Commit 9fb4ab4d authored Dec 20, 2018 by Andrey Smirnov Committed by Greg Kroah-Hartman Jan 22, 2019

ihex: Simplify next record offset calculation



Next record calucaltion can be reduced to a much more tivial ALIGN
operation as follows:

1. Splitting 5 into 2 + 3 we get

   next = ((be16_to_cpu(rec->len) + 2 + 3) & ~3) - 2            (1)

2. Using ALIGN macro we reduce (1) to:

   ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2                      (2)

3. Subsituting 'next' in original next record calucation we get:

   (void *)&rec->data[ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2]  (3)

4. Converting array index to pointer arithmetic we convert (3) into:

   (void *)rec + sizeof(*rec) +
   	 ALIGN(be16_to_cpu(rec->len) + 2, 4) - 2		(4)

5. Subsituting sizeof(*rec) with its value, 6, and substracting 2,
   in (4) we get:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + 2, 4) + 4        (5)

6. Since ALIGN(X, 4) + 4 == ALIGN(X + 4, 4), (5) can be converted to:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + 6, 4)            (6)

5. Subsituting 6 in (6) to sizeof(*rec) we get:

   (void *)rec + ALIGN(be16_to_cpu(rec->len) + sizeof(*rec), 4) (7)

Using expression (7) should make it more clear that next record is
located by adding full size of the current record (payload + auxiliary
data) aligned to 4 bytes, to the location of the current one. No
functional change intended.

Cc: Chris Healy <cphealy@gmail.com>
Cc: Kyle McMartin <kyle@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 5158c36e

include/linux/ihex.h

+7 −3

Original line number	Diff line number	Diff line
		@@ -21,14 +21,18 @@ struct ihex_binrec {
		uint8_t data[0];
		} __attribute__((packed));

		static inline uint16_t ihex_binrec_size(const struct ihex_binrec *p)
		{
		return be16_to_cpu(p->len) + sizeof(*p);
		}

		/* Find the next record, taking into account the 4-byte alignment */
		static inline const struct ihex_binrec *
		__ihex_next_binrec(const struct ihex_binrec *rec)
		{
		int next = ((be16_to_cpu(rec->len) + 5) & ~3) - 2;
		rec = (void *)&rec->data[next];
		const void *p = rec;

		return rec;
		return p + ALIGN(ihex_binrec_size(rec), 4);
		}

		static inline const struct ihex_binrec *

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