rescaler: move the 1x1 or 2x1 handling one level up

=> no need to handle it in the sub-functions.

Change-Id: I4b0211ecfafbc9c80a73bf2206809a13c94e7911

src/dsp/rescaler.c

@@ -140,18 +140,13 @@ void WebPRescalerExportRowShrinkC(WebPRescaler* const wrk) {
       dst[x_out] = v;
       irow[x_out] = frac;   // new fractional start
     }
-  } else if (wrk->fxy_scale) {
+  } else {
     for (x_out = 0; x_out < x_out_max; ++x_out) {
       const int v = (int)MULT_FIX(irow[x_out], wrk->fxy_scale);
       assert(v >= 0 && v <= 255);
       dst[x_out] = v;
       irow[x_out] = 0;
     }
-  } else {  // very special case for src = dst = 1x1
-    for (x_out = 0; x_out < x_out_max; ++x_out) {
-      dst[x_out] = irow[x_out];
-      irow[x_out] = 0;
-    }
   }
 }
 
@@ -175,8 +170,16 @@ void WebPRescalerExportRow(WebPRescaler* const wrk) {
     assert(!WebPRescalerOutputDone(wrk));
     if (wrk->y_expand) {
       WebPRescalerExportRowExpand(wrk);
-    } else {
+    } else if (wrk->fxy_scale) {
       WebPRescalerExportRowShrink(wrk);
+    } else {  // very special case for src = dst = 1x1
+      int i;
+      assert(wrk->src_width == 1 && wrk->dst_width <= 2);
+      assert(wrk->src_height == 1 && wrk->dst_height == 1);
+      for (i = 0; i < wrk->num_channels * wrk->dst_width; ++i) {
+        wrk->dst[i] = wrk->irow[i];
+        wrk->irow[i] = 0;
+      }
     }
     wrk->y_accum += wrk->y_add;
     wrk->dst += wrk->dst_stride;

src/dsp/rescaler_mips32.c

@@ -141,16 +141,16 @@ static void ExportRowShrink(WebPRescaler* const wrk) {
   const int x_out_max = wrk->dst_width * wrk->num_channels;
   uint8_t* dst = wrk->dst;
   rescaler_t* irow = wrk->irow;
-  assert(!WebPRescalerOutputDone(wrk));
-  assert(wrk->y_accum <= 0);
-  assert(!wrk->y_expand);
-  if (wrk->fxy_scale != 0) {
   const rescaler_t* frow = wrk->frow;
   const int yscale = wrk->fy_scale * (-wrk->y_accum);
   int temp0, temp1, temp3, temp4, temp5, temp6, temp7, loop_end;
-    const int temp2 = (int)(wrk->fxy_scale);
+  const int temp2 = (int)wrk->fxy_scale;
   const int temp8 = x_out_max << 2;
 
+  assert(!WebPRescalerOutputDone(wrk));
+  assert(wrk->y_accum <= 0);
+  assert(!wrk->y_expand);
+  assert(wrk->fxy_scale != 0);
   __asm__ volatile(
     "addiu    %[temp6],    $zero,       -256          \n\t"
     "addiu    %[temp7],    $zero,       255           \n\t"
@@ -189,13 +189,6 @@ static void ExportRowShrink(WebPRescaler* const wrk) {
     : [temp2]"r"(temp2), [yscale]"r"(yscale), [temp8]"r"(temp8)
     : "memory", "hi", "lo"
   );
-  } else {  // very special case for src = dst = 1x1
-    int x_out;
-    for (x_out = 0; x_out < x_out_max; ++x_out) {
-      dst[x_out] = irow[x_out];
-      irow[x_out] = 0;
-    }
-  }
 }
 
 // no ExportRowExpand yet.

src/dsp/rescaler_mips_dsp_r2.c

@@ -136,10 +136,6 @@ static void ExportRowShrink(WebPRescaler* const wrk) {
   uint8_t* dst = wrk->dst;
   rescaler_t* irow = wrk->irow;
   const int x_out_max = wrk->dst_width * wrk->num_channels;
-  assert(!WebPRescalerOutputDone(wrk));
-  assert(wrk->y_accum <= 0);
-  assert(!wrk->y_expand);
-  if (wrk->fxy_scale) {
   const rescaler_t* frow = wrk->frow;
   const int yscale = wrk->fy_scale * (-wrk->y_accum);
 
@@ -148,6 +144,10 @@ static void ExportRowShrink(WebPRescaler* const wrk) {
   const int rest = x_out_max & 1;
   const rescaler_t* const loop_end = frow + x_out_max - rest;
 
+  assert(!WebPRescalerOutputDone(wrk));
+  assert(wrk->y_accum <= 0);
+  assert(!wrk->y_expand);
+  assert(wrk->fxy_scale);
   __asm__ volatile (
       ".set             push                                    \n\t"
       ".set             noreorder                               \n\t"
@@ -210,13 +210,6 @@ static void ExportRowShrink(WebPRescaler* const wrk) {
       [rest]"r"(rest)
     : "memory", "hi", "lo"
   );
-  } else {  // very special case for src = dst = 1x1
-    int x_out;
-    for (x_out = 0; x_out < x_out_max; ++x_out) {
-      dst[x_out] = irow[x_out];
-      irow[x_out] = 0;
-    }
-  }
 }
 
 // no ExportRowExpand yet.

src/dsp/rescaler_sse2.c

@@ -187,7 +187,7 @@ static void RescalerExportRowShrinkSSE2(WebPRescaler* const wrk) {
       dst[x_out] = v;
       irow[x_out] = frac;   // new fractional start
     }
-  } else if (wrk->fxy_scale) {
+  } else {
     const uint32_t scale = wrk->fxy_scale;
     const __m128i mult = _mm_set_epi32(0, scale, 0, scale);
     const __m128i zero = _mm_setzero_si128();
@@ -204,11 +204,6 @@ static void RescalerExportRowShrinkSSE2(WebPRescaler* const wrk) {
       dst[x_out] = v;
       irow[x_out] = 0;
     }
-  } else {  // very special case for src = 1x1
-    for (x_out = 0; x_out < x_out_max; ++x_out) {
-      dst[x_out] = irow[x_out];
-      irow[x_out] = 0;
-    }
   }
 }
 

src/utils/rescaler.c

@@ -49,7 +49,7 @@ void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
   wrk->y_accum = wrk->y_expand ? wrk->y_sub : wrk->y_add;
   if (!wrk->y_expand) {
     // note the very special case where x_add = y_add = 1 cannot be represented.
-    // We special-case fxy_scale = 0 in this case, in ExportRowShrink
+    // We special-case fxy_scale = 0 in this case, in WebPRescalerExportRow().
     wrk->fxy_scale = WEBP_RESCALER_FRAC(dst_height, wrk->x_add * wrk->y_add);
     wrk->fy_scale = WEBP_RESCALER_FRAC(1, wrk->y_sub);
   } else {