forked from M-Labs/nac3
83 lines
2.8 KiB
C++
83 lines
2.8 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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struct Slice {
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SliceIndex start;
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SliceIndex stop;
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SliceIndex step;
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// The length/The number of elements of the slice if it were a range,
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// i.e., the value of `len(range(this->start, this->stop, this->end))`
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SliceIndex len() {
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SliceIndex diff = stop - start;
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if (diff > 0 && step > 0) {
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return ((diff - 1) / step) + 1;
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} else if (diff < 0 && step < 0) {
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return ((diff + 1) / step) + 1;
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} else {
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return 0;
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}
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}
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};
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SliceIndex resolve_index_in_length(SliceIndex length, SliceIndex index) {
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irrt_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<SliceIndex>(length + index, 0);
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} else {
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return min<SliceIndex>(length, index);
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}
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}
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// A user-written Python-like slice.
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//
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// i.e., this slice is a triple of either an int or nothing. (e.g., `my_array[:10:2]`, `start` is None)
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//
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// You can "resolve" a `UserSlice` by using `UserSlice::indices(<length>)`
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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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struct UserSlice {
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// Did the user specify `start`? If 0, `start` is undefined (and contains an empty value)
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uint8_t start_defined;
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SliceIndex start;
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// Similar to `start_defined`
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uint8_t stop_defined;
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SliceIndex stop;
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// Similar to `start_defined`
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uint8_t step_defined;
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SliceIndex step;
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// Like Python's `slice(start, stop, step).indices(length)`
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Slice indices(SliceIndex 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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irrt_assert(length >= 0);
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irrt_assert(!step_defined || step != 0); // step_defined -> step != 0; step cannot be zero if specified by user
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Slice 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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} |