DVD Studio Pro - Using Bit-Wise Operations

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Using Bit-Wise Operations

More often than not, when working with the SPRM values, you will only be interested in
certain bits of each 16-bit value. The “bit-wise” operations (and, or, and exclusive or),
make it possible to mask the bits that are not needed, allowing you to determine the
states of the specific bits you need.

Note: You need to have a basic understanding of working with binary numbers to be
able to use these operations.

511

Chapter 20

Creating Scripts

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Suppose you need to find out whether the DVD player is configured for a 4:3 or 16:9
aspect ratio monitor. To determine this, you only need to look at bits 10 and 11 of SPRM
14. You can use the “bit-wise and” operation to mask all bits except 10 and 11, making
it possible to easily determine the aspect ratio status without having to be concerned
with the other bits.

x

0
0

x

0
0

x

0
0

x

0
0

0/1

1

0/1

0/1

1

0/1

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

x

0
0

15

Bits

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

SPRM 14
And value
Result

Referring to the above table, the x’s in the SPRM 14 value represent bits that are not
needed. Bits 10 and 11 use “0/1” to indicate bits that you want to retain—these may be
set to either 0 or 1. When performing an AND operation, placing 0 in the bits you want
to mask results in their being cancelled out, regardless of their state. Placing 1 in the bits
you want to retain passes them to the result as is—a 0 is still a 0 and a 1 is still a 1. In this
case, an AND value of 3072 produces the proper masking.

The value of the result produces four possible answers: 0, 1024, 2048, and 3072. In the
case of SPRM 14, 0 indicates the DVD player is set to 4:3, and 3072 indicates it is set to
16:9 (the values of 1024 and 2048 are either not specified or reserved).