FixedPoint Designer™ must determine the properties of all variables in the MATLAB^{®} files at compile time. To infer variable properties in MATLAB files, FixedPoint Designer must be able to identify the properties of the inputs to the primary function, also known as the toplevel or entrypoint function. Therefore, if your primary function has inputs, you must specify the properties of these inputs, to FixedPoint Designer. If your primary function has no input parameters, FixedPoint Designer can compile your MATLAB file without modification. You do not need to specify properties of inputs to local functions or external functions called by the primary function.
If your primary function has inputs, you must specify the following properties for each input.
For  Specify properties  

Class  Size  Complexity  numerictype  fimath  
Fixedpoint inputs 





Each field in a structure input  
Other inputs 



FixedPoint Designer assigns the following default values for properties of primary function inputs.
Property  Default 

class  double 
size  scalar 
complexity  real 
numerictype  No default 
fimath  MATLAB default fimath object 
The following table presents the class names supported by FixedPoint Designer.
Class Name  Description 

logical  Logical array of true and false values 
char  Character array 
int8  8bit signed integer array 
uint8  8bit unsigned integer array 
int16  16bit signed integer array 
uint16  16bit unsigned integer array 
int32  32bit signed integer array 
uint32  32bit unsigned integer array 
int64  64bit signed integer array 
uint64  64–bit unsigned integer array 
single  Singleprecision floatingpoint or fixedpoint number array 
double  Doubleprecision floatingpoint or fixedpoint number array 
struct  Structure array 
embedded.fi  Fixedpoint number array 
When specifying the properties of primary inputs, follow these rules.
You must specify the class of all primary inputs. If you do not specify the size or complexity of primary inputs, they default to real scalars.
For each primary function input whose class is fixed
point (fi
), you must specify the input numerictype
and fimath
properties.
For each primary function
input whose class is struct
, you must specify the
properties of each of its fields in the order that they appear in
the structure definition.
Method  Advantages  Disadvantages  


 
Define Input Properties by Example at the Command Line


 


