memset Optimization - MATLAB & Simulink (original) (raw)

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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. Amemset call can be more efficient than afor-loop or multiple, consecutive element assignments. This table shows examples of generated C code with and without memset.

The code generator can use the memset optimization for assignment of an integer constant or a floating-point zero. The use of memset depends on:

• The size of the value to assign. The size must meet the requirements for a C/C++ memset call.
• The number of bytes to assign. 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.
  • If the number of elements to assign is known at compile time, then the code generator produces a memset call only when the number of bytes is greater than or equal to the threshold.
  • If the number of elements is not known at compile time, then the code generator produces a memset call without regard to the threshold.

The memset optimization threshold is the same as thememcpy optimization threshold. The default threshold is 64 bytes. To change the threshold:

• At the command line, set the code configuration object propertyMemcpyThreshold.
• In the MATLAB® Coder™ app, set Memcpy threshold (bytes).

For assignment of floating-point zero, to enable or disable thememset optimization:

• At the command line, set the code configuration object propertyInitFltsAndDblsToZero to true orfalse. The default value istrue.
• In the MATLAB Coder app, set Use memset to initialize floats and doubles to 0.0 to Yes orNo. The default value isYes.

Related Topics

• memcpy Optimization
• MATLAB Coder Optimizations in Generated Code
• Optimize Generated C/C++ and MEX Code