The compiler automatically generates DMAC instructions if the compiler recognizes the C-language statements as a DMAC opportunity and the compiler can verify that the data addresses being operated upon are 32-bit aligned. This is the best scenario, because it requires no code modification aside from data alignment pragmas. The following is an example:
int src1[N], src2[N];
#pragma DATA_ALIGN(src1,2); // int arrays must be 32-bit aligned
#pragma DATA_ALIGN(src2,2);
{...}
int i;
long res = 0;
for (i = 0; i < N; i++) // N must be a known even constant
res += (long)src1[i] * src2[i]; // Arrays must be accessed via array indices
At optimization levels >= -O2, the compiler generates a RPT || DMAC instruction for the example code above if N is a known even constant.
DMAC instructions can also shift the product left by 1 or right by 1 to 6 before accumulation. For example:
for (i = 0; i < N; i++)
res += (long)src1[i] * src2[i] >> 1; // product shifted right by 1