forked from M-Labs/nac3
core/irrt: add Slice and Range
Needed for implementing general ndarray indexing
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#include <irrt/ndarray/basic.hpp>
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#include <irrt/ndarray/def.hpp>
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#include <irrt/ndarray/iter.hpp>
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#include <irrt/original.hpp>
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#include <irrt/original.hpp>
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#include <irrt/slice.hpp>
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200
nac3core/irrt/irrt/slice.hpp
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nac3core/irrt/irrt/slice.hpp
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#pragma once
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#include <irrt/debug.hpp>
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#include <irrt/exception.hpp>
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#include <irrt/int_types.hpp>
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#include <irrt/math_util.hpp>
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// The type of an index or a value describing the length of a
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// range/slice is always `int32_t`.
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using SliceIndex = int32_t;
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namespace
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{
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/**
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* @brief A Python range.
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*/
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struct Range
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{
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SliceIndex start;
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SliceIndex stop;
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SliceIndex step;
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/**
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* @brief Calculate the `len()` of this range.
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*/
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template <typename SizeT> SliceIndex len()
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{
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// Reference: https://github.com/python/cpython/blob/9dbd12375561a393eaec4b21ee4ac568a407cdb0/Objects/rangeobject.c#L933
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debug_assert(SizeT, step != 0);
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if (step > 0 && start < stop)
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return 1 + (stop - 1 - start) / step;
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else if (step < 0 && start > stop)
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return 1 + (start - 1 - stop) / (-step);
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else
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return 0;
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}
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};
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namespace slice
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{
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/**
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* @brief Resolve a slice index under a given length like Python indexing.
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*
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* In Python, if you have a `list` of length 100, `list[-1]` resolves to
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* `list[99]`, so `resolve_index_in_length_clamped(100, -1)` returns `99`.
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*
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* If `length` is 0, 0 is returned for any value of `index`.
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*
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* If `index` is out of bounds, clamps the returned value between `0` and
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* `length - 1` (inclusive).
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*
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*/
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SliceIndex resolve_index_in_length_clamped(SliceIndex length, SliceIndex index)
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{
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if (index < 0)
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{
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return max<SliceIndex>(length + index, 0);
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}
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else
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{
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return min<SliceIndex>(length, index);
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}
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}
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const SliceIndex OUT_OF_BOUNDS = -1;
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/**
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* @brief Like `resolve_index_in_length_clamped`, but returns `OUT_OF_BOUNDS`
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* if `index` is out of bounds.
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*/
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SliceIndex resolve_index_in_length(SliceIndex length, SliceIndex index)
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{
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SliceIndex resolved = index < 0 ? length + index : index;
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if (0 <= resolved && resolved < length)
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{
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return resolved;
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}
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else
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{
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return OUT_OF_BOUNDS;
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}
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}
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} // namespace slice
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/**
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* @brief A Python-like slice with **unresolved** indices.
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*/
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struct Slice
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{
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bool start_defined;
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SliceIndex start;
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bool stop_defined;
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SliceIndex stop;
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bool step_defined;
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SliceIndex step;
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Slice()
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{
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this->reset();
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}
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void reset()
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{
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this->start_defined = false;
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this->stop_defined = false;
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this->step_defined = false;
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}
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void set_start(SliceIndex start)
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{
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this->start_defined = true;
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this->start = start;
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}
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void set_stop(SliceIndex stop)
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{
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this->stop_defined = true;
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this->stop = stop;
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}
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void set_step(SliceIndex step)
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{
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this->step_defined = true;
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this->step = step;
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}
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/**
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* @brief Resolve this slice as a range.
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*
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* In Python, this would be `range(*slice(start, stop, step).indices(length))`.
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*/
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template <typename SizeT> Range indices(SliceIndex length)
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{
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// Reference: https://github.com/python/cpython/blob/main/Objects/sliceobject.c#L388
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debug_assert(SizeT, length >= 0);
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Range result;
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result.step = step_defined ? step : 1;
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bool step_is_negative = result.step < 0;
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SliceIndex lower, upper;
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if (step_is_negative)
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{
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lower = -1;
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upper = length - 1;
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}
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else
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{
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lower = 0;
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upper = length;
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}
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if (start_defined)
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{
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result.start = start < 0 ? max(lower, start + length) : min(upper, start);
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}
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else
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{
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result.start = step_is_negative ? upper : lower;
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}
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if (stop_defined)
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{
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result.stop = stop < 0 ? max(lower, stop + length) : min(upper, stop);
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}
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else
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{
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result.stop = step_is_negative ? lower : upper;
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}
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return result;
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}
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/**
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* @brief Like `.indices()` but with assertions.
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*/
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template <typename SizeT> Range indices_checked(SliceIndex length)
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{
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// TODO: Switch to `SizeT length`
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if (length < 0)
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{
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raise_exception(SizeT, EXN_VALUE_ERROR, "length should not be negative, got {0}", length, NO_PARAM,
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NO_PARAM);
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}
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if (this->step_defined && this->step == 0)
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{
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raise_exception(SizeT, EXN_VALUE_ERROR, "slice step cannot be zero", NO_PARAM, NO_PARAM, NO_PARAM);
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}
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return this->indices<SizeT>(length);
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}
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};
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} // namespace
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