The fiaccel
function provides a commandline
option args
for specifying the properties of primary
(entrypoint) function inputs as a cell array of example values. The
cell array can be a variable or literal array of constant values.
Using this option, you specify the properties of inputs at the same
time as you generate code for the MATLAB function with fiaccel
.
When using the args
commandline option
to define properties by example, follow these rules:
The cell array of sample values must contain the same number of elements as primary function inputs.
The order of elements in the cell array must correspond to the order in which inputs appear in the primary function signature — for example, the first element in the cell array defines the properties of the first primary function input.
Note:
If you specify an empty cell array with the 
Consider a function that adds its two inputs:
function y = emcf(u,v) %#codegen % The directive %#codegen indicates that you % intend to generate code for this algorithm y = u + v;
The following examples show how to specify different properties
of the primary inputs u
and v
by
example at the command line:
Use a literal cell array of constants to specify that both inputs are real, scalar, fixedpoint values:
fiaccel o emcfx emcf ... args {fi(0,1,16,15),fi(0,1,16,15)}
Use a literal cell array of constants to specify that
input u
is an unsigned 16bit, 1by4 vector and
input v
is a scalar, fixedpoint value:
fiaccel o emcfx emcf ... args {zeros(1,4,'uint16'),fi(0,1,16,15)}
Assign sample values to a cell array variable to specify that both inputs are real, unsigned 8bit integer vectors:
a = fi([1;2;3;4],0,8,0) b = fi([5;6;7;8],0,8,0) ex = {a,b} fiaccel o emcfx emcf args ex
Consider a function that calculates the square root of a fixedpoint number:
function y = sqrtfi(x) %#codegen y = sqrt(x);
To specify the properties of the primary fixedpoint input x
by
example on the MATLAB command line, follow these steps:
Define the numerictype
properties
for x
, as in this example:
T = numerictype('WordLength',32,... 'FractionLength',23,'Signed',true);
Define the fimath
properties for x
,
as in this example:
F = fimath('SumMode','SpecifyPrecision',... 'SumWordLength',32,'SumFractionLength',23,... 'ProductMode','SpecifyPrecision', ... ProductWordLength',32,'ProductFractionLength',23);
Create a fixedpoint variable with the numerictype
and fimath
properties
you defined, as in this example:
myeg = { fi(4.0,T,F) };
Compile the function sqrtfi
using
the fiaccel
command, passing the variable myeg
as
the argument to theargs
option, as in this example:
fiaccel sqrtfi args myeg;
If you know that your primary inputs do not change at run time, you can reduce overhead in the generated code by specifying that the primary inputs are constant values. Constant inputs are commonly used for flags that control how an algorithm executes and values that specify the sizes or types of data.
To specify that inputs are constants, use the args
commandline
option with a coder.Constant
object.
To specify that an input is a constant with the size, class, complexity,
and value of constant_input
, use the following
syntax:
args {coder.Constant(constant_input
)}
fiaccel
compiles constant function inputs
into the generated code. As a result, the MEX function signature differs
from the MATLAB function signature. At run time, you supply the
constant argument to the MATLAB function, but not to the MEX
function.
For example, consider the following function identity
which
copies its input to its output:
function y = identity(u) %#codegen y = u;
To generate a MEX function identity_mex
with
a constant input, type the following command at the MATLAB prompt:
fiaccel o identity_mex identity... args {coder.Constant(fi(0.1,1,16,15))}
To run the MATLAB function, supply the constant argument as follows:
identity(fi(0.1,1,16,15))
You get the following result:
ans = 0.1000
Now, try running the MEX function with this command:
identity_mex
You should get the same answer.
Suppose that you define a structure tmp
in
the MATLAB workspace to specify the dimensions of a matrix, as
follows:
tmp = struct('rows', 2, 'cols', 3);
The following MATLAB function rowcol
accepts
a structure input p
to define matrix y
:
function y = rowcol(u,p) %#codegen y = fi(zeros(p.rows,p.cols),1,16,15) + u;
The following example shows how to specify that primary input u
is
a double scalar variable and primary input p
is
a constant structure:
fiaccel rowcol ... args {fi(0,1,16,15),coder.Constant(tmp)}
To run this code, use
u = fi(0.5,1,16,15) y_m = rowcol(u,tmp) y_mex = rowcol_mex(u)
Variablesize data is data whose size might change at run time. MATLAB supports
bounded and unbounded variablesize data for code generation. Bounded
variablesize data has fixed upper bounds. This data can
be allocated statically on the stack or dynamically on the heap. Unbounded
variablesize data does not have fixed upper bounds. This
data must be allocated on the heap. You can define inputs to have
one or more variablesize dimensions — and specify their upper
bounds — using the args
option and coder.typeof
function:
args {coder.typeof(example_value, size_vector, variable_dims}
Same class and complexity as example_value
Same size and upper bounds as size_vector
Variable dimensions specified by variable_dims
When you enable dynamic memory allocation, you can specify Inf
in
the size vector for dimensions with unknown upper bounds at compile
time.
When variable_dims
is a scalar, it
is applied to all the dimensions,
with the following exceptions:
If the dimension is 1 or 0, which are fixed.
If the dimension is unbounded, which is always variable size.
Write a function that computes the sum of every n
elements
of a vector A
and stores them in a vector B
:
function B = nway(A,n) %#codegen % Compute sum of every N elements of A and put them in B. coder.extrinsic('error'); Tb = numerictype(1,32,24); if ((mod(numel(A),n) == 0) && ... (n>=1 && n<=numel(A))) B = fi(zeros(1,numel(A)/n),Tb); k = 1; for i = 1 : numel(A)/n B(i) = sum(A(k + (0:n1))); k = k + n; end else B = fi(zeros(1,0),Tb); error('n<=0 or does not divide evenly'); end
Specify the first input A
as a fi
object.
Its first dimension stays fixed in size and its second dimension can
grow to an upper bound of 100. Specify the second input n
as
a double scalar.
fiaccel nway ... args {coder.typeof(fi(0,1,16,15,'SumMode','KeepLSB'),[1 100],1),0}... report
As an alternative, assign the coder.typeof
expression
to a MATLAB variable, then pass the variable as an argument to args
:
vareg = coder.typeof(fi(0,1,16,15,'SumMode','KeepLSB'),[1 100],1) fiaccel nway args {vareg, double(0)} report