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swap_lw_bytes(9r)
Contents
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swap_lw_bytes, swap_word_bytes, swap_words - General: Perform
byte-swapping operations
unsigned int swap_lw_bytes(
unsigned int buffer ); unsigned int
swap_word_bytes(
unsigned int buffer ); unsigned int swap_words(
unsigned int buffer );
Specifies a 32-bit (4 bytes) quantity.
The swap_lw_bytes interface performs a longword byte swap.
The swap_word_bytes interface performs a short word byte
swap. The swap_words interface performs a word byte swap.
Many computer vendors support devices that use a big
endian model of byte ordering. Because Digital devices
support the little endian model of byte ordering, there is
a need for these byte-swapping interfaces. In addition,
some buses (for example, the VMEbus) can have specific or
implied byte ordering that may require the use of these
interfaces.
Given that a longword is equal to 4 bytes; a short word is
equal to 2 bytes; and 1 byte is equal to 8 bits, these
interfaces swap bytes as follows: The swap_lw_bytes interface
takes the 32-bit quantity specified by the buffer
argument and swaps all 4 bytes. The swap_word_bytes
interface takes the 32-bit quantity specified by the
buffer argument and swaps the individual bytes that make
up each word of the 32-bit quantity. The swap_words
interface takes the 32-bit quantity specified by the
buffer argument and swaps the two 16-bit words.
The following illustration compares the byte swapping performed
by these interfaces.
31 0
+---+---+---+---+ Starting value: |
a | b | c | d |
+---+---+---+---+
Long word byte swap
(swap_lw_bytes)
31 0
+---+---+---+---+ Ending value: |
d | c | b | a |
+-------+---+---+
Short word byte swap
(swap_word_bytes)
31 0
+---+---+---+---+ Ending value: |
b | a | d | c |
+---+---+---+---+
31 0
+---+---+---+---+ Starting value: |
ab | cd |
+---+---+---+---+
Word byte swap
(swap_words)
31 0
+---+---+---+---+ Ending value: |
cd | ab |
+---+---+---+---+
Upon successful completion, these interfaces return the
swapped bytes.
swap_lw_bytes(9r)
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