int64x64.cc

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/*
 * Copyright (c) 2010 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 */
 
#include "int64x64.h"
 
#include "assert.h"
#include "log.h"
 
#include <iomanip> // showpos
#include <iostream>
#include <limits>
#include <sstream>
#include <stdint.h>
 
/**
 * \file
 * \ingroup highprec
 * Implementation of the streaming input and output operators for
 * the ns3::int64x64_t type.
 */
 
namespace ns3
{
 
// Note:  Logging in this file is largely avoided due to the
// number of calls that are made to these functions and the possibility
// of causing recursions leading to stack overflow
NS_LOG_COMPONENT_DEFINE_MASK("int64x64", LOG_PREFIX_TIME);
 
/**
 * \ingroup highprec
 * Print the high and low words of an int64x64 in hex, for debugging.
 *
 * \param [in] hi The high (integer) word.
 * \param [in] lo The low (fractional) work.
 */
#define HEXHILOW(hi, lo)                                                                           \
    std::hex << std::setfill('0') << std::right << " (0x" << std::setw(16) << hi << " "            \
             << std::setw(16) << lo << std::dec << std::setfill(' ') << std::left << ")"
 
/**
 * \internal
 * This algorithm is exact to the precision requested, up to the full
 * 64 decimal digits required to exactly represent a 64-bit fraction.
 *
 * Proper rounding turns out to be surprisingly hard.
 * In `y.xxxx5|6`, where the `|` marks follows the last output digit,
 * rounding the `5|6` to `6|` is straightforward.  However,
 * rounding `y.xxx99|6` should result in `y.xx100|`.  Notice the
 * effect of rounding percolates to higher digits.
 * We accumulate the output digits in a string, then carry out
 * the rounding in the string directly.
 */
std::ostream&
operator<<(std::ostream& os, const int64x64_t& value)
{
    const bool negative = (value < 0);
 
    uint64_t hi;
    int64x64_t low;
    if (value != int64x64_t(std::numeric_limits<int64_t>::min(), 0))
    {
        const int64x64_t absVal = (negative ? -value : value);
        hi = absVal.GetHigh();
        low = int64x64_t(0, absVal.GetLow());
    }
    else
    {
        hi = static_cast<uint64_t>(1) << 63;
    }
 
    // Save stream format flags
    auto precision = static_cast<std::size_t>(os.precision());
    std::ios_base::fmtflags ff = os.flags();
    const bool floatfield = os.flags() & std::ios_base::floatfield;
    os << std::setw(1) << std::noshowpos;
 
    os << std::right << (negative ? "-" : "+");
 
    std::ostringstream oss;
    oss << hi << "."; // collect the digits here so we can round properly
 
    std::size_t places = 0; // Number of decimal places printed so far
    bool more = true;       // Should we print more digits?
 
    NS_LOG_LOGIC(std::endl
                 << (floatfield ? " f" : "  ") << "[" << precision << "] " << hi << ". "
                 << HEXHILOW(hi, low.GetLow()));
 
    int64_t digit;
    do
    {
        low *= 10;
        digit = low.GetHigh();
        NS_ASSERT_MSG((0 <= digit) && (digit <= 9),
                      "digit " << digit << " out of range [0,9] "
                               << " streaming out " << HEXHILOW(value.GetHigh(), value.GetLow()));
        low -= digit;
 
        oss << std::setw(1) << digit;
 
        ++places;
        if (floatfield)
        {
            more = places < precision;
        }
        else // default
        {
            // Full resolution is 20 decimal digits
            more = low.GetLow() && (places < 20);
        }
 
        NS_LOG_LOGIC((more ? "+" : " ") << (floatfield ? "f" : " ") << "[" << places << "] "
                                        << digit << HEXHILOW(low.GetHigh(), low.GetLow())
                                        << std::dec << std::setfill(' ') << std::left);
 
    } while (more);
 
    // Check if we need to round the last printed digit,
    // based on the first unprinted digit
    std::string digits = oss.str();
    low *= 10;
    int64_t nextDigit = low.GetHigh();
    if ((nextDigit > 5) || ((nextDigit == 5) && (digit % 2 == 1)))
    {
        // Walk backwards with the carry
        bool carry = true;
        for (std::string::reverse_iterator rit = digits.rbegin(); rit != digits.rend(); ++rit)
        {
            if (*rit == '.') // Skip over the decimal point
            {
                continue;
            }
 
            ++(*rit);        // Add the carry
            if (*rit <= '9') // Relies on character order...
            {
                carry = false;
                break; // Carry complete
            }
            else
            {
                *rit = '0'; // Continue carry to next higher digit
            }
        }
        if (carry) // If we still have a carry...
        {
            digits.insert(digits.begin(), '1');
        }
    }
    os << digits;
 
    os.flags(ff); // Restore stream flags
    return os;
}
 
/**
 * \ingroup highprec
 * Read the integer portion of a number from a string containing
 * just the integral digits (no decimal point or fractional part).
 *
 * \param [in] str The string representation of the integral part
 *             of a number, with no fractional part or decimal point.
 * \returns    The integer.
 */
static uint64_t
ReadHiDigits(std::string str)
{
    const char* buf = str.c_str();
    uint64_t retval = 0;
    while (*buf != 0)
    {
        retval *= 10;
        retval += *buf - '0';
        buf++;
    }
    return retval;
}
 
/**
 * \ingroup highprec
 * Read the fractional part of a number from a string containing
 * just the decimal digits of the fractional part (no integral part
 * or decimal point).
 *
 * \param [in] str The string representation of the fractional part
 *             of a number, without integral part or decimal point.
 * \returns    The decimal portion of the input number.
 */
static uint64_t
ReadLoDigits(std::string str)
{
    int64x64_t low;
    const int64x64_t round(0, 5); // Round last place in division
 
    for (std::string::const_reverse_iterator rit = str.rbegin(); rit != str.rend(); ++rit)
    {
        int digit = *rit - '0';
        NS_ASSERT_MSG((0 <= digit) && (digit <= 9),
                      "digit " << digit << " out of range [0,9]"
                               << " streaming in low digits \"" << str << "\"");
        low = (low + digit + round) / 10;
    }
 
    return low.GetLow();
}
 
std::istream&
operator>>(std::istream& is, int64x64_t& value)
{
    std::string str;
 
    is >> str;
    bool negative;
    // skip heading spaces
    std::string::size_type cur;
    cur = str.find_first_not_of(' ');
    std::string::size_type next;
    // first, remove the sign.
    next = str.find('-', cur);
    if (next != std::string::npos)
    {
        negative = true;
        next++;
    }
    else
    {
        next = str.find('+', cur);
        if (next != std::string::npos)
        {
            next++;
        }
        else
        {
            next = cur;
        }
        negative = false;
    }
    cur = next;
    int64_t hi;
    uint64_t lo;
    next = str.find('.', cur);
    if (next != std::string::npos)
    {
        hi = ReadHiDigits(str.substr(cur, next - cur));
        lo = ReadLoDigits(str.substr(next + 1, str.size() - (next + 1)));
    }
    else if (cur != std::string::npos)
    {
        hi = ReadHiDigits(str.substr(cur, str.size() - cur));
        lo = 0;
    }
    else
    {
        hi = 0;
        lo = 0;
    }
 
    value = int64x64_t(hi, lo);
    value = negative ? -value : value;
 
    return is;
}
 
} // namespace ns3