CODEWITHSUNDEEP
x86ssesimd
quartz
quartz

Reputation: 757

How to count the number of bytes which lies in some range using SSE?

I want to write a c program which counts the number of bytes in a range a...c with below code: 

char a[16], b[16], c[16];  
int counter = 0; 
for(i = 0;  i < 16; i++)  
{  
  if((a[i] < b[i]) && (b[i] < c[i]))  
  counter++;  
}  
return counter;

I am planning to do something like this 

__m128i result1 = _mm_cmpgt_epi8 (b, a);  
__m128i result2 = _mm_cmplt_epi8 (b, c);  
unsigned short out1 = _mm_movemask_epi8(result1);  
unsigned short out2 = _mm_movemask_epi8(result2);  
unsigned short out3 = out1 & out2;  
unsigned short out4 = _mm_popcnt_u32(out3);

Is my method correct? Is there is a better way to do this?

Upvotes: 2

Views: 396

Answers (1)

Jason R
Jason R

Reputation: 11768

Your approach looks pretty reasonable. I think you could save an instruction by doing the AND inside the SIMD registers, like this:

__m128i result1 = _mm_cmpgt_epi8 (b, a);
__m128i result2 = _mm_cmplt_epi8 (b, c);
__m128i mask = _mm_and_si128(result1, result2);
int mask2 = _mm_movemask_epi8(mask);
int counter = _mm_popcnt_u32(mask2);

Upvotes: 5

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