Tasmota/lib/rc-switch-2.6.2.13/RCSwitch.cpp

704 lines
22 KiB
C++

/*
RCSwitch - Arduino libary for remote control outlet switches
Copyright (c) 2011 Suat Özgür. All right reserved.
Contributors:
- Andre Koehler / info(at)tomate-online(dot)de
- Gordeev Andrey Vladimirovich / gordeev(at)openpyro(dot)com
- Skineffect / http://forum.ardumote.com/viewtopic.php?f=2&t=46
- Dominik Fischer / dom_fischer(at)web(dot)de
- Frank Oltmanns / <first name>.<last name>(at)gmail(dot)com
- Andreas Steinel / A.<lastname>(at)gmail(dot)com
- Max Horn / max(at)quendi(dot)de
- Robert ter Vehn / <first name>.<last name>(at)gmail(dot)com
- Johann Richard / <first name>.<last name>(at)gmail(dot)com
- Vlad Gheorghe / <first name>.<last name>(at)gmail(dot)com https://github.com/vgheo
Project home: https://github.com/sui77/rc-switch/
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "RCSwitch.h"
#ifdef RaspberryPi
// PROGMEM and _P functions are for AVR based microprocessors,
// so we must normalize these for the ARM processor:
#define PROGMEM
#define memcpy_P(dest, src, num) memcpy((dest), (src), (num))
#endif
#if defined(ESP8266) || defined(ESP32)
// interrupt handler and related code must be in RAM on ESP8266,
// according to issue #46.
#define RECEIVE_ATTR ICACHE_RAM_ATTR
#else
#define RECEIVE_ATTR
#endif
/* Format for protocol definitions:
* {pulselength, Sync bit, "0" bit, "1" bit}
*
* pulselength: pulse length in microseconds, e.g. 350
* Sync bit: {1, 31} means 1 high pulse and 31 low pulses
* (perceived as a 31*pulselength long pulse, total length of sync bit is
* 32*pulselength microseconds), i.e:
* _
* | |_______________________________ (don't count the vertical bars)
* "0" bit: waveform for a data bit of value "0", {1, 3} means 1 high pulse
* and 3 low pulses, total length (1+3)*pulselength, i.e:
* _
* | |___
* "1" bit: waveform for a data bit of value "1", e.g. {3,1}:
* ___
* | |_
*
* These are combined to form Tri-State bits when sending or receiving codes.
*/
#if defined(ESP8266) || defined(ESP32)
static const RCSwitch::Protocol proto[] = {
#else
static const RCSwitch::Protocol PROGMEM proto[] = {
#endif
{ 350, { 1, 31 }, { 1, 3 }, { 3, 1 }, false }, // protocol 1
{ 650, { 1, 10 }, { 1, 2 }, { 2, 1 }, false }, // protocol 2
{ 100, { 30, 71 }, { 4, 11 }, { 9, 6 }, false }, // protocol 3
{ 380, { 1, 6 }, { 1, 3 }, { 3, 1 }, false }, // protocol 4
{ 500, { 6, 14 }, { 1, 2 }, { 2, 1 }, false }, // protocol 5
{ 450, { 23, 1 }, { 1, 2 }, { 2, 1 }, true }, // protocol 6 (HT6P20B)
{ 150, { 2, 62 }, { 1, 6 }, { 6, 1 }, false }, // protocol 7 (HS2303-PT, i. e. used in AUKEY Remote)
{ 200, { 3, 130}, { 7, 16 }, { 3, 16}, false}, // protocol 8 Conrad RS-200 RX
{ 200, { 130, 7 }, { 16, 7 }, { 16, 3 }, true} // protocol 9 Conrad RS-200 TX
};
enum {
numProto = sizeof(proto) / sizeof(proto[0])
};
#if not defined( RCSwitchDisableReceiving )
volatile unsigned long RCSwitch::nReceivedValue = 0;
volatile unsigned int RCSwitch::nReceivedBitlength = 0;
volatile unsigned int RCSwitch::nReceivedDelay = 0;
volatile unsigned int RCSwitch::nReceivedProtocol = 0;
int RCSwitch::nReceiveTolerance = 60;
const unsigned int RCSwitch::nSeparationLimit = 4300;
// separationLimit: minimum microseconds between received codes, closer codes are ignored.
// according to discussion on issue #14 it might be more suitable to set the separation
// limit to the same time as the 'low' part of the sync signal for the current protocol.
unsigned int RCSwitch::timings[RCSWITCH_MAX_CHANGES];
#endif
RCSwitch::RCSwitch() {
this->nTransmitterPin = -1;
this->setRepeatTransmit(10);
this->setProtocol(1);
#if not defined( RCSwitchDisableReceiving )
this->nReceiverInterrupt = -1;
this->setReceiveTolerance(60);
RCSwitch::nReceivedValue = 0;
#endif
}
/**
* Sets the protocol to send.
