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    9fb4ab4d
    ihex: Simplify next record offset calculation · 9fb4ab4d
    Andrey Smirnov authored
    
    
    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: default avatarAndrey Smirnov <andrew.smirnov@gmail.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    9fb4ab4d
    ihex: Simplify next record offset calculation
    Andrey Smirnov authored
    
    
    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: default avatarAndrey Smirnov <andrew.smirnov@gmail.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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