hls::vector
objects in your code include the header file
hls_vector.h.Vector Data Type Usage
The vector data type is provided to easily model and synthesize SIMD-type
vector operations.
Vitis™ HLS vector data type
can be defined as follows, where T
is a primitive
or user-defined type with most of the arithmetic operations defined on it. N
is an integer greater than zero. Once a vector type
variable is declared it can be used like any other primitive type variable to
perform arithmetic and logic operations.
#include <hls_vector.h>
hls::vector<T,N> aVec;
T
and N
are integer powers of 2.Memory Layout
For any vector type defined as hls::vector<T,N>
, the storage is guaranteed to be contiguous of
size sizeof(T)*N
and aligned to the greatest power
of 2 such that the allocated size is at least sizeof(T)*N
. In particular, when N
is
a power of 2 and sizeof(T)
is a power of 2, vector<T, N>
is aligned to its total size. This
matches vector implementation on most architectures.
sizeof(T)*N
is an integer power of 2, the allocated
size will be exactly sizeof(T)*N
, otherwise the
allocated size will be larger to make alignment possible.The following example shows the definition of a vector class that aligns itself as described above.
constexpr size_t gp2(size_t N)
{
return (N > 0 && N % 2 == 0) ? 2 * gp2(N / 2) : 1;
}
template<typename T, size_t N> class alignas(gp2(sizeof(T) * N)) vector
{
std::array<T, N> data;
};
Following are different examples of alignment:
hls::vector<char,8> char8Vec; // aligns on 8 Bytes boundary
hls::vector<int,8> int8Vec; // aligns on 32 byte boundary
Requirements and Dependencies
Vitis HLS vector types requires support for C++ 14 or later. It has the following dependencies on the standard headers:
-
<array>
-
std::array<T, N>
-
-
<cassert>
-
assert
-
-
<initializer_list>
-
std::initializer_list<T>
-
Supported Operations
- Initialization:
hls::vector<int, 4> x; // uninitialized hls::vector<int, 4> y = 10; // scalar initialized: all elements set to 10 hls::vector<int, 4> z = {0, 1, 2, 3}; // initializer list (must have 4 elements) hls::vector<ap_int, 4> a; // uninitialized arbitrary precision data type
- Access:The operator[] enables access to individual elements of the vector, similar to a standard array:
x[i] = ...; // set the element at index i ... = x[i]; // value of the element at index i
- Arithmetic:
They are defined recursively, relying on the matching operation on
T
.Table 1. Arithmetic Operation Operation In Place Expression Reduction (Left Fold) Addition +=
+
reduce_add
Subtraction -=
-
non-associative Multiplication *=
*
reduce_mult
Division /=
/
non-associative Remainder %=
%
non-associative Bitwise AND &=
&
reduce_and
Bitwise OR |=
|
reduce_or
Bitwise XOR ^=
^
reduce_xor
Shift Left <<=
<<
non-associative Shift Right >>=
>>
non-associative Pre-increment ++x
none unary operator Pre-decrement --x
none unary operator Post-increment x++
none unary operator Post-decrement x--
none unary operator - Comparison:
Lexicographic order on vectors (returns bool):
Table 2. Operation Operation Expression Less than <
Less or equal <=
Equal ==
Different !=
Greater or equal >=
Greater than >