Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

VHDL integer to integer multiplication

Status
Not open for further replies.

shaiko

Advanced Member level 5
Joined
Aug 20, 2011
Messages
2,644
Helped
303
Reputation
608
Reaction score
297
Trophy points
1,363
Activity points
18,300
Hello,

This is the definition of the "numeric_std" multiplication function ( '*' )
Code:
  -- Id: A.15
  function "*" (L, R: UNSIGNED) return UNSIGNED;
  -- Result subtype: UNSIGNED((L'LENGTH+R'LENGTH-1) downto 0).
  -- Result: Performs the multiplication operation on two UNSIGNED vectors
  --         that may possibly be of different lengths.

  -- Id: A.16
  function "*" (L, R: SIGNED) return SIGNED;
  -- Result subtype: SIGNED((L'LENGTH+R'LENGTH-1) downto 0)
  -- Result: Multiplies two SIGNED vectors that may possibly be of
  --         different lengths.

  -- Id: A.17
  function "*" (L: UNSIGNED; R: NATURAL) return UNSIGNED;
  -- Result subtype: UNSIGNED((L'LENGTH+L'LENGTH-1) downto 0).
  -- Result: Multiplies an UNSIGNED vector, L, with a non-negative
  --         INTEGER, R. R is converted to an UNSIGNED vector of
  --         SIZE L'LENGTH before multiplication.

  -- Id: A.18
  function "*" (L: NATURAL; R: UNSIGNED) return UNSIGNED;
  -- Result subtype: UNSIGNED((R'LENGTH+R'LENGTH-1) downto 0).
  -- Result: Multiplies an UNSIGNED vector, R, with a non-negative
  --         INTEGER, L. L is converted to an UNSIGNED vector of
  --         SIZE R'LENGTH before multiplication.

  -- Id: A.19
  function "*" (L: SIGNED; R: INTEGER) return SIGNED;
  -- Result subtype: SIGNED((L'LENGTH+L'LENGTH-1) downto 0)
  -- Result: Multiplies a SIGNED vector, L, with an INTEGER, R. R is
  --         converted to a SIGNED vector of SIZE L'LENGTH before
  --         multiplication.

  -- Id: A.20
  function "*" (L: INTEGER; R: SIGNED) return SIGNED;
  -- Result subtype: SIGNED((R'LENGTH+R'LENGTH-1) downto 0)
  -- Result: Multiplies a SIGNED vector, R, with an INTEGER, L. L is
  --         converted to a SIGNED vector of SIZE R'LENGTH before
  --         multiplication.
It seems that multiplication of (L: INTEGER; R: INTEGER) isn't defined.
However,
The following code does compile in Modelsim:
Code:
signal x,y,z : integer ;
z <= x * y ;
2 Questions:

1. If it's undefined in the library - why does it work ?
2. Will the result be considered as signed or unsigned ?
 

std_match

Advanced Member level 4
Joined
Jul 9, 2010
Messages
1,215
Helped
451
Reputation
902
Reaction score
413
Trophy points
1,363
Location
Sweden
Activity points
9,420
integer is not a datatype from numeric_std. It is a built-in datatype.
No library/package is needed for integer*integer.
The result is an integer.
 
  • Like
Reactions: shaiko

    shaiko

    Points: 2
    Helpful Answer Positive Rating

shaiko

Advanced Member level 5
Joined
Aug 20, 2011
Messages
2,644
Helped
303
Reputation
608
Reaction score
297
Trophy points
1,363
Activity points
18,300
Thanks,
Is it possible to force an integer to be less then 32 bits long ?
 

std_match

Advanced Member level 4
Joined
Jul 9, 2010
Messages
1,215
Helped
451
Reputation
902
Reaction score
413
Trophy points
1,363
Location
Sweden
Activity points
9,420
Thanks,
Is it possible to force an integer to be less then 32 bits long ?

An integer has no bits, it is only a value. You can use "range" to restrict the possible values.
I think it is required that the internal representation in the simulator has at least 32 bits.

signed and unsigned have bits.
It is important to know that signed and unsigned from numeric_std wraps around when the max/min values are exceeded.
If an integer exceeds max/min there is an error in the simulation.
 
  • Like
Reactions: shaiko

    shaiko

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top