memcpy Optimization - MATLAB & Simulink (original) (raw)
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To optimize generated code that copies consecutive array elements, the code generator tries to replace the code with a memcpy call. Amemcpy call can be more efficient than afor-loop or multiple, consecutive element assignments. This table shows examples of generated C code with and without the memcpy optimization.
| Code Generated with memcpy Optimization | Code Generated Without memcpy Optimization |
|---|---|
| memcpy(&C[0], &A[0], 10000U * sizeof(double)); | for (i0 = 0; i0 < 10000; i0++) { C[i0] = A[i0]; |
| memcpy(&Z[0], &X[0],1000U * sizeof(double)); | Z[0] = X[0]; Z[1] = X[1]; Z[2] = X[2]; ... Z[999] = X[999]; |
To enable or disable the memcpy optimization:
- At the command line, set the code configuration object property
EnableMemcpytotrueorfalse. The default value istrue. - In the MATLAB® Coder™ app, set Use memcpy for vector assignment to
YesorNo. The default value isYes.
When the memcpy optimization is enabled, the use ofmemcpy depends on the number of bytes to copy. The number of bytes to copy 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 copy is known at compile time, then the code generator produces a
memcpycall only when the number of bytes is greater than or equal to thememcpythreshold. - If the number of elements is not known at compile time, then the code generator produces a
memcpycall without regard to the threshold.
The default memcpy 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).
The memset optimization also uses thememcpy threshold.
In certain cases, the code generator can produce a memcpy call without regard to the EnableMemcpy orMemcpyThreshold parameters, or their equivalent settings in the app.