real number to 16 bit signed number

[hari]

hi
a) i want to convert a real number to 16 bit signed binary number.
the real number is 2E15-1.so how should i do it.do we have any
default packages for that.

thanks
hari

 

[Alan Fitch]

hi
a) i want to convert a real number to 16 bit signed binary number.
the real number is 2E15-1.so how should i do it.do we have any
default packages for that.

Assuming you mean SIGNED from Numeric_std, you could use

library IEEE;
use IEEE.NUMERIC_STD.all;

....

signal S : SIGNED(15 downto 0)
signal V : STD_LOGIC_VECTOR(15 downto 0);
signal I : INTEGER range -2**15 to 2**15-1;
signal R : real;

....

S <= to_signed(INTEGER(R),16));

If you want to go to std_logic_vector, then

V <= STD_LOGIC_VECTOR(to_signed(INTEGER(R),16)));

If you meant just an integer, then they are closely related so you can
just
do

I <= INTEGER(R);


The conversion rounds.

regards

Alan

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[paris]

hi
a) i want to convert a real number to 16 bit signed binary number.
the real number is 2E15-1.so how should i do it.do we have any
default packages for that.

thanks
hari

i guess you meant 2 "to the power of" 15 minus 1 = 32768-1 am i right? if
so, then it's an integer and therefore it's trivial to convert it, but then,
the whole thing seem too trivial

 

[hari]

sorry the real number is 0.9990234375 and i want to convert it to a 16
bit binary number .can u guys help me out.
thanks
hari

 

[hamilton]

Is standard C code OK ???

 

[hari]

i have to do it in vhdl.but yes the c code should be ok.i can try
converting it to vhdl.
thanks
hariprasath

 

[hamilton]

OK,

float sample;
int answer;

answer = int( sample );


simplified would be:

if( sample < 1.0000 )
answer = 0;



Did I miss something or did you not give enough information ??

 

[saket.sona]

sorry the real number is 0.9990234375 and i want to convert it to a 16
bit binary number .can u guys help me out.
thanks
hari

You need to use method as described S <= to_signed(INTEGER(R),16));
the only catch is that you first need to convert the real data R to integer by scaling meaningfully, which means just multiply the R * 32768 first so that +1.0 and -1.0 are replaced by two highest and lowest of 16 bits. and then use that R for above formula. so in the end you will have something like S <= to_signed(INTEGER(R*32768),16)); although this step R*32768 has to be done seperately first.
i hope it helps.