Emptiness Test - 2021.2 English

Vitis High-Level Synthesis User Guide (UG1399)

Document ID
Release Date
2021.2 English
bool empty(void)

Returns true if the hls::stream<> is empty.

// Usage of bool empty(void)

hls::stream<int> my_stream;
int dst_var;
bool stream_empty;

stream_empty = my_stream.empty();

The following example shows how a combination of non-blocking accesses and full/empty tests can provide error handling functionality when the RTL FIFOs are full or empty:

#include "hls_stream.h"
using namespace hls;

typedef struct {
   short    data;
   bool     valid;
   bool     invert;
} input_interface;

bool invert(stream<input_interface>& in_data_1,
            stream<input_interface>& in_data_2,
            stream<short>& output
  ) {
  input_interface in;
  bool full_n;

// Read an input value or return
  if (!in_data_1.read_nb(in))
      if (!in_data_2.read_nb(in))
          return false;

// If the valid data is written, return not-full (full_n) as true
  if (in.valid) {
    if (in.invert)
      full_n = output.write_nb(~in.data);
      full_n = output.write_nb(in.data);
  return full_n;