set_directive_array_reshape - 2020.2 English

Vitis High-Level Synthesis User Guide (UG1399)
Document ID
UG1399
Release Date
2021-03-22
Version
2020.2 English

Description

Combines array partitioning with vertical array mapping to create a single new array with fewer elements but wider words.

The set_directive_array_reshape command has the following features:

  • Splits the array into multiple arrays (like set_directive_array_partition).
  • Automatically recombine the arrays vertically to create a new array with wider words.

Syntax

set_directive_array_reshape [OPTIONS] <location> <array>
  • <location> is the location (in the format function[/label]) that contains the array variable.
  • <array> is the array variable to be reshaped.

Options

-dim <integer>
Note: Relevant for multi-dimensional arrays only.
Specifies which dimension of the array is to be reshaped.
  • If the value is set to 0, all dimensions are partitioned with the specified options.
  • Any other value partitions only that dimension. For example, if the value is set 1, only the first dimension is partitioned.
-factor <integer>
Note: Relevant for type block or cyclic reshaping only.
Specifies the number of temporary smaller arrays to be created.
-object
Note: Relevant for container arrays only.
Applies reshape on the objects within the container. If the option is specified, all dimensions of the objects will be reshaped, but all dimensions of the container will be kept.
-type (block|cyclic|complete)
  • block reshaping creates smaller arrays from consecutive blocks of the original array. This effectively splits the array into N equal blocks where N is the integer defined by the -factor option and then combines the N blocks into a single array with word-width*N. The default is complete.
  • cyclic reshaping creates smaller arrays by interleaving elements from the original array. For example, if -factor 3 is used, element 0 is assigned to the first new array, element 1 to the second new array, element 2 is assigned to the third new array, and then element 3 is assigned to the first new array again. The final array is a vertical concatenation (word concatenation, to create longer words) of the new arrays into a single array.
  • complete reshaping decomposes the array into temporary individual elements and then recombines them into an array with a wider word. For a one-dimension array this is equivalent to creating a very-wide register (if the original array was N elements of M bits, the result is a register with N*M bits).

Examples

Reshapes 8-bit array AB[17] in function foo into a new 32-bit array with five elements.

Because four is not an integer factor of 13:

  • AB[17] is in the lower eight bits of the fifth element.
  • The remainder of the fifth element is unused.
set_directive_array_reshape -type block -factor 4 foo AB

Partitions array AB[6][4] in function foo, into a new array of dimension [6][2], in which dimension 2 is twice the width.

set_directive_array_reshape -type block -factor 2 -dim 2 foo AB

Reshapes 8-bit array AB[4][2][2] in function foo into a new single element array (a register), 4*2*2*8 (= 128)-bits wide.

set_directive_array_reshape -type complete -dim 0 foo AB

See Also