Messages in this thread Patch in this message | | | From | Andrey Smirnov <> | Subject | [PATCH 3/5] ihex: Simplify next record offset calculation | Date | Thu, 20 Dec 2018 23:28:39 -0800 |
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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> --- include/linux/ihex.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/include/linux/ihex.h b/include/linux/ihex.h index 9130f307a420..98cb5ce0b0a0 100644 --- a/include/linux/ihex.h +++ b/include/linux/ihex.h @@ -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 * -- 2.19.1
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