asked on

bit change

i have binary number like this
1 0 1 1 1 0 1 0
i need to chage the bit value like bit 8 to bit 1
bit 7 to bit2
bit 6 to bit 3
bit 5 to bit 4
when changed the binary number will become 0 1 0 1 1 1 0 1
how to implemnt this using the bit operators

debuggerau

depends on your libraries, but these should help.
You could use assembler, as this has rotate functions...

david.tribble.com/text/c0xrot.htm
www.devx.com/tips/Tip/14043
http://www.programmersheaven.com/mb/CandCPP/79561/79691/ReadMessage.aspx?S=B20000

Then I found this...
http://forums.devarticles.com/c-c-help-52/c-code-to-rotate-a-bit-in-a-given-number-50277.html

Hope that helps.

ozo

The fastest way is probably with a 256 byte lookup table with all the reversed numbers pre computed

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ozo

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prasad2315

ASKER

i need to he exchange the bit position like shown below
the bibnary number is
b7 b6 b5 b4 b3 b2 b1 b0
after the exchangeof the bits the binary number will be
b0 b1 b2 b3 b4 b5 b6 b7
what will be the fastest implementation

Infinity08

>> what will be the fastest implementation

ozo already answered that. Which part do you want clarified ?

prasad2315

ASKER

i want a generic implementation that wil work for all the numbers

Infinity08

>> i want a generic implementation that wil work for all the numbers

Both solutions shown by ozo are generic. The lookup table, as ozo said, is the fastest.

ozo

A table lookup will work for all the numbers if the table is correctly set up for all the numbers.

Infinity08

Thatis, if you mean by "all the numbers" all 8bit types. For larger types, the lookup table becomes impractical, and you should favor ozo's second solution (with a few minor changes to account for the increased size).