From 7f2da874cdacf2870c7a55cd1bdf34a01b01787d Mon Sep 17 00:00:00 2001 From: Laurent Pinchart Date: Sat, 29 Feb 2020 01:42:01 +0200 Subject: libcamera: byte_stream_buffer: Add zero-copy read() variant Add a read() function to ByteStreamBuffer that returns a pointer to the data instead of copying it. Overflow check is still handled by the class, but the caller must check the returned pointer explicitly. Signed-off-by: Laurent Pinchart Reviewed-by: Kieran Bingham --- src/libcamera/byte_stream_buffer.cpp | 39 ++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'src/libcamera/byte_stream_buffer.cpp') diff --git a/src/libcamera/byte_stream_buffer.cpp b/src/libcamera/byte_stream_buffer.cpp index 17e710c4..20d6a655 100644 --- a/src/libcamera/byte_stream_buffer.cpp +++ b/src/libcamera/byte_stream_buffer.cpp @@ -241,6 +241,19 @@ int ByteStreamBuffer::skip(size_t size) * \retval -ENOSPC no more space is available in the managed memory buffer */ +/** + * \fn template const T *ByteStreamBuffer::read(size_t count) + * \brief Read data from the managed memory buffer without performing a copy + * \param[in] count Number of data items to read + * + * This function reads \a count elements of type \a T from the buffer. Unlike + * the other read variants, it doesn't copy the data but returns a pointer to + * the first element. If data can't be read for any reason (usually due to + * reading more data than available), the function returns nullptr. + * + * \return A pointer to the data on success, or nullptr otherwise + */ + /** * \fn template int ByteStreamBuffer::write(const T *t) * \brief Write \a t to the managed memory buffer @@ -259,6 +272,32 @@ int ByteStreamBuffer::skip(size_t size) * \retval -ENOSPC no more space is available in the managed memory buffer */ +const uint8_t *ByteStreamBuffer::read(size_t size, size_t count) +{ + if (!read_) + return nullptr; + + if (overflow_) + return nullptr; + + size_t bytes; + if (__builtin_mul_overflow(size, count, &bytes)) { + setOverflow(); + return nullptr; + } + + if (read_ + bytes > base_ + size_) { + LOG(Serialization, Error) + << "Unable to read " << bytes << " bytes: out of bounds"; + setOverflow(); + return nullptr; + } + + const uint8_t *data = read_; + read_ += bytes; + return data; +} + int ByteStreamBuffer::read(uint8_t *data, size_t size) { if (!read_) -- cgit v1.2.1