Loop Interchange in C

• In C, the situation is exactly the opposite to Fortran:

• • The performance benefits in C are the same as in Fortran
  • In most practical situations, loop interchange (supported by the compiler) is much easier to achieve than index reversal.

Original loop:

#pragma no interchange

for(j=0; j<m; j++)

for(i=0; i<n; i++)

c[i][j]=a[i][j]+b[j][i];

Addressing of

c[i][j] and

a[i][j] are poor

Addressing of

b[j][i] is

optimal

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