Simplify Multiply Operations in Array Indexing

The generated code might have multiply operations when indexing an element of an array. You can select the optimization parameter Simplify array indexing to replace multiply operations in the array index with a temporary variable. This optimization can improve execution speed by reducing the number of times the multiply operation executes.

Example Model

If you have the following model:

The Constant blocks have the following Constant value:

• Const1: reshape(1:30,[1 5 3 2])

• Const2: reshape(1:20,[1 5 2 2])

• Const3: reshape(1:90,[1 5 9 2])

The Concatenate block parameter Mode is set to Multidimensional array. The Constant blocks Sample time parameter is set to –1.

Generate Code

Building the model with the Simplify array indexing parameter turned off generates the following code:

int32_T i;
int32_T i_0;
int32_T i_1;

for (i = 0; i < 2; i++) {
  for (i_1 = 0; i_1 < 3; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[(i_0 + 5 * i_1) + 70 * i] =
        ex_arrayindex_P.Constant1_Value[(5 * i_1 + i_0) + 15 * i];
    }
  }
}

for (i = 0; i < 2; i++) {
  for (i_1 = 0; i_1 < 2; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[(i_0 + 5 * (i_1 + 3)) + 70 * i] =
        ex_arrayindex_P.Constant2_Value[(5 * i_1 + i_0) + 10 * i];
    }
  }
}

for (i = 0; i < 2; i++) {
  for (i_1 = 0; i_1 < 9; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[(i_0 + 5 * (i_1 + 5)) + 70 * i] =
        ex_arrayindex_P.Constant3_Value[(5 * i_1 + i_0) + 45 * i];
    }
  }
}

Generate Code with Optimization

Open the Configuration Parameters dialog box and select the Simplify array indexing parameter. Build the model again. In the generated code, [(i_0 + tmp_1) + tmp] replaces a multiply operation in the array index, [(i_0 + 5 * i_1) + 70 * i]. The generated code is now:

int32_T i;
int32_T i_0;
int32_T i_1;
int32_T tmp;
int32_T tmp_0;
int32_T tmp_1;

tmp = 0;
tmp_0 = 0;
for (i = 0; i < 2; i++) {
  tmp_1 = 0;
  for (i_1 = 0; i_1 < 3; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[(i_0 + tmp_1) + tmp] =
        ex_arrayindex_P.Constant1_Value[(i_0 + tmp_1) + tmp_0];
    }

    tmp_1 += 5;
  }

  tmp += 70;
  tmp_0 += 15;
}

tmp = 0;
tmp_0 = 0;
for (i = 0; i < 2; i++) {
  tmp_1 = 0;
  for (i_1 = 0; i_1 < 2; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[((i_0 + tmp_1) + tmp) + 15] =
        ex_arrayindex_P.Constant2_Value[(i_0 + tmp_1) + tmp_0];
    }

    tmp_1 += 5;
  }

  tmp += 70;
  tmp_0 += 10;
}

tmp = 0;
tmp_0 = 0;
for (i = 0; i < 2; i++) {
  tmp_1 = 0;
  for (i_1 = 0; i_1 < 9; i_1++) {
    for (i_0 = 0; i_0 < 5; i_0++) {
      ex_arrayindex_Y.Out[((i_0 + tmp_1) + tmp) + 25] =
        ex_arrayindex_P.Constant3_Value[(i_0 + tmp_1) + tmp_0];
    }

    tmp_1 += 5;
  }

  tmp += 70;
  tmp_0 += 45;
}