hash funtion for comparing images

BUG=none
TEST=none
Review URL: https://webrtc-codereview.appspot.com/380006

git-svn-id: http://libyuv.googlecode.com/svn/trunk@166 16f28f9a-4ce2-e073-06de-1de4eb20be90

include/libyuv/compare.h

@@ -18,39 +18,43 @@ namespace libyuv {
 extern "C" {
 #endif
 
-static const int kMaxPsnr = 128;
-
-double SumSquareErrorToPsnr(uint64 sse, uint64 count);
+// Compute a hash for specified memory.  Seed of 5381 recommended.
+uint32 HashDjb2(const uint8* src, uint64 count, uint32 seed);
 
-uint64 ComputeSumSquareError(const uint8 *src_a,
-                             const uint8 *src_b, int count);
+// Sum Square Error - used to compute Mean Square Error or PSNR
+uint64 ComputeSumSquareError(const uint8* src_a,
+                             const uint8* src_b, int count);
 
-uint64 ComputeSumSquareErrorPlane(const uint8 *src_a, int stride_a,
-                                  const uint8 *src_b, int stride_b,
+uint64 ComputeSumSquareErrorPlane(const uint8* src_a, int stride_a,
+                                  const uint8* src_b, int stride_b,
                                   int width, int height);
 
-double CalcFramePsnr(const uint8 *src_a, int stride_a,
-                     const uint8 *src_b, int stride_b,
-                     int width, int height);
+static const int kMaxPsnr = 128;
 
-double CalcFrameSsim(const uint8 *src_a, int stride_a,
-                     const uint8 *src_b, int stride_b,
+double SumSquareErrorToPsnr(uint64 sse, uint64 count);
+
+double CalcFramePsnr(const uint8* src_a, int stride_a,
+                     const uint8* src_b, int stride_b,
                      int width, int height);
 
-double I420Psnr(const uint8 *src_y_a, int stride_y_a,
-                const uint8 *src_u_a, int stride_u_a,
-                const uint8 *src_v_a, int stride_v_a,
-                const uint8 *src_y_b, int stride_y_b,
-                const uint8 *src_u_b, int stride_u_b,
-                const uint8 *src_v_b, int stride_v_b,
+double I420Psnr(const uint8* src_y_a, int stride_y_a,
+                const uint8* src_u_a, int stride_u_a,
+                const uint8* src_v_a, int stride_v_a,
+                const uint8* src_y_b, int stride_y_b,
+                const uint8* src_u_b, int stride_u_b,
+                const uint8* src_v_b, int stride_v_b,
                 int width, int height);
 
-double I420Ssim(const uint8 *src_y_a, int stride_y_a,
-                const uint8 *src_u_a, int stride_u_a,
-                const uint8 *src_v_a, int stride_v_a,
-                const uint8 *src_y_b, int stride_y_b,
-                const uint8 *src_u_b, int stride_u_b,
-                const uint8 *src_v_b, int stride_v_b,
+double CalcFrameSsim(const uint8* src_a, int stride_a,
+                     const uint8* src_b, int stride_b,
+                     int width, int height);
+
+double I420Ssim(const uint8* src_y_a, int stride_y_a,
+                const uint8* src_u_a, int stride_u_a,
+                const uint8* src_v_a, int stride_v_a,
+                const uint8* src_y_b, int stride_y_b,
+                const uint8* src_u_b, int stride_u_b,
+                const uint8* src_v_b, int stride_v_b,
                 int width, int height);
 
 #ifdef __cplusplus

source/compare.cc

@@ -22,6 +22,17 @@ namespace libyuv {
 extern "C" {
 #endif
 
+// hash seed of 5381 recommended.
+uint32 HashDjb2(const uint8* src, size_t len, uint32 seed) {
+  uint32 hash = seed;
+  if (len > 0) {
+    do {
+      hash = hash * 33 + *src++;
+    } while (--len);
+  }
+  return hash;
+}
+
 #if defined(__ARM_NEON__) && !defined(YUV_DISABLE_ASM)
 #define HAS_SUMSQUAREERROR_NEON
 
@@ -181,21 +192,23 @@ uint64 ComputeSumSquareError(const uint8* src_a,
   }
   const int kBlockSize = 32768;
   uint64 sse = 0;
-  while (count >= kBlockSize) {
-    sse += SumSquareError(src_a, src_b, kBlockSize);
-    src_a += kBlockSize;
-    src_b += kBlockSize;
-    count -= kBlockSize;
+#ifdef _OPENMP
+#pragma omp parallel for reduction(+: sse)
+#endif
+  for (int i = 0; i < (count - (kBlockSize - 1)); i += kBlockSize) {
+    sse += SumSquareError(src_a + i, src_b + i, kBlockSize);
   }
-  int remainder = count & ~15;
+  src_a += count & ~(kBlockSize - 1);
+  src_b += count & ~(kBlockSize - 1);
+  int remainder = count & (kBlockSize - 1) & ~15;
   if (remainder) {
     sse += SumSquareError(src_a, src_b, remainder);
     src_a += remainder;
     src_b += remainder;
-    count -= remainder;
   }
-  if (count) {
-    sse += SumSquareError_C(src_a, src_b, count);
+  remainder = count & 15;
+  if (remainder) {
+    sse += SumSquareError_C(src_a, src_b, remainder);
   }
   return sse;
 }