From d51d03edd54d01aee638ac6f294c2ae105ff2929 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Thu, 15 Feb 2018 21:44:39 -0800
Subject: [PATCH] fix for BigEndian import

+ simplification of the logic

Change-Id: Ia20ce844793ed35ea03a17cef45838f3d0ae4afa
---

diff --git a/src/enc/picture_csp_enc.c b/src/enc/picture_csp_enc.c
index d531dd0..7444094 100644
--- a/src/enc/picture_csp_enc.c
+++ b/src/enc/picture_csp_enc.c
@@ -11,6 +11,10 @@
 //
 // Author: Skal (pascal.massimino@gmail.com)
 
+#ifdef HAVE_CONFIG_H
+#include "src/webp/config.h"
+#endif
+
 #include <assert.h>
 #include <stdlib.h>
 #include <math.h>
@@ -28,11 +32,11 @@
 // If defined, use table to compute x / alpha.
 #define USE_INVERSE_ALPHA_TABLE
 
-static const union {
-  uint32_t argb;
-  uint8_t  bytes[4];
-} test_endian = { 0xff000000u };
-#define ALPHA_IS_LAST (test_endian.bytes[3] == 0xff)
+#ifdef WORDS_BIGENDIAN
+#define ALPHA_OFFSET 0   // uint32_t 0xff000000 is 0xff,00,00,00 in memory
+#else
+#define ALPHA_OFFSET 3   // uint32_t 0xff000000 is 0x00,00,00,ff in memory
+#endif
 
 //------------------------------------------------------------------------------
 // Detection of non-trivial transparency
@@ -61,7 +65,7 @@
     return CheckNonOpaque(picture->a, picture->width, picture->height,
                           1, picture->a_stride);
   } else {
-    const int alpha_offset = ALPHA_IS_LAST ? 3 : 0;
+    const int alpha_offset = ALPHA_OFFSET;
     return CheckNonOpaque((const uint8_t*)picture->argb + alpha_offset,
                           picture->width, picture->height,
                           4, picture->argb_stride * sizeof(*picture->argb));
@@ -990,10 +994,10 @@
     return WebPEncodingSetError(picture, VP8_ENC_ERROR_INVALID_CONFIGURATION);
   } else {
     const uint8_t* const argb = (const uint8_t*)picture->argb;
-    const uint8_t* const r = ALPHA_IS_LAST ? argb + 2 : argb + 1;
-    const uint8_t* const g = ALPHA_IS_LAST ? argb + 1 : argb + 2;
-    const uint8_t* const b = ALPHA_IS_LAST ? argb + 0 : argb + 3;
-    const uint8_t* const a = ALPHA_IS_LAST ? argb + 3 : argb + 0;
+    const uint8_t* const a = argb + (0 ^ ALPHA_OFFSET);
+    const uint8_t* const r = argb + (1 ^ ALPHA_OFFSET);
+    const uint8_t* const g = argb + (2 ^ ALPHA_OFFSET);
+    const uint8_t* const b = argb + (3 ^ ALPHA_OFFSET);
 
     picture->colorspace = WEBP_YUV420;
     return ImportYUVAFromRGBA(r, g, b, a, 4, 4 * picture->argb_stride,
@@ -1044,7 +1048,8 @@
     const int argb_stride = 4 * picture->argb_stride;
     uint8_t* dst = (uint8_t*)picture->argb;
     const uint8_t *cur_u = picture->u, *cur_v = picture->v, *cur_y = picture->y;
-    WebPUpsampleLinePairFunc upsample = WebPGetLinePairConverter(ALPHA_IS_LAST);
+    WebPUpsampleLinePairFunc upsample =
+        WebPGetLinePairConverter(ALPHA_OFFSET > 0);
 
     // First row, with replicated top samples.
     upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, width);
@@ -1087,6 +1092,7 @@
                   const uint8_t* rgb, int rgb_stride,
                   int step, int swap_rb, int import_alpha) {
   int y;
+  // swap_rb -> b,g,r,a , !swap_rb -> r,g,b,a
   const uint8_t* r_ptr = rgb + (swap_rb ? 2 : 0);
   const uint8_t* g_ptr = rgb + 1;
   const uint8_t* b_ptr = rgb + (swap_rb ? 0 : 2);
@@ -1104,9 +1110,9 @@
   WebPInitAlphaProcessing();
 
   if (import_alpha) {
+    // dst[] byte order is {a,r,g,b} for big-endian, {b,g,r,a} for little endian
     uint32_t* dst = picture->argb;
-    const int do_copy =
-        (!swap_rb && !ALPHA_IS_LAST) || (swap_rb && ALPHA_IS_LAST);
+    const int do_copy = (ALPHA_OFFSET == 3) && swap_rb;
     assert(step == 4);
     for (y = 0; y < height; ++y) {
       if (do_copy) {