Simplify reading of posting list header.

4 files changed, 35 insertions, 107 deletions

diff --git a/searchlib/src/vespa/searchlib/bitcompression/compression.h b/searchlib/src/vespa/searchlib/bitcompression/compression.h
index 33b5e0b0975..b9166f675aa 100644
--- a/searchlib/src/vespa/searchlib/bitcompression/compression.h
+++ b/searchlib/src/vespa/searchlib/bitcompression/compression.h
@@ -1141,7 +1141,7 @@ public:
     DecodeContext64Base()
         : search::ComprFileDecodeContext(),
           _valI(nullptr),
-          _valE(nullptr),
+          _valE(static_cast<const uint64_t *>(nullptr) - 1),
           _realValE(nullptr),
           _val(0),
           _cacheInt(0),
@@ -1298,6 +1298,8 @@ public:
         }
     }
     virtual uint64_t readBits(uint32_t length) = 0;
+    virtual void align(uint32_t alignment) = 0;
+    virtual uint64_t decode_exp_golomb(int k) = 0;
     void readBytes(uint8_t *buf, size_t len);
     uint32_t readHeader(vespalib::GenericHeader &header, int64_t fileSize);
 };
@@ -1321,7 +1323,7 @@ public:
     DecodeContext64(const uint64_t *compr,
                     int bitOffset)
         : DecodeContext64Base(compr + 1,
-                              nullptr,
+                              static_cast<const uint64_t *>(nullptr) - 1,
                               nullptr,
                               0,
                               EC::bswap(*compr),
@@ -1407,10 +1409,12 @@ public:
     };
 
     void skipBits(int bits) override {
+        readComprBufferIfNeeded();
         while (bits >= 64) {
             _val = 0;
             ReadBits(64, _val, _cacheInt, _preRead, _valI);
             bits -= 64;
+            readComprBufferIfNeeded();
         }
         if (bits > 0) {
             if (bigEndian) {
@@ -1419,6 +1423,7 @@ public:
                 _val >>= bits;
             }
             ReadBits(bits, _val, _cacheInt, _preRead, _valI);
+            readComprBufferIfNeeded();
         }
     }
 
@@ -1474,20 +1479,32 @@ public:
             _val = 0;
         }
         UC64_READBITS(_val, _valI, _preRead, _cacheInt, EC);
+        readComprBufferIfNeeded();
         return res;
     }
 
+    uint64_t decode_exp_golomb(int k) override {
+        uint32_t length;
+        uint64_t val64;
+        UC64_DECODEEXPGOLOMB(_val, _valI, _preRead, _cacheInt, k, EC);
+        readComprBufferIfNeeded();
+        return val64;
+    }
+
     void
-    align(uint32_t alignment)
+    align(uint32_t alignment) override
     {
+        readComprBufferIfNeeded();
         uint64_t pad = (- getReadOffset()) & (alignment - 1);
         while (pad > 64) {
             (void) readBits(64);
             pad -= 64;
+            readComprBufferIfNeeded();
         }
         if (pad > 0) {
             (void) readBits(pad);
         }
+        readComprBufferIfNeeded();
     }
 
     /*
@@ -1576,41 +1593,6 @@ public:
      */
     virtual void
     getParams(PostingListParams &params) const;
-
-    void skipBits(int bits) override {
-        readComprBufferIfNeeded();
-        while (bits >= 64) {
-            _val = 0;
-            ReadBits(64, _val, _cacheInt, _preRead, _valI);
-            bits -= 64;
-            readComprBufferIfNeeded();
-        }
-        if (bits > 0) {
-            if (bigEndian) {
-                _val <<= bits;
-            } else {
-                _val >>= bits;
-            }
-            ReadBits(bits, _val, _cacheInt, _preRead, _valI);
-            readComprBufferIfNeeded();
-        }
-    }
-
-    void
-    align(uint32_t alignment)
-    {
-        readComprBufferIfNeeded();
-        uint64_t pad = (- getReadOffset()) & (alignment - 1);
-        while (pad > 64) {
-            (void) readBits(64);
-            pad -= 64;
-            readComprBufferIfNeeded();
-        }
-        if (pad > 0) {
-            (void) readBits(pad);
-        }
-        readComprBufferIfNeeded();
-    }
 };
 
