121 lines
4.0 KiB
VHDL
121 lines
4.0 KiB
VHDL
library ieee;
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use ieee.std_logic_1164.all;
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use ieee.numeric_std.all;
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package my_math_pkg is
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function sum_limit(i1, i2 : signed) return signed;
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function sub_limit(i1, i2 : signed) return signed;
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function sum_limit(i1, i2 : unsigned) return unsigned;
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function extend(x : signed; len : natural) return signed;
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function extend(x : unsigned; len : natural) return unsigned;
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function left_align(x : signed; len : natural) return signed;
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function left_scale(x : signed; sh : natural) return signed;
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-- function shift_right(x : signed; positions: natural) return signed;
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end;
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package body my_math_pkg is
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function sum_limit(i1, i2 : signed) return signed is
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variable o : signed(i1'range);
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begin
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assert i1'length = i2'length
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report "i1 and i2 should have the same length!"
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severity failure;
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o := i1 + i2;
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if (i1(i1'left) = i2(i2'left)) and (o(o'left) /= i1(i1'left)) then
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if i1(i1'left)='1' then
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o := to_signed(-(2**(o'length-1)), o'length);
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else
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o := to_signed(2**(o'length-1) - 1, o'length);
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end if;
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end if;
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return o;
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end function;
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function sub_limit(i1, i2 : signed) return signed is
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variable o : signed(i1'range);
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begin
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assert i1'length = i2'length
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report "i1 and i2 should have the same length!"
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severity failure;
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o := i1 - i2;
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if (i1(i1'left) /= i2(i2'left)) and (o(o'left) /= i1(i1'left)) then
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if i1(i1'left)='1' then
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o := to_signed(-(2**(o'length-1)), o'length);
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else
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o := to_signed(2**(o'length-1) - 1, o'length);
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end if;
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end if;
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return o;
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end function;
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function sum_limit(i1, i2 : unsigned) return unsigned is
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variable o : unsigned(i1'length downto 0);
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begin
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o := ('0' & i1) + i2;
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if o(o'left)='1' then
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o := (others => '1');
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end if;
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return o(i1'length-1 downto 0);
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end function;
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function extend(x : signed; len : natural) return signed is
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variable ret : signed(len-1 downto 0);
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alias a : signed(x'length-1 downto 0) is x;
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begin
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ret := (others => x(x'left));
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ret(a'range) := a;
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return ret;
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end function extend;
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function extend(x : unsigned; len : natural) return unsigned is
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variable ret : unsigned(len-1 downto 0);
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alias a : unsigned(x'length-1 downto 0) is x;
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begin
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ret := (others => '0');
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ret(a'range) := a;
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return ret;
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end function extend;
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function left_align(x : signed; len : natural) return signed is
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variable ret : signed(len-1 downto 0);
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begin
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ret := (others => '0');
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ret(len-1 downto len-x'length) := x;
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return ret;
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end function left_align;
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function left_scale(x : signed; sh : natural) return signed is
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alias a : signed(x'length-1 downto 0) is x;
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variable ret : signed(x'length-(1+sh) downto 0);
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variable top : signed(sh downto 0);
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begin
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if sh=0 then
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return x;
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end if;
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top := a(a'high downto a'high-sh);
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if (top = -1) or (top = 0) then -- can shift without getting punished!
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ret := a(ret'range);
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elsif a(a'high)='1' then -- negative and can't shift, so max neg:
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ret := (others => '0');
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ret(ret'high) := '1';
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else -- positive and can't shift, so max pos
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ret := (others => '1');
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ret(ret'high) := '0';
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end if;
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return ret;
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end function left_scale;
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-- function shift_right(x : signed; positions: natural) return signed is
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-- alias a : signed(x'length-1 downto 0) is x;
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-- variable ret : signed(x'length-1 downto 0);
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-- begin
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-- ret := (others => x(x'left));
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-- ret(a'left-positions downto 0) := a(a'left downto positions);
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-- return ret;
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-- end function shift_right;
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end;
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