pitrou commented on code in PR #50217:
URL: https://github.com/apache/arrow/pull/50217#discussion_r3452895999
##########
cpp/src/arrow/util/bit_util.h:
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@@ -176,6 +179,54 @@ static constexpr bool GetBitFromByte(uint8_t byte, uint8_t
i) {
return byte & kBitmask[i];
}
+/// Read 32 bits starting at bit `offset` into a uint32.
+///
+/// The return value in in-memory byte layout matches the source bit-stream
+/// identically on little- and big-endian platforms.
+///
+/// The caller must guarantee that many bytes are readable.
+static inline uint32_t Get32Bits(const uint8_t* bits, uint64_t offset) {
+ uint64_t buffer = {};
+ std::memcpy(&buffer, bits + (offset / 8), BytesForBits(offset % 8 + 32));
+ // Interpret the loaded bytes as little-endian, drop the low `offset % 8`
bits
+ // to align LSB-first, then store back in little-endian byte order so the
+ // result's memory representation matches the bit-stream.
+ buffer = FromLittleEndian(buffer);
+ return ToLittleEndian(static_cast<uint32_t>(buffer >> (offset % 8)));
+}
+
+template <typename Uint>
+struct CopyBitsParams {
+ Uint src = {};
+ Uint dst = {};
+ Uint start = {};
+ Uint end = {};
Review Comment:
Not sure why `start` and `end` are templated as well?
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