C++ Arbitrary Precision Integer Explicit Conversions

The ap_[u]int types support several explicit conversion functions which allow the value to be interpreted in different ways. The to_uint64() function will return a 64 bit unsigned long long with the same bits as the original ap_[u]int, zero extending and wrapping as necessary. Assigning an ap_[u]int wider than 64 bits to an unsigned long long would also wrap to match widths, without needing to call to_uint64(). The to_int64() function will return a 64 bit signed long long and will sign extend as necessary.

An arbitrary precision integer data type can be casted to an arbitrary precision fixed-point data type with the to_fixpt<I_W>() and to_ufixpt<I_W>() functions (returns ap_fixpt<W, I_W> and ap_ufixpt<W, I_W> types respectively), with the same bits as the original ap_[u]int<W>. For more on the ap_[u]fixpt template, please refer to the C++ Arbitrary Precision Fixed Point Library section.

An example demonstrating these functions is shown below.

#include "hls/ap_int.hpp"
#include <iostream>
#include <stdio.h>

using namespace hls;

    //...
    // zero extend 16 bit -32768 to 64 bit 32768
    unsigned long long A = ap_int<16>(-32768).to_uint64();
    std::cout << "A = " << A << std::endl;

    // wrap from 65 bit 2**64 + 1 to 64 bit 1
    unsigned long long B = ap_uint<65>("10000000000000001").to_uint64();
    std::cout << "B = " << B << std::endl;

    // interpret 8 bit uint as 8 bit ufixpt with four bits above decimal
    // by value 248 becomes 15.5 (== 248 / 2**4)
    ap_ufixpt<8, 4> C = ap_uint<8>(248).to_ufixpt<4>();
    std::cout << "C = " << C << std::endl;

    // interpret 4 bit int as 4 bit fixpt with leading bit 8 bits above decimal
    // by value -8 becomes -128 (== -8 * 2**4)
    ap_fixpt<4, 8> D = ap_int<4>(-8).to_fixpt<8>();
    std::cout << "D = " << D << std::endl;

    // interpret 6 bit int as 6 bit ufixpt with 6 bits above decimal
    // by value 8 becomes 8
    ap_ufixpt<6, 6> E = ap_int<6>(8).to_ufixpt<6>();
    std::cout << "E = " << E << std::endl;