pitrou commented on code in PR #37460:
URL: https://github.com/apache/arrow/pull/37460#discussion_r1311607517
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cpp/src/arrow/io/buffered.cc:
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@@ -373,33 +378,42 @@ class BufferedInputStream::Impl : public BufferedBase {
return Status::Invalid("Bytes to read must be positive. Received:",
nbytes);
}
- if (nbytes < buffer_size_) {
- // Pre-buffer for small reads
- RETURN_NOT_OK(BufferIfNeeded());
+ // 1. First consume pre-buffered data.
+ int64_t pre_buffer_copy_bytes = std::min(nbytes, bytes_buffered_);
+ if (pre_buffer_copy_bytes > 0) {
+ memcpy(out, buffer_data_ + buffer_pos_, pre_buffer_copy_bytes);
+ ConsumeBuffer(pre_buffer_copy_bytes);
+ }
+ int64_t remaining_bytes = nbytes - pre_buffer_copy_bytes;
+ if (remaining_bytes == 0) {
+ return nbytes;
}
Review Comment:
This check can be removed if you rework the logic below a bit:
```c++
DCHECK_EQ(0, bytes_buffered_);
if (raw_read_bound_ >= 0) {
remaining_bytes = std::min(remaining_bytes, raw_read_bound_ -
raw_read_total_);
}
if (remaining_bytes == 0) {
return pre_buffer_copy_bytes;
}
```
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