forked from M-Labs/nac3
65 lines
1.9 KiB
C++
65 lines
1.9 KiB
C++
#pragma once
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#include "irrt_utils.hpp"
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#include "irrt_typedefs.hpp"
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namespace {
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// A proper slice in IRRT, all negative indices have be resolved to absolute values.
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template <typename T>
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struct Slice {
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T start;
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T stop;
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T step;
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};
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template<typename T>
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T resolve_index_in_length(T length, T index) {
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nac3_assert(length >= 0);
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if (index < 0) {
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// Remember that index is negative, so do a plus here
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return max(length + index, 0);
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} else {
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return min(length, index);
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}
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}
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// NOTE: using a bitfield for the `*_defined` is better, at the
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// cost of a more annoying implementation in nac3core inkwell
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template <typename T>
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struct UserSlice {
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uint8_t start_defined;
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T start;
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uint8_t stop_defined;
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T stop;
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uint8_t step_defined;
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T step;
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// Like Python's `slice(start, stop, step).indices(length)`
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Slice<T> indices(T length) {
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// NOTE: This function implements Python's `slice.indices` *FAITHFULLY*.
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// SEE: https://github.com/python/cpython/blob/f62161837e68c1c77961435f1b954412dd5c2b65/Objects/sliceobject.c#L546
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nac3_assert(length >= 0);
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nac3_assert(!step_defined || step != 0); // step_defined -> step != 0; step cannot be zero if specified by user
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Slice<T> 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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if (start_defined) {
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result.start = resolve_index_in_length(length, start);
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} else {
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result.start = step_is_negative ? length - 1 : 0;
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}
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if (stop_defined) {
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result.stop = resolve_index_in_length(length, stop);
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} else {
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result.stop = step_is_negative ? -1 : length;
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}
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return result;
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}
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};
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} |