) +
-                   ((((UINT16)in[1]) << 3) & 0x07e0) +
-                   ((((UINT16)in[2]) >> 3) & 0x001f);
-        memcpy(out_, &v, sizeof(v));
+    for (x = 0; x < xsize; x++, in += 4, out += 2) {
+        const UINT8 r = in[0] >> 3;
+        const UINT8 g = in[1] >> 2;
+        const UINT8 b = in[2] >> 3;
+        out[1] = (b << 3) | (g >> 3);
+        out[0] = (g << 5) | r;
     }
 }