Invoking MADD instruction from C

Generally, C programmers don't have to worry about the assembly instructions that their C compiler generates. We have, however, received a few messages asking if the MPLAB C Compiler for PIC32 (aka MPLAB C32) supports the MADD instruction. Yes, it does. The compiler tries to avoid using the HI/LO registers, but the code below shows a sequence that invokes the MADD instruction (as of C32 1.02).

EDIT1: You'll need to build with at least the -O1 level of optimization.

int dp (int a[], int b[], int n);

int ary1[] = {1,2,3,4,5};
int ary2[] = {6,7,8,9,10};
volatile int testval;

int main(void)
{ 
 testval = dp (ary1, ary2, 5);
 while(1);
}

int dp (int a[], int b[], int n)
{
  /*
   *   move  a3,a0
   */

  int i;
  long long acc = (long long) a[0] * b[0];
  /*    
   *   lw v1,0(a1)
   *   lw a0,0(a0)
   */

  for (i = 1; i < n; i++)
  /*
   *   li t0,1
   *   slt   v0,t0,a2
   *   beqz  v0,9d00005c 
   *   mult  a0,v1
   *   addiu a1,a1,4
   *   addiu a0,a3,4
   *   addiu a2,a2,-1
   */

  acc += (long long) a[i] * b[i];
  /*
   *   lw t1,0(a0)
   *   lw a3,0(a1)
   *   addiu a2,a2,-1
   *   madd  t1,a3        <--- MADD instruction
   *   addiu a0,a0,4
   *   bnez  a2,9d000040 
   *   addiu a1,a1,4
   */

  return (acc >> 31);
  /*
   *   mflo  t3
   *   mfhi  t2
   *   srl   a1,t3,0x1f
   *   sll   a2,t2,0x1
   */
}
  /*
   *   jr ra
   *   or v0,a1,a2
   */