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### 13.12 Vector Operations

All normal RTL expressions can be used with vector modes; they are interpreted as operating on each part of the vector independently. Additionally, there are a few new expressions to describe specific vector operations.

`(vec_merge:m vec1 vec2 items)`

  This describes a merge operation between two vectors. The result is a vector of mode m; its elements are selected from either vec1 or vec2. Which elements are selected is described by items, which is a bit mask represented by a `const_int`; a zero bit indicates the corresponding element in the result vector is taken from vec2 while a set bit indicates it is taken from vec1.

`(vec_select:m vec1 selection)`

  This describes an operation that selects parts of a vector. vec1 is the source vector, and selection is a `parallel` that contains a `const_int` for each of the subparts of the result vector, giving the number of the source subpart that should be stored into it. The result mode m is either the submode for a single element of vec1 (if only one subpart is selected), or another vector mode with that element submode (if multiple subparts are selected).

`(vec_concat:m x1 x2)`

  Describes a vector concat operation. The result is a concatenation of the vectors or scalars x1 and x2; its length is the sum of the lengths of the two inputs.

`(vec_duplicate:m x)`

  This operation converts a scalar into a vector or a small vector into a larger one by duplicating the input values. The output vector mode must have the same submodes as the input vector mode or the scalar modes, and the number of output parts must be an integer multiple of the number of input parts.

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