Struct-Fields Partitioning

Struct-fields partitioning partitions a (array of) struct argument / variable into its individual fields such that each field is a partition. Unlike complete partitioning, if a field in the partitioned struct is an aggregate type (struct or array), the field is not further partitioned to its elements. Note that applying Struct-fields partitioning to an array-of-struct creates an array for each field in the struct. Unaccessed partitions (fields) are discarded, but the unaccessed elements in an aggreagte partition (field) are not discarded.

Example

struct Ty {
    struct SubTy {
        int a;
        int b;
    };
    char x;
    short y[2];
    SubTy z;
};

int sum(Ty array[8]) {
#pragma HLS function top
#pragma HLS memory partition argument(array) type(struct_fields)
    int result = 0;
    for (int i = 0; i < 8; i++) {
        result += array[i].x + array[i].y[0] + array[i].z.a;
    }
    return result;
}

The example above shows array, an array of struct of type Ty, is partitioned using Struct-fields partitioning. With the user-specified partitioning, SmartHLS™ outputs messages to the console stating that the argument set to be partitioned and how many partitions are created. The three partitions are array.x[8], array.y[8][2], and array.z[8], where the 8-element dimensions are inherited from the original array size.

Info: Found user specified memory: "array" on line 15 of struct_sum.cpp, with partition type: Fields, partition dimension: 0.
Info: Partitioning memory: array into 3 partitions.

The summary report from SmartHLS lists the 3 partitions created from the fields of the struct. Note that the array field Ty.y has one partition, and similarly the struct field Ty.z

+---------------------------------------------------------------------------+
| I/O Memories                                                              |
+---------+-----------------------+------+-------------+------------+-------+
| Name    | Accessing Function(s) | Type | Size [Bits] | Data Width | Depth |
+---------+-----------------------+------+-------------+------------+-------+
| array_x | sum                   | ROM  | 0           | 8          | 0     |
| array_y | sum                   | ROM  | 0           | 16         | 0     |
| array_z | sum                   | ROM  | 0           | 64         | 0     |
+---------+-----------------------+------+-------------+------------+-------+