On 2/8/2012 9:15 PM, Dima Zavin wrote:
On Wed, Feb 8, 2012 at 10:37 AM, Tim Bird<tim.bird@xxxxxxxxxxx> wrote:Make this code slightly easier to read, and eliminate calls to sub-routines. Some of these were previously optimized away by the compiler, but one memcpy was not. In my testing, this makes the code about 20% smaller, and has no sub-routine calls and no branches (on ARM). v2 of this patch is, IMHO, easier to read than v1. Compared to that patch it uses __u8 instead of unsigned char, for consistency with the __u16 val data type, simplifies the conditional expression, adds a another comment, and moves a common statement out of the if. Signed-off-by: Tim Bird<tim.bird@xxxxxxxxxxx> --- drivers/staging/android/logger.c | 20 ++++++++++++-------- 1 files changed, 12 insertions(+), 8 deletions(-) diff --git a/drivers/staging/android/logger.c b/drivers/staging/android/logger.c index 92456d7..3475cb7 100644 --- a/drivers/staging/android/logger.c +++ b/drivers/staging/android/logger.c @@ -93,20 +93,24 @@ static inline struct logger_log *file_get_log(struct file *file) * get_entry_len - Grabs the length of the payload of the next entry starting * from 'off'. * + * An entry length is 2 bytes (16 bits) in host endian order. + * In the log, the length does not include the size of the log entry structure. + * This function returns the size including the log entry structure. + * * Caller needs to hold log->mutex. */ static __u32 get_entry_len(struct logger_log *log, size_t off) { __u16 val;Could using a union here make things look a little cleaner in the meat of the function? Something like union { __u16 s; __u8 b[2]; } val;
That's a good idea. I was looking for a way to use a byte array that wouldn't get misaligned if the function declaration changed. I'll test this out and see what it looks like.
- switch (log->size - off) { - case 1: - memcpy(&val, log->buffer + off, 1); - memcpy(((char *)&val) + 1, log->buffer, 1); - break; - default: - memcpy(&val, log->buffer + off, 2); - } + /* copy 2 bytes from buffer, in memcpy order, */ + /* handling possible wrap at end of buffer */ + + ((__u8 *)&val)[0] = log->buffer[off]; + if (likely(off+1< log->size)) + ((__u8 *)&val)[1] = log->buffer[off+1];spaces around the + in 'off+1' in the above two lines.
Yeah. I keep omitting spaces. I'll fix this, and the ones mentioned on patch 1/5. -- Tim -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
