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core/irrt: add Slice and Range

Needed for implementing general ndarray indexing
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lyken 2024-08-20 12:33:31 +08:00
parent 5411ac5c88
commit bda003989e
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2 changed files with 202 additions and 1 deletions

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#include <irrt/ndarray/basic.hpp>
#include <irrt/ndarray/def.hpp>
#include <irrt/ndarray/iter.hpp>
#include <irrt/original.hpp>
#include <irrt/original.hpp>
#include <irrt/slice.hpp>

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