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staging: android: logger: simplify and optimize get_entry_len

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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@am.sony.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tim Bird 2012-02-08 10:37:57 -08:00 committed by Greg Kroah-Hartman
parent c626224de9
commit 3bcfa43133
1 changed files with 12 additions and 8 deletions
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20
drivers/staging/android/logger.c
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@ -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;
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];
else
((__u8 *)&val)[1] = log->buffer[0];
return sizeof(struct logger_entry) + val;
}