Hi, Is there a way to add two unsigned numbers and extract only the x most significant bits from it in one step? I want something like this: sum <= resize(number1 + number2,4) Instead of: temp <= number1 + number2 sum <= temp(7 downto 4) The existing resize function in numeric_std drops the msb's, I want the lsb's dropped. Thanks in advance!

If your tool understands and supports the following: sum = (num1 + num2)/2**4; Then it is equivalent to discarding 4 bits from result unless it goes silly and creates a division module. alternatively if you can accept truncation errors then: sum <= num1(6 downto 4) + num2(6 downto 4); is almost equivalent but division is done on operands.

Thanks kaz for your reply! --- Quote Start --- sum = (num1 + num2)/2**4; --- Quote End --- I guess that in this case sum must have the same size as num1 and num2? I would rather have that sum already has the smaller size. --- Quote Start --- alternatively if you can accept truncation errors then: sum <= num1(6 downto 4) + num2(6 downto 4); --- Quote End --- I think I will go with this one. If there would be a way to avoid truncation errors, please let me know.

--- Quote Start --- If there would be a way to avoid truncation errors, please let me know. --- Quote End --- Yes. The code you origionall posted: temp <= number1 + number2 sum <= temp(7 downto 4)

Yes I know, but that is in two steps (clocks). I would rather have it in one.

If you want it in one clock, then make temp a variable rather than a signal.

Forum Discussion

Altera_Forum

Honored Contributor

14 years ago

Adding and resizing in one step

Hi,

Is there a way to add two unsigned numbers and extract only the x most significant bits from it in one step?

I want something like this:

sum <= resize(number1 + number2,4)

Instead of:

temp <= number1 + number2

sum <= temp(7 downto 4)

The existing resize function in numeric_std drops the msb's, I want the lsb's dropped.

Thanks in advance!

11 Replies

Altera_Forum
Honored Contributor
14 years ago
Sorry for my late reply on this. Thank you all for discussing this item!

I will go further with josyb's constuct, I didn't know you could use it like this.

--- Quote Start ---
sum <= unsigned(n1 + n2)(7 downto 4) ;

--- Quote End ---

Forum Discussion

Adding and resizing in one step

11 Replies

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