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Array: Relax slice bound checks to properly handle negative indices

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The same is done for `Vector` (and thus `Packed*Array`).

`begin` and `end` can now take any value and will be clamped to
`[-size(), size()]`. Negative values are a shorthand for indexing the array
from the last element upward.

`end` is given a default `INT_MAX` value (which will be clamped to `size()`)
so that the `end` parameter can be omitted to go from `begin` to the max size
of the array.

This makes `slice` works similarly to numpy's and JavaScript's.
This commit is contained in:
Rémi Verschelde
2022-01-10 13:56:55 +01:00
parent 4acc819f9b
commit c6cefb1b79
16 changed files with 129 additions and 52 deletions
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22
core/variant/array.cpp
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@@ -370,20 +370,24 @@ Array Array::slice(int p_begin, int p_end, int p_step, bool p_deep) const {
ERR_FAIL_COND_V_MSG(p_step == 0, result, "Slice step cannot be zero.");
if (p_end < 0) {
p_end += size() + 1;
const int s = size();
int begin = CLAMP(p_begin, -s, s);
if (begin < 0) {
begin += s;
}
int end = CLAMP(p_end, -s, s);
if (end < 0) {
end += s;
}
ERR_FAIL_INDEX_V(p_begin, size(), result);
ERR_FAIL_INDEX_V(p_end, size() + 1, result);
ERR_FAIL_COND_V_MSG(p_step > 0 && begin > end, result, "Slice is positive, but bounds is decreasing.");
ERR_FAIL_COND_V_MSG(p_step < 0 && begin < end, result, "Slice is negative, but bounds is increasing.");
ERR_FAIL_COND_V_MSG(p_step > 0 && p_begin > p_end, result, "Slice is positive, but bounds is decreasing");
ERR_FAIL_COND_V_MSG(p_step < 0 && p_begin < p_end, result, "Slice is negative, but bounds is increasing");
int result_size = (p_end - p_begin) / p_step;
int result_size = (end - begin) / p_step;
result.resize(result_size);
for (int src_idx = p_begin, dest_idx = 0; dest_idx < result_size; ++dest_idx) {
for (int src_idx = begin, dest_idx = 0; dest_idx < result_size; ++dest_idx) {
result[dest_idx] = p_deep ? get(src_idx).duplicate(true) : get(src_idx);
src_idx += p_step;
}