CODEWITHSUNDEEP
ssesimd
SvinSimpe
SvinSimpe

Reputation: 870

What is the difference between non-packed and packed instruction in the context of SIMD-operations?

What is the difference between non-packed and packed instruction in the context of SIMD-operations?

I was reading an article on optimizing your code for SSE:

http://www.cortstratton.org/articles/OptimizingForSSE.php#batch

and this question arose when I read

"As an added bonus, movss is a non-packed instruction, which allows us to make better use of the parallel instruction decoders.."

So what is the difference?

Upvotes: 5

Views: 1623

Answers (2)

alexo_o
alexo_o

Reputation: 706

SSE supports two modes of operation:

  • Packed mode - instructions operate in parallel on all data operands
  • Scalar mode - instructions operate on the least significant pairs of packed data operands.

Source

Upvotes: 4

Codor
Codor

Reputation: 17605

To my understanding, packed means that conceptually more than one value is transferred or used as an operand, whereas non-packed means that only one value is is processed; non-packed means that no parallel processing takes place.

Upvotes: 4

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