Moving the Current Read/Write Position Backward - 2025.1 English - UG1603

AI Engine-ML Kernel and Graph Programming Guide (UG1603)
Document ID
UG1603
Release Date
2025-05-29
Version
2025.1 English

In the following description, input_buffer<TYPE> and input_circular_buffer<TYPE> stands for any of the allowed input buffer port data types. Likewise, output_buffer<TYPE> and output_circular_buffer<TYPE> stands for any of the allowed output buffer port data types.

Table 1. Moving the Current Read/Write Position Backward
Purpose Input Buffer Port Type Output Buffer Port Type
To decrease the current read/write position. 
void simple(input_circular_buffer<TYPE> & in, output_buffer<TYPE> & out)
{
auto pIn  = aie::begin_random_circular(in);
...
TYPE data = *pIn--;
...
 
void simple(input_buffer<TYPE> & in, output_buffer<TYPE> & out)
{
auto pOut  = aie::begin_random_circular(out);
TYPE data;
...
*pOut-- = data;
...
To decrement the current read/write position by four times the underlying buffer port type. 
#define VECTOR_SIZE 4
void simple(input_circular_buffer<TYPE> & in, output_buffer<TYPE> & out)
{
auto pIn = aie:: begin_vector_random_circular <VECTOR_SIZE>(in);
...
v4TYPE data = *pIn--;
...
 
#define VECTOR_SIZE 4
void simple(input_buffer<TYPE> & in, output_circular_buffer<TYPE> & out)
{
auto pOut  = aie:: begin_vector_random_circular <VECTOR_SIZE>(out);
v4TYPE data;
...
*pOut-- = data;
...
To decrement the current read/write position by eight times the underlying buffer port type. 
#define VECTOR_SIZE 8
void simple(input_circular_buffer<TYPE> & in, output_buffer<TYPE> & out)
{
auto pIn = aie:: begin_vector_random_circular <VECTOR_SIZE>(in);
...
v8TYPE data = *pIn--;
...
 
#define VECTOR_SIZE 8
void simple(input_buffer<TYPE> & in, output_circular_buffer<TYPE> & out)
{
auto pOut  = aie:: begin_vector_random_circular <VECTOR_SIZE>(out);
v8TYPE data;
...
*pOut-- = data;
...