To optimize generated code that assigns a literal constant to
consecutive array elements, the code generator tries to replace the
code with a memset call. A memset call
can be more efficient than code, such as a for-loop
or multiple, consecutive element assignments.
| Code Generated with the memset Optimization | Code Generated without the memset Optimization |
|---|---|
memset(&Y[0], 125, 100U * sizeof(signed char)); | for (i = 0; i < 100; i++) {
Y[i] = 125; |
memset(&Y[0], 0, 10000U * sizeof(double)); | for (i0 = 0; i0 < 10000; i0++) {
Y[i0] = 0.0; |
memset(&Z[0], 0, 1000U * sizeof(double)); | Z[0] = 0.0; Z[1] = 0.0; Z[2] = 0.0; ... Z[999] = 0.0; |
To assign an integer constant to consecutive array elements,
the code generator invokes the memset optimization
when the following conditions are true:
The constant is a literal constant. For example, X[i]
= 5.
For a nonzero constant:
The type of the constant is not multiword.
The length in bits of the type of the constant is
the same as the length in bits of the C char type
that the hardware supports.
The number of bytes to assign is greater than or equal
to the memset optimization threshold. The number
of bytes to assign is the number of array elements multiplied by the
number of bytes required for the C/C++ data type.
The memset optimization threshold
is the same as the memcpy optimization threshold.
The default threshold is 64 bytes. To change the threshold:
At the command line, set the code configuration object
property MemcpyThreshold.
In the MATLAB® Coder™ app, set Memcpy threshold (bytes).
To assign a float or double 0 to consecutive array elements,
the code generator invokes the memset optimization
when the following conditions are true:
The constant is a literal constant. For example, X[i]
= 0.0.
The memset optimization is enabled
for assignment of float or double 0 to consecutive array elements.
The number of bytes to assign is greater than or equal
to the memset optimization threshold. The number
of bytes to assign is the number of array elements multiplied by the
number of bytes required for the C/C++ data type.
To enable or disable the memset optimization
for assignment of float or double 0 to consecutive array elements:
At the command line, set the code configuration object
property InitFltsAndDblsToZero to true or false,
respectively. The default value is true.
In the MATLAB Coder app, set Use memset
to initialize floats and doubles to 0.0 to Yes or No respectively.
The default value is Yes.
The memset optimization threshold
is the same as the memcpy optimization threshold.
The default threshold is 64 bytes. To change the threshold:
At the command line, set the code configuration object
property MemcpyThreshold.
In the MATLAB Coder app, set Memcpy threshold (bytes).