The testbench below is answer to my question. The result of conversion is stored in slv. The input file contains a column of real numbers of the type I mentioned in the question i.e single preciousion floating point numbers generated from a program probably written in C or C++. As expected, there is difference between real1 and real2 which is another thing I wanted to check.
The float_generic_pkg which is basis for the float_pkg defines the float32 as follows:
subtype float32 is float (8 downto -23);
Where the float type is:
subtype float is (resolved) UNRESOLVED_float;
Where the UNRESOLVED_float is actually:
type UNRESOLVED_float is array (INTEGER range <>) of STD_ULOGIC;
This means that the floating point type is fundamentally just a std_logic_vector and thus not the same thing as a real!
Anyway, the code sample below is answer to the question.
library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.MATH_REAL.ALL; use IEEE.float_pkg.all; library std; use std.textio.all; entity t_real_to_slv is end t_real_to_slv; architecture beh of t_real_to_slv is -- real number read from file signal real1: real; -- float resulting from conversion of real1 signal float1: float32; -- slv resulting from conversion of float1 signal slv: std_logic_vector(31 downto 0); -- float resulting from conversion of slv signal float2: float32; -- real number resulted from conversion of float type signal real2: real; -- difference between the real1 and real2 signal real_delta: real; begin process file text_in : text open read_mode is "../../../real_in.txt"; file text_out : text open write_mode is "../../dump_out.txt"; variable line_in, line_out : line; variable r_in, r_out : real; begin for i in 1 to 10 loop if(NOT ENDFILE(text_in)) then -- read the current line. readline(text_in,line_in); -- read the real number from input file line read(line_in, r_in); real1 <= r_in; wait for 1 ns; -- convert the real number to float32, the float32 -- is merely a float with limits 8, -23 float1 <= to_float(real1); wait for 1 ns; -- convert the float into std_logic_vector so we can -- have the binary representation of real1 slv <= std_logic_vector(float1); wait for 1 ns; -- now convert slv into float32 float2 <= to_float(slv); wait for 1 ns; -- now convert float32 into real type real2 <= to_real(float2); wait for 1 ns; -- calculate the difference between the real number found -- in the input text file and the real number real_delta <= real2 - real1; wait for 0 ns; -- write the original real number r_out := real1; write(line_out, r_out); write(line_out, ht); -- write the real number resulting from conversions r_out := real2; write(line_out, r_out); write(line_out, ht); -- write difference between the original real number -- and the one generated from conversions r_out := real_delta; write(line_out, r_out); writeline(text_out, line_out); -- verify that the floating point numbers are equal -- i.e no information is lost in conversion -- floa32->slv->float32; expected to pass assert float2 = float1 report "floating point values do not match" severity warning; -- verify that the floating point number read from the -- file is equal to the number resulting from conversions -- i.e no information is lost in conversion -- real->floa32->slv->float32->real; expected to fail assert real2 = real1 report "real values do not match" severity warning; end if; end loop; assert false report "end of test" severity failure; wait; end process; end architecture;
The gist of all this is these two lines:
real_to_slv := std_logic_vector(to_float(real_number)); slv_to_real_number := to_real(to_float(real_to_slv));
The slv must be declared as a 32 bit vector. Else, the conversions will fail at runtime. We need to use the float_pkg but not the float type itself in this case.
