sse2 version of CollectHistogram()

~3% faster encoding.

Patch by Christian Duvivier (cduvivier at google dot com)

Change-Id: I8c11d63d0cffb35e145fe0ea74cb66a53f4950d9

src/enc/analysis.c

@@ -20,51 +20,12 @@
 extern "C" {
 #endif
 
-#define MAX_COEFF_THRESH   64
 #define MAX_ITERS_K_MEANS  6
 
-//-----------------------------------------------------------------------------
-// Compute susceptibility based on DCT-coeff histograms:
-// the higher, the "easier" the macroblock is to compress.
-
 static int ClipAlpha(int alpha) {
   return alpha < 0 ? 0 : alpha > 255 ? 255 : alpha;
 }
 
-static int GetAlpha(const int histo[MAX_COEFF_THRESH]) {
-  int num = 0, den = 0, val = 0;
-  int k;
-  int alpha;
-  for (k = 0; k < MAX_COEFF_THRESH; ++k) {
-    if (histo[k]) {
-      val += histo[k];
-      num += val * (k + 1);
-      den += (k + 1) * (k + 1);
-    }
-  }
-  // we scale the value to a usable [0..255] range
-  alpha = den ? 10 * num / den - 5 : 0;
-  return ClipAlpha(alpha);
-}
-
-static int CollectHistogram(const uint8_t* ref, const uint8_t* pred,
-                            int start_block, int end_block) {
-  int histo[MAX_COEFF_THRESH] = { 0 };
-  int16_t out[16];
-  int j, k;
-  for (j = start_block; j < end_block; ++j) {
-    VP8FTransform(ref + VP8Scan[j], pred + VP8Scan[j], out);
-    for (k = 0; k < 16; ++k) {
-      const int v = abs(out[k]) >> 2;
-      if (v) {
-        const int bin = (v > MAX_COEFF_THRESH) ? MAX_COEFF_THRESH : v;
-        histo[bin - 1]++;
-      }
-    }
-  }
-  return GetAlpha(histo);
-}
-
 //-----------------------------------------------------------------------------
 // Smooth the segment map by replacing isolated block by the majority of its
 // neighbours.
@@ -278,7 +239,7 @@ static int MBAnalyzeBestIntra16Mode(VP8EncIterator* const it) {
 
   VP8MakeLuma16Preds(it);
   for (mode = 0; mode < max_mode; ++mode) {
-    const int alpha = CollectHistogram(it->yuv_in_ + Y_OFF,
+    const int alpha = VP8CollectHistogram(it->yuv_in_ + Y_OFF,
                                           it->yuv_p_ + VP8I16ModeOffsets[mode],
                                           0, 16);
     if (alpha > best_alpha) {
@@ -303,7 +264,7 @@ static int MBAnalyzeBestIntra4Mode(VP8EncIterator* const it,
 
     VP8MakeIntra4Preds(it);
     for (mode = 0; mode < max_mode; ++mode) {
-      const int alpha = CollectHistogram(src,
+      const int alpha = VP8CollectHistogram(src,
                                             it->yuv_p_ + VP8I4ModeOffsets[mode],
                                             0, 1);
       if (alpha > best_mode_alpha) {
@@ -329,7 +290,7 @@ static int MBAnalyzeBestUVMode(VP8EncIterator* const it) {
   int mode;
   VP8MakeChroma8Preds(it);
   for (mode = 0; mode < max_mode; ++mode) {
-    const int alpha = CollectHistogram(it->yuv_in_ + U_OFF,
+    const int alpha = VP8CollectHistogram(it->yuv_in_ + U_OFF,
                                           it->yuv_p_ + VP8UVModeOffsets[mode],
                                           16, 16 + 4 + 4);
     if (alpha > best_alpha) {

src/enc/dsp.c

@@ -16,6 +16,48 @@
 extern "C" {
 #endif
 
+//-----------------------------------------------------------------------------
+// Compute susceptibility based on DCT-coeff histograms:
+// the higher, the "easier" the macroblock is to compress.
+
+static int ClipAlpha(int alpha) {
+  return alpha < 0 ? 0 : alpha > 255 ? 255 : alpha;
+}
+
+static int GetAlpha(const int histo[MAX_COEFF_THRESH]) {
+  int num = 0, den = 0, val = 0;
+  int k;
+  int alpha;
+  for (k = 0; k < MAX_COEFF_THRESH; ++k) {
+    if (histo[k]) {
+      val += histo[k];
+      num += val * (k + 1);
+      den += (k + 1) * (k + 1);
+    }
+  }
+  // we scale the value to a usable [0..255] range
+  alpha = den ? 10 * num / den - 5 : 0;
+  return ClipAlpha(alpha);
+}
+
+static int CollectHistogram(const uint8_t* ref, const uint8_t* pred,
+                            int start_block, int end_block) {
+  int histo[MAX_COEFF_THRESH] = { 0 };
+  int16_t out[16];
+  int j, k;
+  for (j = start_block; j < end_block; ++j) {
+    VP8FTransform(ref + VP8Scan[j], pred + VP8Scan[j], out);
+    for (k = 0; k < 16; ++k) {
+      const int v = abs(out[k]) >> 2;
+      if (v) {
+        const int bin = (v > MAX_COEFF_THRESH) ? MAX_COEFF_THRESH : v;
+        histo[bin - 1]++;
+      }
+    }
+  }
+  return GetAlpha(histo);
+}
+
 //-----------------------------------------------------------------------------
 // run-time tables (~4k)
 
