Convert the SSE2 delta decoder state into a class.

diff --git a/turbopfor.h b/turbopfor.h
index ef5c831ac376a948f3e9182be587fd31034908db..70b743832197bc5a0def98ffd67b087304c970ef 100644 (file)
--- a/turbopfor.h
+++ b/turbopfor.h
@@ -209,23 +209,34 @@ const unsigned char *decode_for(const unsigned char *in, unsigned num, Docid *ou
 }
 
 #ifdef COULD_HAVE_SSE2
+class DeltaDecoderSSE2 {
+public:
+       DeltaDecoderSSE2(uint32_t prev_val) : prev_val(_mm_set1_epi32(prev_val)) {}
+       __m128i decode(__m128i val) {
+               val = _mm_add_epi32(val, _mm_slli_si128(val, 4));
+               val = _mm_add_epi32(val, _mm_slli_si128(val, 8));
+               val = _mm_add_epi32(val, _mm_add_epi32(prev_val, delta));
+               prev_val = _mm_shuffle_epi32(val, _MM_SHUFFLE(3, 3, 3, 3));
+               return val;
+       }
+
+private:
+       // Use 4/3/2/1 as delta instead of fixed 1, so that we can do the prev_val + delta
+       // in parallel with something else.
+       const __m128i delta = _mm_set_epi32(4, 3, 2, 1);
+
+       __m128i prev_val;
+};
+
 template<unsigned BlockSize>
 __attribute__((target("sse2")))
 inline void delta_decode_sse2(uint32_t *out)
 {
-       // Use 4/3/2/1 as delta instead of fixed 1, so that we can do the prev_val + delta
-       // in parallel with something else.
-       const __m128i delta = _mm_set_epi32(4, 3, 2, 1);
-       __m128i prev_val = _mm_set1_epi32(out[-1]);
+       DeltaDecoderSSE2 delta(out[-1]);
        __m128i *outvec = reinterpret_cast<__m128i *>(out);
        for (unsigned i = 0; i < BlockSize / 4; ++i) {
                __m128i val = _mm_loadu_si128(outvec + i);
-               val = _mm_add_epi32(val, _mm_slli_si128(val, 4));
-               val = _mm_add_epi32(val, _mm_slli_si128(val, 8));
-               val = _mm_add_epi32(val, _mm_add_epi32(prev_val, delta));
-               _mm_storeu_si128(outvec + i, val);
-
-               prev_val = _mm_shuffle_epi32(val, _MM_SHUFFLE(3, 3, 3, 3));
+               _mm_storeu_si128(outvec + i, delta.decode(val));
        }
 }