Merge "introduce a generic GetCoeffs() function pointer"

src/dec/vp8.c

@@ -26,6 +26,16 @@ int WebPGetDecoderVersion(void) {
   return (DEC_MAJ_VERSION << 16) | (DEC_MIN_VERSION << 8) | DEC_REV_VERSION;
 }
 
+//------------------------------------------------------------------------------
+// Signature and pointer-to-function for GetCoeffs() variants below.
+
+typedef int (*GetCoeffsFunc)(VP8BitReader* const br,
+                             const VP8BandProbas* const prob[],
+                             int ctx, const quant_t dq, int n, int16_t* out);
+static volatile GetCoeffsFunc GetCoeffs = NULL;
+
+static void InitGetCoeffs(void);
+
 //------------------------------------------------------------------------------
 // VP8Decoder
 
@@ -51,6 +61,7 @@ VP8Decoder* VP8New(void) {
     WebPGetWorkerInterface()->Init(&dec->worker_);
     dec->ready_ = 0;
     dec->num_parts_minus_one_ = 0;
+    InitGetCoeffs();
   }
   return dec;
 }
@@ -422,8 +433,9 @@ static int GetLargeValue(VP8BitReader* const br, const uint8_t* const p) {
 }
 
 // Returns the position of the last non-zero coeff plus one
-static int GetCoeffs(VP8BitReader* const br, const VP8BandProbas* const prob[],
-                     int ctx, const quant_t dq, int n, int16_t* out) {
+static int GetCoeffsFast(VP8BitReader* const br,
+                         const VP8BandProbas* const prob[],
+                         int ctx, const quant_t dq, int n, int16_t* out) {
   const uint8_t* p = prob[n]->probas_[ctx];
   for (; n < 16; ++n) {
     if (!VP8GetBit(br, p[0])) {
@@ -449,6 +461,46 @@ static int GetCoeffs(VP8BitReader* const br, const VP8BandProbas* const prob[],
   return 16;
 }
 
+// This version of GetCoeffs() uses VP8GetBitAlt() which is an alternate version
+// of VP8GetBitAlt() targeting specific platforms.
+static int GetCoeffsAlt(VP8BitReader* const br,
+                        const VP8BandProbas* const prob[],
+                        int ctx, const quant_t dq, int n, int16_t* out) {
+  const uint8_t* p = prob[n]->probas_[ctx];
+  for (; n < 16; ++n) {
+    if (!VP8GetBitAlt(br, p[0])) {
+      return n;  // previous coeff was last non-zero coeff
+    }
+    while (!VP8GetBitAlt(br, p[1])) {       // sequence of zero coeffs
+      p = prob[++n]->probas_[0];
+      if (n == 16) return 16;
+    }
+    {        // non zero coeff
+      const VP8ProbaArray* const p_ctx = &prob[n + 1]->probas_[0];
+      int v;
+      if (!VP8GetBitAlt(br, p[2])) {
+        v = 1;
+        p = p_ctx[1];
+      } else {
+        v = GetLargeValue(br, p);
+        p = p_ctx[2];
+      }
+      out[kZigzag[n]] = VP8GetSigned(br, v) * dq[n > 0];
+    }
+  }
+  return 16;
+}
+
+WEBP_TSAN_IGNORE_FUNCTION static void InitGetCoeffs(void) {
+  if (GetCoeffs == NULL) {
+    if (VP8GetCPUInfo != NULL && VP8GetCPUInfo(kSlowSSSE3)) {
+      GetCoeffs = GetCoeffsAlt;
+    } else {
+      GetCoeffs = GetCoeffsFast;
+    }
+  }
+}
+
 static WEBP_INLINE uint32_t NzCodeBits(uint32_t nz_coeffs, int nz, int dc_nz) {
   nz_coeffs <<= 2;
   nz_coeffs |= (nz > 3) ? 3 : (nz > 1) ? 2 : dc_nz;

src/utils/bit_reader_inl.h

@@ -25,6 +25,7 @@
 #include "../dsp/dsp.h"
 #include "./bit_reader.h"
 #include "./endian_inl.h"
+#include "./utils.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -163,6 +164,37 @@ int VP8GetSigned(VP8BitReader* const br, int v) {
   }
 }
 
+static WEBP_INLINE int VP8GetBitAlt(VP8BitReader* const br, int prob) {
+  // Don't move this declaration! It makes a big speed difference to store
+  // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
+  // alter br->range_ value.
+  range_t range = br->range_;
+  if (br->bits_ < 0) {
+    VP8LoadNewBytes(br);
+  }
+  {
+    const int pos = br->bits_;
+    const range_t split = (range * prob) >> 8;
+    const range_t value = (range_t)(br->value_ >> pos);
+    int bit;  // Don't use 'const int bit = (value > split);", it's slower.
+    if (value > split) {
+      range -= split + 1;
+      br->value_ -= (bit_t)(split + 1) << pos;
+      bit = 1;
+    } else {
+      range = split;
+      bit = 0;
+    }
+    if (range <= (range_t)0x7e) {
+      const int shift = kVP8Log2Range[range];
+      range = kVP8NewRange[range];
+      br->bits_ -= shift;
+    }
+    br->range_ = range;
+    return bit;
+  }
+}
+
 #ifdef __cplusplus
 }    // extern "C"
 #endif