Detect Endian of ARGB image.

BUG=375
TESTED=libyuv builds, but no test app for it yet
R=harryjin@google.com

Review URL: https://webrtc-codereview.appspot.com/32389004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1154 16f28f9a-4ce2-e073-06de-1de4eb20be90

include/libyuv/compare.h

@@ -22,6 +22,11 @@ extern "C" {
 LIBYUV_API
 uint32 HashDjb2(const uint8* src, uint64 count, uint32 seed);
 
+// Scan an opaque argb image and return fourcc based on alpha offset.
+// Returns FOURCC_ARGB, FOURCC_BGRA, or 0 if unknown.
+LIBYUV_API
+uint32 ARGBDetect(const uint8* argb, int stride_argb, int width, int height);
+
 // Sum Square Error - used to compute Mean Square Error or PSNR.
 LIBYUV_API
 uint64 ComputeSumSquareError(const uint8* src_a,

source/compare.cc

@@ -19,6 +19,7 @@
 #include "libyuv/basic_types.h"
 #include "libyuv/cpu_id.h"
 #include "libyuv/row.h"
+#include "libyuv/video_common.h"
 
 #ifdef __cplusplus
 namespace libyuv {
@@ -78,6 +79,40 @@ uint32 HashDjb2(const uint8* src, uint64 count, uint32 seed) {
   return seed;
 }
 
+static uint32 ARGBDetectRow_C(const uint8* argb, int width) {
+  int x;
+  for (x = 0; x < width; ++x) {
+    if (argb[0] != 255) {  // First byte is not Alpha of 255, so not ARGB.
+      return FOURCC_BGRA;
+    }
+    if (argb[3] != 255) {  // 4th byte is not Alpha of 255, so not BGRA.
+      return FOURCC_ARGB;
+    }
+    argb += 4;
+  }
+  return 0;
+}
+
+// Scan an opaque argb image and return fourcc based on alpha offset.
+// Returns FOURCC_ARGB, FOURCC_BGRA, or 0 if unknown.
+LIBYUV_API
+uint32 ARGBDetect(const uint8* argb, int stride_argb, int width, int height) {
+  uint32 fourcc = 0;
+  int h;
+
+  // Coalesce rows.
+  if (stride_argb == width * 4) {
+    width *= height;
+    height = 1;
+    stride_argb = 0;
+  }
+  for (h = 0; h < height && fourcc == 0; ++h) {
+    fourcc = ARGBDetectRow_C(argb, width);
+    argb += stride_argb;
+  }
+  return fourcc;
+}
+
 uint32 SumSquareError_C(const uint8* src_a, const uint8* src_b, int count);
 #if !defined(LIBYUV_DISABLE_NEON) && \
     (defined(__ARM_NEON__) || defined(LIBYUV_NEON) || defined(__aarch64__))

unit_test/compare_test.cc

@@ -17,6 +17,7 @@
 #include "libyuv/compare.h"
 #include "libyuv/cpu_id.h"
 #include "libyuv/row.h"
+#include "libyuv/video_common.h"
 
 namespace libyuv {
 
@@ -146,6 +147,34 @@ TEST_F(libyuvTest, BenchmarkDjb2_Unaligned) {
   free_aligned_buffer_64(src_a);
 }
 
+TEST_F(libyuvTest, BenchmarkARGBDetect_Opt) {
+  uint32 fourcc;
+  const int kMaxTest = benchmark_width_ * benchmark_height_ * 4;
+  align_buffer_64(src_a, kMaxTest);
+  for (int i = 0; i < kMaxTest; ++i) {
+    src_a[i] = 255;
+  }
+
+  src_a[0] = 0;
+  fourcc = ARGBDetect(src_a, benchmark_width_ * 4,
+                      benchmark_width_, benchmark_height_);
+  EXPECT_EQ(libyuv::FOURCC_BGRA, fourcc);
+  src_a[0] = 255;
+  src_a[3] = 0;
+  fourcc = ARGBDetect(src_a, benchmark_width_ * 4,
+                      benchmark_width_, benchmark_height_);
+  EXPECT_EQ(libyuv::FOURCC_ARGB, fourcc);
+  src_a[3] = 255;
+
+  for (int i = 0; i < benchmark_iterations_; ++i) {
+    fourcc = ARGBDetect(src_a, benchmark_width_ * 4,
+                        benchmark_width_, benchmark_height_);
+  }
+  EXPECT_EQ(0, fourcc);
+
+  free_aligned_buffer_64(src_a);
+}
+
 TEST_F(libyuvTest, BenchmarkSumSquareError_Opt) {
   const int kMaxWidth = 4096 * 3;
   align_buffer_64(src_a, kMaxWidth);