CODEWITHSUNDEEP
armsimdneoncortex-a
studinstru
studinstru

Reputation: 124

if condition in loop and neon SIMD

I am trying to write the neon level SIMD for below scalar code :

Scalar code :

  int *xt = new int[50];
  float32_t input1[16] = {12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,12.0f,};
  float32_t input2[16] = {13.0f,12.0f,9.0f,12.0f,12.0f,12.0f,12.0f,12.0f,13.0f,12.0f,9.0f,12.0f,12.0f,12.0f,12.0f,12.0f};
  float32_t threshq    = 13.0f;
  uint32_t corners_count = 0;
  float32_t threshq =13.0f;
  for (uint32_t x = 0; x < 16; x++)
  {
      if ( (input1[x] == input2[x]) && (input2[x] > threshq) )
         {
             xt[corners_count] = x ;
         }
 }

Neon:

   float32x4_t t1,t2,t3;
   uint32x4_t rq1,rq2,rq3;
   t1 = vld1q_f32(input1);       // 12 12 12 12
   t2 = vld1q_f32(input2);       // 13 12 09 12
   t3 = vdupq_n_f32(threshq);    // 13 13 13 13
   rq1 = vceqq_f32(t1,t2);       // condition to check for input1 equal to input2
   rq2 = vcgtq_f32(t1,t3);       // condition to check for input1 greater than to threshold
   rq3 = vandq_u32(rq1,rq2);     // anding the result of two conditions
   for( int i = 0;i < 4; i++){
    corners_count = corners_count + rq3[i];
   //...Not able to write a logic in neon for the same
   }

I am not able to write a logic in Neon . Can anyone really guide me for the same .I am totally got tired in thinking about this logic

Upvotes: 0

Views: 1025

Answers (1)

Paul R
Paul R

Reputation: 213120

Because of the dependencies in your loop I think you need to re-factor your code into a SIMD loop followed by a scalar loop. Pseudo code:

// SIMD loop
for each set of 4 float elements
    apply SIMD threshold test
    store 4 x bool results in temp[]

// scalar loop
for each bool element in temp[]
    if temp[x]
        xt[corners_count] = x
        corner_count++

This way you get the benefits of SIMD for most of the operations, and you just have to resort to scalar code for the last part.

Upvotes: 1

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