pitrou commented on code in PR #39245:
URL: https://github.com/apache/arrow/pull/39245#discussion_r1434334074
##########
cpp/src/arrow/compute/kernels/scalar_string_test.cc:
##########
@@ -712,6 +712,95 @@ TEST_F(TestFixedSizeBinaryKernels, BinaryLength) {
"[6, null, 6]");
}
+TEST_F(TestFixedSizeBinaryKernels, SliceBytesBasic) {
+ SliceOptions options{2, 4};
+ CheckUnary("binary_slice", R"(["abcabc", "defdef"])", fixed_size_binary(2),
Review Comment:
Can we use less repeated values to make sure the substring selection is
right?
```suggestion
CheckUnary("binary_slice", R"(["abcdef", "ghijkl"])", fixed_size_binary(2),
```
##########
cpp/src/arrow/compute/kernels/scalar_string_test.cc:
##########
@@ -712,6 +712,95 @@ TEST_F(TestFixedSizeBinaryKernels, BinaryLength) {
"[6, null, 6]");
}
+TEST_F(TestFixedSizeBinaryKernels, SliceBytesBasic) {
Review Comment:
Nit
```suggestion
TEST_F(TestFixedSizeBinaryKernels, BinarySliceBasic) {
```
##########
cpp/src/arrow/compute/kernels/scalar_string_test.cc:
##########
@@ -712,6 +712,95 @@ TEST_F(TestFixedSizeBinaryKernels, BinaryLength) {
"[6, null, 6]");
}
+TEST_F(TestFixedSizeBinaryKernels, SliceBytesBasic) {
+ SliceOptions options{2, 4};
+ CheckUnary("binary_slice", R"(["abcabc", "defdef"])", fixed_size_binary(2),
Review Comment:
Also, can you add some null values at some point?
##########
cpp/src/arrow/compute/kernels/scalar_string_ascii.cc:
##########
@@ -2568,6 +2571,32 @@ struct SliceBytesTransform : StringSliceTransformBase {
return dest - output;
}
+
+ static Result<int32_t> FixedOutputSize(SliceOptions options, int32_t
input_width_32) {
+ auto step = options.step;
+ if (step == 0) {
+ return Status::Invalid("Slice step cannot be zero");
+ }
+ auto start = options.start;
+ auto stop = options.stop;
+ auto input_width = static_cast<int64_t>(input_width_32);
+
+ if (start < 0) {
+ start = std::max(static_cast<int64_t>(0), start + input_width);
+ }
+ if (stop < 0) {
+ stop = std::max(static_cast<int64_t>(0), stop + input_width);
+ }
+ start = std::min(start, input_width);
+ stop = std::min(stop, input_width);
+
+ if ((start == stop) || ((start >= stop) && (step > 0)) ||
+ ((start <= stop) && (step < 0))) {
+ return 0;
+ }
+ return static_cast<int32_t>(std::max(
+ static_cast<int64_t>(0), (stop - start + (step - (step > 0 ? 1 : -1)))
/ step));
+ }
Review Comment:
Hmm, can you rephrase the code such that `step > 0` and `step < 0` have
separate code paths? It would make things clearer.
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