 typedef FeatureDecodeContext<true> FeatureDecodeContextBE;
diff --git a/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.cpp b/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.cpp
index 5288d054ef0..2149a44f5ce 100644
--- a/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.cpp
+++ b/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.cpp
@@ -20,35 +20,13 @@ Zc4PostingHeader::Zc4PostingHeader()
 {
 }
 
-template <bool bigEndian>
 void
 Zc4PostingHeader::read(bitcompression::DecodeContext64Base &decode_context, const Zc4PostingParams &params)
 {
-    using EC = bitcompression::FeatureEncodeContext<bigEndian>;
-    UC64_DECODECONTEXT_CONSTRUCTOR(o, decode_context._);
-    uint32_t length;
-    uint64_t val64;
-
-    UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_NUMDOCS, EC);
-    _num_docs = static_cast<uint32_t>(val64) + 1;
-    bool has_more = false;
-    if (__builtin_expect(_num_docs >= params._min_chunk_docs, false)) {
-        if (bigEndian) {
-            has_more = static_cast<int64_t>(oVal) < 0;
-            oVal <<= 1;
-            length = 1;
-        } else {
-            has_more = (oVal & 1) != 0;
-            oVal >>= 1;
-            length = 1;
-        }
-        UC64_READBITS_NS(o, EC);
-    }
-    if (params._dynamic_k) {
-        _doc_id_k = EC::calcDocIdK((_has_more || has_more) ? 1 : _num_docs, params._doc_id_limit);
-    } else {
-        _doc_id_k = K_VALUE_ZCPOSTING_LASTDOCID;
-    }
+    using EC = bitcompression::FeatureEncodeContext<true>;
+    _num_docs = decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_NUMDOCS) + 1;
+    bool has_more = (_num_docs >= params._min_chunk_docs) ? (decode_context.readBits(1) != 0) : false;
+    _doc_id_k = params._dynamic_k ? EC::calcDocIdK((_has_more || has_more) ? 1 : _num_docs, params._doc_id_limit) : K_VALUE_ZCPOSTING_LASTDOCID;
     if (_num_docs < params._min_skip_docs && !_has_more) {
         _doc_ids_size = 0;
         _l1_skip_size = 0;
@@ -58,47 +36,16 @@ Zc4PostingHeader::read(bitcompression::DecodeContext64Base &decode_context, cons
         _features_size = 0;
         _last_doc_id = 0;
     } else {
-        UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_DOCIDSSIZE, EC);
-        _doc_ids_size = val64 + 1;
-        UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_L1SKIPSIZE, EC);
-        _l1_skip_size = val64;
-        if (_l1_skip_size != 0) {
-            UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_L2SKIPSIZE, EC);
-            _l2_skip_size = val64;
-        }
-        if (_l2_skip_size != 0) {
-            UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_L3SKIPSIZE, EC);
-            _l3_skip_size = val64;
-        }
-        if (_l3_skip_size != 0) {
-            UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_L4SKIPSIZE, EC);
-            _l4_skip_size = val64;
-        }
-        if (params._encode_features) {
-            UC64_DECODEEXPGOLOMB_NS(o, K_VALUE_ZCPOSTING_FEATURESSIZE, EC);
-            _features_size = val64;
-        } else {
-            _features_size = 0;
-        }
-        UC64_DECODEEXPGOLOMB_NS(o, _doc_id_k, EC);
-        _last_doc_id = params._doc_id_limit - 1 - val64;
-        uint64_t bytePad = oPreRead & 7;
-        if (bytePad > 0) {
-            length = bytePad;
-            UC64_READBITS_NS(o, EC);
-        }
+        _doc_ids_size = decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_DOCIDSSIZE) + 1;
+        _l1_skip_size = decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_L1SKIPSIZE);
+        _l2_skip_size = (_l1_skip_size != 0) ? decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_L2SKIPSIZE) : 0;
+        _l3_skip_size = (_l2_skip_size != 0) ? decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_L3SKIPSIZE) : 0;
+        _l4_skip_size = (_l3_skip_size != 0) ? decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_L4SKIPSIZE) : 0;
+        _features_size = params._encode_features ? decode_context.decode_exp_golomb(K_VALUE_ZCPOSTING_FEATURESSIZE) : 0;
+        _last_doc_id = params._doc_id_limit - 1 - decode_context.decode_exp_golomb(_doc_id_k);
+        decode_context.align(8);
     }
-    UC64_DECODECONTEXT_STORE(o, decode_context._);
     _has_more = has_more;
 }
 
