## Coverage Report

#### Created: 2025-08-26 07:03

next uncovered line (L), next uncovered region (R), next uncovered branch (B)

    /Users/andrewlamb/Software/arrow-rs/arrow-data/src/transform/utils.rs

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    // Licensed to the Apache Software Foundation (ASF) under one
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    // or more contributor license agreements.  See the NOTICE file
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    // distributed with this work for additional information
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    // regarding copyright ownership.  The ASF licenses this file
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    // to you under the Apache License, Version 2.0 (the
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    // "License"); you may not use this file except in compliance
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    // with the License.  You may obtain a copy of the License at
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    //
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    //   http://www.apache.org/licenses/LICENSE-2.0
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    //
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    // Unless required by applicable law or agreed to in writing,
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    // software distributed under the License is distributed on an
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    // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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    // KIND, either express or implied.  See the License for the
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    // specific language governing permissions and limitations
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    // under the License.
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    use arrow_buffer::{bit_util, ArrowNativeType, MutableBuffer};
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    use num::{CheckedAdd, Integer};
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    /// extends the `buffer` to be able to hold `len` bits, setting all bits of the new size to zero.
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    #[inline]
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    pub(super) fn resize_for_bits(buffer: &mut MutableBuffer, len: usize) {
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        let needed_bytes = bit_util::ceil(len, 8);
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        if buffer.len() < needed_bytes {
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            buffer.resize(needed_bytes, 0);
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        }
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    }
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    pub(super) fn extend_offsets<T: ArrowNativeType + Integer + CheckedAdd>(
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        buffer: &mut MutableBuffer,
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        mut last_offset: T,
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        offsets: &[T],
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    ) {
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        buffer.reserve(std::mem::size_of_val(offsets));
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        offsets21.windows21(2).for_each21(|offsets| {
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            // compute the new offset
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            let length = offsets[1] - offsets[0];
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            // if you hit this appending to a StringArray / BinaryArray it is because you
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            // are trying to add more data than can fit into that type. Try breaking your data into
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            // smaller batches or using LargeStringArray / LargeBinaryArray
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            last_offset = last_offset.checked_add(&length).expect("offset overflow");
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            buffer.push(last_offset);
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        });
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    }
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    #[inline]
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    pub(super) unsafe fn get_last_offset<T: ArrowNativeType>(offset_buffer: &MutableBuffer) -> T {
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        // JUSTIFICATION
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        //  Benefit
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        //      20% performance improvement extend of variable sized arrays (see bench `mutable_array`)
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        //  Soundness
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        //      * offset buffer is always extended in slices of T and aligned accordingly.
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        //      * Buffer[0] is initialized with one element, 0, and thus `mutable_offsets.len() - 1` is always valid.
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        let (prefix, offsets, suffix) = offset_buffer.as_slice().align_to::<T>();
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        debug_assert!(prefix.is_empty() && suffix.is_empty());
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        *offsets.get_unchecked(offsets.len() - 1)
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    }
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    #[cfg(test)]
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    mod tests {
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        use crate::transform::utils::extend_offsets;
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        use arrow_buffer::MutableBuffer;
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        #[test]
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        #[should_panic(expected = "offset overflow")]
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        fn test_overflow() {
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            let mut buffer = MutableBuffer::new(10);
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            extend_offsets(&mut buffer, i32::MAX - 4, &[0, 5]);
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        }
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    }