Add a macro for querying the byte order of SkPMColor.

include/core/SkPostConfig.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkPostConfig_DEFINED
@@ skipping 169 matching lines @@
         #define SK_B32_SHIFT    8
         #define SK_A32_SHIFT    0
     #else
         #define SK_R32_SHIFT    0
         #define SK_G32_SHIFT    8
         #define SK_B32_SHIFT    16
         #define SK_A32_SHIFT    24
     #endif
 #endif
 
+/**
+ * SK_PMCOLOR_BYTE_ORDER can be used to query the byte order of SkPMColor at compile time. The
+ * relationship between the byte order and shift values depends on machine endianness. If the shift
+ * order is R=0, G=8, B=16, A=24 then ((char*)&pmcolor)[0] will produce the R channel on a little
+ * endian machine and the A channel on a big endian machine. Thus, given those shifts values,
+ * SK_PMCOLOR_BYTE_ORDER(R,G,B,A) will be true on a little endian machine and
+ * SK_PMCOLOR_BYTE_ORDER(A,B,G,R) will be true on a big endian machine.
+ */
+#ifdef SK_CPU_BENDIAN
+    #define SK_PMCOLOR_BYTE_ORDER(C0, C1, C2, C3)     \
+        (SK_ ## C3 ## 32_SHIFT == 0  &&             \
+         SK_ ## C2 ## 32_SHIFT == 8  &&             \
+         SK_ ## C1 ## 32_SHIFT == 16 &&             \
+         SK_ ## C0 ## 32_SHIFT == 24)
+#else
+    #define SK_PMCOLOR_BYTE_ORDER(C0, C1, C2, C3)     \
+        (SK_ ## C0 ## 32_SHIFT == 0  &&             \
+         SK_ ## C1 ## 32_SHIFT == 8  &&             \
+         SK_ ## C2 ## 32_SHIFT == 16 &&             \
+         SK_ ## C3 ## 32_SHIFT == 24)
+#endif
+
 //  stdlib macros
 
 #if 0
 #if !defined(strlen) && defined(SK_DEBUG)
     extern size_t sk_strlen(const char*);
     #define strlen(s)   sk_strlen(s)
 #endif
 #ifndef sk_strcpy
     #define sk_strcpy(dst, src)     strcpy(dst, src)
 #endif
@@ skipping 132 matching lines @@
 #else
 #define SK_SIZE_T_SPECIFIER "%zu"
 #endif
 #endif
 
 //////////////////////////////////////////////////////////////////////
 
 #ifndef SK_ALLOW_STATIC_GLOBAL_INITIALIZERS
 #define SK_ALLOW_STATIC_GLOBAL_INITIALIZERS 1
 #endif