SSE2: resize filter to 7x7. clean up a little.

blur_simd.c

@@ -14,7 +14,7 @@
 #include <immintrin.h>
 
 #define ALIGN16 __attribute__((aligned(16)))
-#define KERNEL_SIZE 15 
+#define KERNEL_SIZE 7 
 #define HALF_KERNEL KERNEL_SIZE / 2
 
 // number of xmm registers needed to store 
@@ -90,30 +90,25 @@ void blur_impl_horizontal_pass_sse2(uint32_t *src, uint32_t *dst, float *kernel,
                     rgbaIn[k] = _mm_loadu_si128((__m128i*)(src + 4*k - HALF_KERNEL));
             }
 
-            __m128i tmp;
             __m128i zero = _mm_setzero_si128();
             __m128i acc = _mm_setzero_si128();
 
-            for (int i = 0; i < 3; i++)
-            {
-                acc = _mm_add_epi16(acc, _mm_unpacklo_epi8(rgbaIn[i], zero));
-                acc = _mm_add_epi16(acc, _mm_unpackhi_epi8(rgbaIn[i], zero));
-            }
-
-            acc = _mm_add_epi16(acc, _mm_unpacklo_epi8(rgbaIn[3], zero));
+            acc = _mm_add_epi16(acc, _mm_unpacklo_epi8(rgbaIn[0], zero));
+            acc = _mm_add_epi16(acc, _mm_unpackhi_epi8(rgbaIn[0], zero));
+            acc = _mm_add_epi16(acc, _mm_unpacklo_epi8(rgbaIn[1], zero));
 
-            tmp = _mm_unpackhi_epi8(rgbaIn[3], zero);
-            // set 16th pixel to zeroes
-            tmp = _mm_andnot_si128(_mm_set_epi16(0xFFFF, 0xFFFF, 0xFFFF, 0xFFFF, 0,0,0,0), tmp);
-            acc = _mm_add_epi16(acc, tmp);
-            acc = _mm_add_epi32(_mm_unpacklo_epi16(acc, zero), _mm_unpackhi_epi16(acc, zero));
+            // kernel size equals to 7, but we can only load multiples of 4 pixels
+            // we have to set 8th pixel to zero
+            acc = _mm_add_epi16(acc, _mm_andnot_si128(_mm_set_epi32(0xFFFFFFFF, 0xFFFFFFFF, 0, 0), 
+                                                      _mm_unpackhi_epi8(rgbaIn[1], zero)));
+            acc = _mm_add_epi32(_mm_unpacklo_epi16(acc, zero), 
+                                _mm_unpackhi_epi16(acc, zero));
 
             acc = _mm_cvtps_epi32(_mm_mul_ps(_mm_cvtepi32_ps(acc),
-                                             _mm_set1_ps(1/((float)(KERNEL_SIZE)))));
+                                             _mm_set1_ps(1/((float)KERNEL_SIZE))));
 
-            acc = _mm_packs_epi32(acc, zero);
-            acc = _mm_packus_epi16(acc, zero);
-            *(dst + height * column + row) = _mm_cvtsi128_si32(acc);
+            *(dst + height * column + row) = 
+                _mm_cvtsi128_si32(_mm_packus_epi16(_mm_packs_epi32(acc, zero), zero));
         }
     }
 }