*/
void RCSwitch::setProtocol(Protocol protocol) {
this->protocol = protocol;
}
/**
* Sets the protocol to send, from a list of predefined protocols
*/
void RCSwitch::setProtocol(int nProtocol) {
if (nProtocol < 1 || nProtocol > numProto) {
nProtocol = 1; // TODO: trigger an error, e.g. "bad protocol" ???
}
#if defined(ESP8266) || defined(ESP32)
this->protocol = proto[nProtocol-1];
#else
memcpy_P(&this->protocol, &proto[nProtocol-1], sizeof(Protocol));
#endif
}
/**
* Sets the protocol to send with pulse length in microseconds.
*/
void RCSwitch::setProtocol(int nProtocol, int nPulseLength) {
setProtocol(nProtocol);
this->setPulseLength(nPulseLength);
}
/**
* Sets pulse length in microseconds
*/
void RCSwitch::setPulseLength(int nPulseLength) {
this->protocol.pulseLength = nPulseLength;
}
/**
* Sets Repeat Transmits
*/
void RCSwitch::setRepeatTransmit(int nRepeatTransmit) {
this->nRepeatTransmit = nRepeatTransmit;
}
/**
* Set Receiving Tolerance
*/
#if not defined( RCSwitchDisableReceiving )
void RCSwitch::setReceiveTolerance(int nPercent) {
RCSwitch::nReceiveTolerance = nPercent;
}
#endif
/**
* Enable transmissions
*
* @param nTransmitterPin Arduino Pin to which the sender is connected to
*/
void RCSwitch::enableTransmit(int nTransmitterPin) {
this->nTransmitterPin = nTransmitterPin;
pinMode(this->nTransmitterPin, OUTPUT);
}
/**
* Disable transmissions
*/
void RCSwitch::disableTransmit() {
this->nTransmitterPin = -1;
}
/**
* Switch a remote switch on (Type D REV)
*
* @param sGroup Code of the switch group (A,B,C,D)
* @param nDevice Number of the switch itself (1..3)
*/
void RCSwitch::switchOn(char sGroup, int nDevice) {
this->sendTriState( this->getCodeWordD(sGroup, nDevice, true) );
}
/**
* Switch a remote switch off (Type D REV)
*
* @param sGroup Code of the switch group (A,B,C,D)
* @param nDevice Number of the switch itself (1..3)
*/
void RCSwitch::switchOff(char sGroup, int nDevice) {
this->sendTriState( this->getCodeWordD(sGroup, nDevice, false) );
}
/**
* Switch a remote switch on (Type C Intertechno)
*
* @param sFamily Familycode (a..f)
* @param nGroup Number of group (1..4)
* @param nDevice Number of device (1..4)
*/
void RCSwitch::switchOn(char sFamily, int nGroup, int nDevice) {
this->sendTriState( this->getCodeWordC(sFamily, nGroup, nDevice, true) );
}
/**
* Switch a remote switch off (Type C Intertechno)
*
* @param sFamily Familycode (a..f)
* @param nGroup Number of group (1..4)
* @param nDevice Number of device (1..4)
*/
void RCSwitch::switchOff(char sFamily, int nGroup, int nDevice) {
this->sendTriState( this->getCodeWordC(sFamily, nGroup, nDevice, false) );
}
/**
* Switch a remote switch on (Type B with two rotary/sliding switches)
*
* @param nAddressCode Number of the switch group (1..4)
* @param nChannelCode Number of the switch itself (1..4)
*/
void RCSwitch::switchOn(int nAddressCode, int nChannelCode) {
this->sendTriState( this->getCodeWordB(nAddressCode, nChannelCode, true) );
}
/**
* Switch a remote switch off (Type B with two rotary/sliding switches)
*
* @param nAddressCode Number of the switch group (1..4)
* @param nChannelCode Number of the switch itself (1..4)
*/
void RCSwitch::switchOff(int nAddressCode, int nChannelCode) {
this->sendTriState( this->getCodeWordB(nAddressCode, nChannelCode, false) );
}
/**
* Deprecated, use switchOn(const char* sGroup, const char* sDevice) instead!
* Switch a remote switch on (Type A with 10 pole DIP switches)
*
* @param sGroup Code of the switch group (refers to DIP switches 1..5 where "1" = on and "0" = off, if all DIP switches are on it's "11111")
* @param nChannelCode Number of the switch itself (1..5)
*/
void RCSwitch::switchOn(const char* sGroup, int nChannel) {
const char* code[6] = { "00000", "10000", "01000", "00100", "00010", "00001" };
this->switchOn(sGroup, code[nChannel]);
}
/**
* Deprecated, use switchOff(const char* sGroup, const char* sDevice) instead!
