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perf: hoist loop-invariant division out of reduce's cell loop #439

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perf: hoist loop-invariant division out of reduce's cell loop #439

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15 changes: 8 additions & 7 deletions include/boost/histogram/algorithm/reduce.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -405,6 +405,9 @@ Histogram reduce(const Histogram& hist, const Iterable& options) {
auto result =
Histogram(std::move(axes), detail::make_default(unsafe_access::storage(hist)));

for (auto& o : opts)
o.reduced_end = (o.end.index - o.begin.index) / static_cast<index_type>(o.merge);

auto idx = detail::make_stack_buffer<index_type>(unsafe_access::axes(result));
for (auto&& x : indexed(hist, coverage::all)) {
auto i = idx.begin();
Expand All @@ -417,14 +420,12 @@ Histogram reduce(const Histogram& hist, const Iterable& options) {
*i = -1;
if (!o->use_underflow_bin) skip = true;
} else {
if (*i >= 0)
if (*i < 0)
*i = o->reduced_end;
else if (o->merge > 1)
*i /= static_cast<index_type>(o->merge);
else
*i = o->end.index;
const auto reduced_axis_end =
(o->end.index - o->begin.index) / static_cast<index_type>(o->merge);
if (*i >= reduced_axis_end) {
*i = reduced_axis_end;
if (*i >= o->reduced_end) {
*i = o->reduced_end;
if (!o->use_overflow_bin) skip = true;
}
}
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1 change: 1 addition & 0 deletions include/boost/histogram/detail/reduce_command.hpp
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Expand Up @@ -33,6 +33,7 @@ struct reduce_command {
unsigned merge = 0; // default value indicates unset option
bool crop = false;
// for internal use by the reduce algorithm
axis::index_type reduced_end = 0; // (end - begin) / merge
bool is_ordered = true;
bool use_underflow_bin = true;
bool use_overflow_bin = true;
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