Speed up delta-decoding, giving us 50% (!) speed boost and taking us to 30% of refere...

diff --git a/turbopfor.h b/turbopfor.h
index 12150f9485aee882b561290beb5642594b0be1c0..51ee66ea65bc8defe56ee2b53ad2799859db2f2a 100644 (file)
--- a/turbopfor.h
+++ b/turbopfor.h
@@ -160,9 +160,9 @@ const unsigned char *decode_constant(const unsigned char *in, unsigned num, Doci
                val &= ((1U << bit_width) - 1);
        }
 
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        for (unsigned i = 0; i < num; ++i) {
-               out[i] = val + prev_out[i] + 1;
+               out[i] = prev_val = val + prev_val + 1;
        }
        return in + div_round_up(bit_width, 8);
 }
@@ -176,10 +176,10 @@ const unsigned char *decode_for(const unsigned char *in, unsigned num, Docid *ou
 {
        const unsigned bit_width = *in++ & 0x3f;
 
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        BitReader bs(in, bit_width);
        for (unsigned i = 0; i < num; ++i) {
-               out[i] = bs.read() + prev_out[i] + 1;
+               prev_val = out[i] = bs.read() + prev_val + 1;
        }
        return in + bytes_for_packed_bits(num, bit_width);
 }
@@ -201,9 +201,9 @@ const unsigned char *decode_for_interleaved(const unsigned char *in, Docid *out)
                out[i * 4 + 2] = bs2.read();
                out[i * 4 + 3] = bs3.read();
        }
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        for (unsigned i = 0; i < BlockSize; ++i) {
-               out[i] += prev_out[i] + 1;
+               out[i] = prev_val = out[i] + prev_val + 1;
        }
        return in + bytes_for_packed_bits(BlockSize, bit_width);
 }
@@ -246,10 +246,10 @@ const unsigned char *decode_pfor_bitmap(const unsigned char *in, unsigned num, D
        }
 
        // Decode the base values, and delta-decode.
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        BitReader bs(in, bit_width);
        for (unsigned i = 0; i < num; ++i) {
-               out[i] = (out[i] | bs.read()) + prev_out[i] + 1;
+               out[i] = prev_val = (out[i] | bs.read()) + prev_val + 1;
        }
        return in + bytes_for_packed_bits(num, bit_width);
 }
@@ -293,9 +293,9 @@ const unsigned char *decode_pfor_bitmap_interleaved(const unsigned char *in, Doc
                out[i * 4 + 2] |= bs2.read();
                out[i * 4 + 3] |= bs3.read();
        }
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        for (unsigned i = 0; i < BlockSize; ++i) {
-               out[i] += prev_out[i] + 1;
+               out[i] = prev_val = out[i] + prev_val + 1;
        }
        return in + bytes_for_packed_bits(BlockSize, bit_width);
 }
@@ -344,9 +344,9 @@ const unsigned char *decode_pfor_vb(const unsigned char *in, unsigned num, Docid
        }
 
        // Delta-decode.
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        for (unsigned i = 0; i < num; ++i) {
-               out[i] = out[i] + prev_out[i] + 1;
+               out[i] = prev_val = out[i] + prev_val + 1;
        }
 
        return in;
@@ -394,9 +394,9 @@ const unsigned char *decode_pfor_vb_interleaved(const unsigned char *in, Docid *
        }
 
        // Delta-decode.
-       Docid *prev_out = out - 1;
+       Docid prev_val = out[-1];
        for (unsigned i = 0; i < BlockSize; ++i) {
-               out[i] = out[i] + prev_out[i] + 1;
+               out[i] = prev_val = out[i] + prev_val + 1;
        }
 
        return in;