-template
-void
-Zc4PostingHeader::read<false>(bitcompression::DecodeContext64Base &decode_context, const Zc4PostingParams &params);
-
-template
-void
-Zc4PostingHeader::read<true>(bitcompression::DecodeContext64Base &decode_context, const Zc4PostingParams &params);
-
-
 }
diff --git a/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.h b/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.h
index 7382f59d176..d4032864e16 100644
--- a/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.h
+++ b/searchlib/src/vespa/searchlib/diskindex/zc4_posting_header.h
@@ -27,7 +27,6 @@ struct Zc4PostingHeader {
 
     Zc4PostingHeader();
 
-    template <bool bigEndian>
     void
     read(bitcompression::DecodeContext64Base &decode_context, const Zc4PostingParams &params);
 };
diff --git a/searchlib/src/vespa/searchlib/test/fakedata/fakezcfilterocc.cpp b/searchlib/src/vespa/searchlib/test/fakedata/fakezcfilterocc.cpp
index 25997faae24..f8fe31773c2 100644
--- a/searchlib/src/vespa/searchlib/test/fakedata/fakezcfilterocc.cpp
+++ b/searchlib/src/vespa/searchlib/test/fakedata/fakezcfilterocc.cpp
@@ -211,7 +211,7 @@ FakeZcFilterOcc::read_header(bool doFeatures, bool dynamicK, uint32_t min_skip_d
     decode_context.setPosition({ _compressed.first, 0 });
     Zc4PostingParams params(min_skip_docs, min_chunk_docs, _docIdLimit, dynamicK, doFeatures);
     Zc4PostingHeader header;
-    header.read<bigEndian>(decode_context, params);
+    header.read(decode_context, params);
     _docIdsSize = header._doc_ids_size;
     _l1SkipSize = header._l1_skip_size;
     _l2SkipSize = header._l2_skip_size;
@@ -429,7 +429,7 @@ FakeFilterOccZCArrayIterator::initRange(uint32_t begin, uint32_t end)
     DecodeContext &d = _decodeContext;
     Zc4PostingParams params(1, 1000000000, _docIdLimit, true, false);
     Zc4PostingHeader header;
-    header.read<true>(d, params);
+    header.read(d, params);
     assert((d.getBitOffset() & 7) == 0);
     const uint8_t *bcompr = d.getByteCompr();
     _valI = bcompr;
@@ -650,7 +650,7 @@ initRange(uint32_t begin, uint32_t end)
     DecodeContext &d = _decodeContext;
     Zc4PostingParams params(1, 1000000000, _docIdLimit, true, false);
     Zc4PostingHeader header;
-    header.read<true>(d, params);
+    header.read(d, params);
     _lastDocId = header._last_doc_id;
     assert((d.getBitOffset() & 7) == 0);
     const uint8_t *bcompr = d.getByteCompr();