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old mail I sent with a REAL constant function example

min. size constant mults.

	kurt

ps. on vaction till sept. 20 (south pacific- yeah!!)



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>From kurt Thu Oct 23 22:34:27 1997
Date: Thu, 23 Oct 97 22:34:27 EDT
>From: kurt (Kurt Baty)
To: btf@boyd.com
Subject: BTF contant function example
Cc: kurt
Content-Type: X-sun-attachment
Content-Length: 3476


the function constant_bits in a constant function

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module constant_mult(a,product);
parameter	a_width = 8;
parameter	const_width = 8;
parameter	constant = 1;
input	[a_width-1:0]	a;
output	[a_width+const_width-1:0]	product;

wire	[a_width+const_width-1:0]	product;
wire	[const_width-1:0]	constant_wire;

assign	constant_wire = constant;
assign	product = a * constant_wire;

endmodule



---------------------------------------------------------------------------

module #(a_width,const_width,constant) constant_mult(a,product);
parameter	a_width = 8;
parameter	const_width = 8;
parameter	constant = 1;
input	[a_width-1:0]	a;
output	[a_width+const_width-1:0]	product;


function integer constant_bits;
input	integer	constant,return_sel;

integer		bit_value,pos_result,neg_result,count;
integer		i,j;
begin
  bit_value = constant_wire;
  pos_result = 0;
  neg_result = 0;
  count      = 0;
  for(i=0;i<=const_width;i=i+1) begin
    if( i <= const_width-3 ) begin
      if({bit_value[i+2],bit_value[i+1],bit_value[i]} == 3'b111) 
        for(j=i+3;j<=const_width;j=j+1) 
          if(!bit_value[j] && (&{bit_value[j-1],bit_value[j-2],bit_value[j-3]})) begin 
            pos_result[j] = 1'b1;
            bit_value[j:0] = pos_result[j:0];
            neg_result[i] = 1'b1;
          end
      else
        pos_result[i] := bit_value[i];
    end
    else
      pos_result[i] := bit_value[i];
    if(pos_result[i]) 
      count = count + 1;
    if(neg_result[i]) 
      count = count + 1;
  end
  if(|neg_result)
      count = count + 1;
  if(return_sel == 1)
  	constant_bits = pos_result;
  else if(return_sel == 2)
  	constant_bits = neg_result;
  else
  	constant_bits = count;
end
endfunction


parameter	pos_result = constant_bits(constant,1);
parameter	neg_result = constant_bits(constant,2);
parameter	count      = constant_bits(constant,3);
parameter	vsum_width = (a_width+const_width);
parameter	vector_in_width = vsum_width*count;

function [vector_in_width-1:0] make_vector_in;
input	[a_width-1:0]	a;

integer		ptr,i,j,k;
reg	[vector_in_width-1:0]  vector_in;
begin
  ptr = 0;
  for(i=0;i<=const_width;i=i+1) begin
    if(neg_result[i]) begin
      for(j=0;j<vsum_width;j=j+1) begin
        if(j < i) 
	  vector_in[ptr*vsum_width+j] = 1'b1;
        else if((j >= i) && (j-i < a_width)) 
	  vector_in[ptr*vsum_width+j] = !a[j-i];
        else if(j >= a_width) 
	  vector_in[ptr*vsum_width+j] = 1'b1;
      end
      ptr := ptr + 1;
    end
    if(pos_result[i]) begin
      for(j=0;j<vsum_width;j=j+1) begin
        if(j < i) 
	  vector_in[ptr*vsum_width+j] = 1'b0;
        else if((j >= i) && (j-i < a_width)) 
	  vector_in[ptr*vsum_width+j] = a[j-i];
        else if(j >= a_width) 
	  vector_in[ptr*vsum_width+j] = 1'b0;
      end
      ptr := ptr + 1;
    end
  end
  for(k=0;k<vsum_width;k=k+1) begin
    if(k <= const_width) 
      vector_in[ptr*vsum_width+k] = neg_result[k];
    else if(k > const_width) 
      vector_in[ptr*vsum_width+k] = 1'b0;
  end
  make_vector_in = vector_in;
end
endfunction

wire	[vsum_width-1:0]	product;
wire	[vector_in_width-1:0]	vector_in;

assign	vector_in = make_vector_in(a);

DW02_sum #(count,vsum_width) vsum(vector_in,product);

endmodule