@@ -657,6 +699,7 @@ VP8CPUInfo VP8GetCPUInfo = NULL;
 
 // Speed-critical function pointers. We have to initialize them to the default
 // implementations within VP8EncDspInit().
+VP8CHisto VP8CollectHistogram;
 VP8Idct VP8ITransform;
 VP8Fdct VP8FTransform;
 VP8WHT VP8ITransformWHT;
@@ -681,6 +724,7 @@ void VP8EncDspInit(void) {
   InitTables();
 
   // default C implementations
+  VP8CollectHistogram = CollectHistogram;
   VP8ITransform = ITransform;
   VP8FTransform = FTransform;
   VP8ITransformWHT = ITransformWHT;

src/enc/dsp_sse2.c

@@ -18,6 +18,66 @@
 extern "C" {
 #endif
 
+//-----------------------------------------------------------------------------
+// Compute susceptibility based on DCT-coeff histograms:
+// the higher, the "easier" the macroblock is to compress.
+
+static int CollectHistogramSSE2(const uint8_t* ref, const uint8_t* pred,
+                                int start_block, int end_block) {
+  int histo[MAX_COEFF_THRESH + 1] = { 0 };
+  int16_t out[16];
+  int j, k;
+  const __m128i max_coeff_thresh = _mm_set1_epi16(MAX_COEFF_THRESH);
+  for (j = start_block; j < end_block; ++j) {
+    VP8FTransform(ref + VP8Scan[j], pred + VP8Scan[j], out);
+
+    // Convert coefficients to bin (within out[]).
+    {
+      // Load.
+      const __m128i out0 = _mm_loadu_si128((__m128i *)&out[0]);
+      const __m128i out1 = _mm_loadu_si128((__m128i *)&out[8]);
+      // sign(out) = out >> 15  (0x0000 if positive, 0xffff if negative)
+      const __m128i sign0 = _mm_srai_epi16(out0, 15);
+      const __m128i sign1 = _mm_srai_epi16(out1, 15);
+      // abs(out) = (out ^ sign) - sign
+      const __m128i xor0 = _mm_xor_si128(out0, sign0);
+      const __m128i xor1 = _mm_xor_si128(out1, sign1);
+      const __m128i abs0 = _mm_sub_epi16(xor0, sign0);
+      const __m128i abs1 = _mm_sub_epi16(xor1, sign1);
+      // v = abs(out) >> 2
+      const __m128i v0 = _mm_srai_epi16(abs0, 2);
+      const __m128i v1 = _mm_srai_epi16(abs1, 2);
+      // bin = min(v, MAX_COEFF_THRESH)
+      const __m128i bin0 = _mm_min_epi16(v0, max_coeff_thresh);
+      const __m128i bin1 = _mm_min_epi16(v1, max_coeff_thresh);
+      // Store.
+      _mm_storeu_si128((__m128i *)&out[0], bin0);
+      _mm_storeu_si128((__m128i *)&out[8], bin1);
+    }
+
+    // Use bin to update histogram.
+    for (k = 0; k < 16; ++k) {
+      histo[out[k]]++;
+    }
+  }
+
+  {
+    int num = 0, den = 0, val = 0;
+    int alpha;
+    for (k = 0; k < MAX_COEFF_THRESH; ++k) {
+      if (histo[k + 1]) {
+        val += histo[k + 1];
+        num += val * (k + 1);
+        den += (k + 1) * (k + 1);
+      }
+    }
+    // we scale the value to a usable [0..255] range
+    alpha = den ? 10 * num / den - 5 : 0;
+    alpha = alpha < 0 ? 0 : alpha > 255 ? 255 : alpha;
+    return alpha;
+  }
+}
+
 //-----------------------------------------------------------------------------
 // Transforms (Paragraph 14.4)
 
@@ -762,6 +822,7 @@ static int QuantizeBlockSSE2(int16_t in[16], int16_t out[16],
 
 extern void VP8EncDspInitSSE2(void);
 void VP8EncDspInitSSE2(void) {
+  VP8CollectHistogram = CollectHistogramSSE2;
   VP8EncQuantizeBlock = QuantizeBlockSSE2;
   VP8ITransform = ITransformSSE2;
   VP8FTransform = FTransformSSE2;

src/enc/vp8enci.h

@@ -28,6 +28,9 @@ extern "C" {
 #define ENC_MIN_VERSION 1
 #define ENC_REV_VERSION 2
 
+// size of histogram used by CollectHistogram.
+#define MAX_COEFF_THRESH   64
+
 // intra prediction modes
 enum { B_DC_PRED = 0,   // 4x4 modes
        B_TM_PRED = 1,
@@ -408,6 +411,11 @@ int VP8EncLoop(VP8Encoder* const enc);
 int VP8StatLoop(VP8Encoder* const enc);
 
   // in analysis.c
+// Compute susceptibility based on DCT-coeff histograms:
+// the higher, the "easier" the macroblock is to compress.
+typedef int (*VP8CHisto)(const uint8_t* ref, const uint8_t* pred,
+                         int start_block, int end_block);
+extern VP8CHisto VP8CollectHistogram;
 // Main analysis loop. Decides the segmentations and complexity.
 // Assigns a first guess for Intra16 and uvmode_ prediction modes.
 int VP8EncAnalyze(VP8Encoder* const enc);