Prepare for adjusting the genlod chunk size.

native/src/impl/genlod.cpp

@@ -403,7 +403,6 @@ GenLodImpl::_accumulate(const std::shared_ptr<const DataBuffer>& data)
  * enough and the decimation late enough that the chunk of data being
  * decimated has already been added to the histogram.
  *
- * TODO-@@@: if (_incremental) may want to reduce the block size.
  */
 std::shared_ptr<DataBuffer>
 GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_t readlod)
@@ -414,11 +413,21 @@ GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_
   const std::array<std::int64_t,3> readpos{readpos_in[0], readpos_in[1], 0};
   if (readpos[0] >= surveysize[0] || readpos[1] >= surveysize[1])
     return nullptr;
-  const std::array<std::int64_t,3> readsize
-    {std::min(2 * this->_bricksize[0], (surveysize[0] - readpos[0])),
-     std::min(2 * this->_bricksize[1], (surveysize[1] - readpos[1])),
+  // Amount of data to read. The method is allowed to return less,
+  // or even nothing, but only due to going past the survey edge.
+  // The choice is currently always the same so it is hard coded
+  // here instead of being passed as a parameter.
+  // TODO-@@@: if (_incremental) may want to reduce the block size.
+  const std::array<std::int64_t,3> chunksize
+    {this->_bricksize[0] * 2,
+     this->_bricksize[1] * 2,
      surveysize[2]}; // always read full traces.
-  const std::array<std::int64_t,3> writesize = (readsize + std::int64_t(1)) / std::int64_t(2);
+  const std::array<std::int64_t,3> readsize
+    {std::min(chunksize[0], (surveysize[0] - readpos[0])),
+     std::min(chunksize[1], (surveysize[1] - readpos[1])),
+     chunksize[2]};
+  // Size of the in-memory buffer of decimated data returned to the caller.
+  const std::array<std::int64_t,3> returnsize = (readsize + std::int64_t(1)) / std::int64_t(2);
 
   if (_verbose)
     std::cout << "@" << _prefix(readlod)
@@ -446,12 +455,11 @@ GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_
     wasread = true;
   }
   else {
-    const std::array<std::int64_t,3> bs = this->_bricksize;
     std::array<std::int64_t,3> offsets[4] =
-      {{    0,     0,   0},
-       {    0, bs[1],   0},
-       {bs[0],     0,   0},
-       {bs[0], bs[1],   0}};
+      {{           0,            0,   0},
+       {           0, chunksize[1],   0},
+       {chunksize[0],            0,   0},
+       {chunksize[0], chunksize[1],   0}};
     std::shared_ptr<DataBuffer> hires[4]{nullptr, nullptr, nullptr, nullptr};
 
     // TODO-Performance: If algorithm "C" and readlod==1 it should be
@@ -473,7 +481,7 @@ GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_
     // Also, carefully analyze how this affects total memory usage.
 
     for (int ii=0; ii<4; ++ii)
-      hires[ii] = this->_calculate(readpos*std::int64_t(2) + offsets[ii]*std::int64_t(2), readlod-1);
+      hires[ii] = this->_calculate(readpos*std::int64_t(2) + offsets[ii], readlod-1);
     data = this->_paste4(hires[0], hires[1], hires[2], hires[3]);
   }
 
@@ -500,7 +508,7 @@ GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_
   }
   else if (data->isScalar()) {
     result = DataBuffer::makeScalarBuffer3d
-      (data->scalarAsDouble(), writesize, data->datatype());
+      (data->scalarAsDouble(), returnsize, data->datatype());
   }
   else {
     // TODO-Performance: Enable parallelization (in genlod.cpp) of this call.
@@ -509,14 +517,19 @@ GenLodImpl::_calculate(const std::array<std::int64_t,3>& readpos_in, std::int32_
     // parallelize this low level loop. // omp_set_nested(1) or better, use
     // omp_set_max_active_levels(...).
     result = this->_decimate(data, readlod+1);
-    if (result->size3d() != writesize)
-      throw OpenZGY::Errors::ZgyInternalError("GenLodImpl: Wrong writesize.");
+    if (result->size3d() != returnsize) {
+      std::cout << "Decimation returned " << result->size3d()
+                << ", expected " << returnsize
+                << ", start " << readpos
+                << ", size=" << readsize << "\n";
+      throw OpenZGY::Errors::ZgyInternalError("GenLodImpl: Wrong returnsize.");
+    }
   }
   if (this->_verbose)
     std::cout << "@" << _prefix(readlod)
               << "calculate returns(lod="
               << readlod+1 << ", pos=" << readpos << " / 2"
-              << ", size=" << writesize
+              << ", size=" << returnsize
               << ", data=" << data->toString() << ")\n";
   return result;
 }