update.cc

一个mips虚拟机非常好代码,使用C++来编写的,希望大家多学学,

#include <inttypes.hh>
#include "rtc.hh"


// Returns 1 if y is a leap year, 0 otherwise. Taken directly from the public
// domain code in 4.4BSD-Lite2.

inline bool
is_leap(int y)
{
    return ((y % 4) == 0 && ((y % 100) != 0 || (y % 400) == 0));
}


// Update the SRAM registers using the current value of the clock.

void
MT48Tx2::update_read(Clock *clock)
{
    UInt8 month_length[2][13] = {
	{ 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
	{ 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
    };

    ClockValue now, seconds, minutes, hour, day;
    ClockValue weekday, date,  month, year;

    now = clock->nanoseconds(*clock) - initial_time;

    seconds = initial_seconds + (now     / 1000 / 1000 / 1000);
    minutes = initial_minutes + (seconds / 60);
    hour    = initial_hour    + (minutes / 60);
    weekday = initial_weekday + (hour    / 24);

    seconds %= 60;
    minutes %= 60;
    hour    %= 24;

    // The rest is a legendary mess.
    date  = initial_date;
    month = initial_month;
    year  = initial_year;
    for (day = hour / 24; day; --day) {
	if (++date > month_length[is_leap(year)][month]) {
	    date = 1;
	    if (++month > 12) {
		month = 1;
		if (++year > 99) {
		    year = 0;
		}
	    }
	}
    }

    data[SECONDS] = ((seconds / 10) << 4) + seconds % 10;
    data[MINUTES] = ((minutes / 10) << 4) + minutes % 10;
    data[HOUR]    = ((hour    / 10) << 4) + hour    % 10;
    data[WEEKDAY] = (weekday - 1) % 7 + 1;
    data[DATE]    = ((date    / 10) << 4) + date    % 10;
    data[MONTH]   = ((month   / 10) << 4) + month   % 10;
    data[YEAR]    = ((year    / 10) << 4) + year    % 10;
}


// Update the timer based on the current values of time registers.  This is
// done by storing the start time and the corresponding wall time in
// nanoseconds, from which update_read() can compute the current time on
// request.

void
MT48Tx2::update_write(Clock *clock)
{
    // Wall time.
    initial_time = clock->nanoseconds(*clock);
    // Start time.
    initial_seconds = bits((UInt8)data[SECONDS], 3, 0)
	+ bits((UInt8)data[SECONDS], 6, 4) * 10;
    initial_minutes = bits((UInt8)data[MINUTES], 3, 0)
	+ bits((UInt8)data[SECONDS], 6, 4) * 10;
    initial_hour = bits((UInt8)data[HOUR], 3, 0)
	+ bits((UInt8)data[SECONDS], 5, 4) * 10;
    initial_weekday = bits((UInt8)data[WEEKDAY], 2, 0);
    initial_date = bits((UInt8)data[DATE], 3, 0)
	+ bits((UInt8)data[DATE], 5, 4) * 10;
    initial_month = bits((UInt8)data[MONTH], 3, 0)
	+ bits((UInt8)data[MONTH], 4, 4) * 10;
    initial_year = bits((UInt8)data[YEAR], 3, 0)
	+ bits((UInt8)data[YEAR], 7, 4) * 10;
}