* Switch a remote switch off (Type A with 10 pole DIP switches)
*
* @param sGroup Code of the switch group (refers to DIP switches 1..5 where "1" = on and "0" = off, if all DIP switches are on it's "11111")
* @param nChannelCode Number of the switch itself (1..5)
*/
void RCSwitch::switchOff(const char* sGroup, int nChannel) {
const char* code[6] = { "00000", "10000", "01000", "00100", "00010", "00001" };
this->switchOff(sGroup, code[nChannel]);
}
/**
* Switch a remote switch on (Type A with 10 pole DIP switches)
*
* @param sGroup Code of the switch group (refers to DIP switches 1..5 where "1" = on and "0" = off, if all DIP switches are on it's "11111")
* @param sDevice Code of the switch device (refers to DIP switches 6..10 (A..E) where "1" = on and "0" = off, if all DIP switches are on it's "11111")
*/
void RCSwitch::switchOn(const char* sGroup, const char* sDevice) {
this->sendTriState( this->getCodeWordA(sGroup, sDevice, true) );
}
/**
* Switch a remote switch off (Type A with 10 pole DIP switches)
*
* @param sGroup Code of the switch group (refers to DIP switches 1..5 where "1" = on and "0" = off, if all DIP switches are on it's "11111")
* @param sDevice Code of the switch device (refers to DIP switches 6..10 (A..E) where "1" = on and "0" = off, if all DIP switches are on it's "11111")
*/
void RCSwitch::switchOff(const char* sGroup, const char* sDevice) {
this->sendTriState( this->getCodeWordA(sGroup, sDevice, false) );
}
/**
* Returns a char[13], representing the code word to be send.
*
*/
char* RCSwitch::getCodeWordA(const char* sGroup, const char* sDevice, bool bStatus) {
static char sReturn[13];
int nReturnPos = 0;
for (int i = 0; i < 5; i++) {
sReturn[nReturnPos++] = (sGroup[i] == '0') ? 'F' : '0';
}
for (int i = 0; i < 5; i++) {
sReturn[nReturnPos++] = (sDevice[i] == '0') ? 'F' : '0';
}
sReturn[nReturnPos++] = bStatus ? '0' : 'F';
sReturn[nReturnPos++] = bStatus ? 'F' : '0';
sReturn[nReturnPos] = '\0';
return sReturn;
}
/**
* Encoding for type B switches with two rotary/sliding switches.
*
* The code word is a tristate word and with following bit pattern:
*
* +-----------------------------+-----------------------------+----------+------------+
* | 4 bits address | 4 bits address | 3 bits | 1 bit |
* | switch group | switch number | not used | on / off |
* | 1=0FFF 2=F0FF 3=FF0F 4=FFF0 | 1=0FFF 2=F0FF 3=FF0F 4=FFF0 | FFF | on=F off=0 |
* +-----------------------------+-----------------------------+----------+------------+
*
* @param nAddressCode Number of the switch group (1..4)
* @param nChannelCode Number of the switch itself (1..4)
* @param bStatus Whether to switch on (true) or off (false)
*
* @return char[13], representing a tristate code word of length 12
*/
char* RCSwitch::getCodeWordB(int nAddressCode, int nChannelCode, bool bStatus) {
static char sReturn[13];
int nReturnPos = 0;
if (nAddressCode < 1 || nAddressCode > 4 || nChannelCode < 1 || nChannelCode > 4) {
return 0;
}
for (int i = 1; i <= 4; i++) {
sReturn[nReturnPos++] = (nAddressCode == i) ? '0' : 'F';
}
for (int i = 1; i <= 4; i++) {
sReturn[nReturnPos++] = (nChannelCode == i) ? '0' : 'F';
}
sReturn[nReturnPos++] = 'F';
sReturn[nReturnPos++] = 'F';
sReturn[nReturnPos++] = 'F';
sReturn[nReturnPos++] = bStatus ? 'F' : '0';
sReturn[nReturnPos] = '\0';
return sReturn;
}
/**
* Like getCodeWord (Type C = Intertechno)
*/
char* RCSwitch::getCodeWordC(char sFamily, int nGroup, int nDevice, bool bStatus) {
static char sReturn[13];
int nReturnPos = 0;
int nFamily = (int)sFamily - 'a';
if ( nFamily < 0 || nFamily > 15 || nGroup < 1 || nGroup > 4 || nDevice < 1 || nDevice > 4) {
return 0;
}
// encode the family into four bits
sReturn[nReturnPos++] = (nFamily & 1) ? 'F' : '0';
sReturn[nReturnPos++] = (nFamily & 2) ? 'F' : '0';
sReturn[nReturnPos++] = (nFamily & 4) ? 'F' : '0';
sReturn[nReturnPos++] = (nFamily & 8) ? 'F' : '0';
// encode the device and group
sReturn[nReturnPos++] = ((nDevice-1) & 1) ? 'F' : '0';
sReturn[nReturnPos++] = ((nDevice-1) & 2) ? 'F' : '0';
sReturn[nReturnPos++] = ((nGroup-1) & 1) ? 'F' : '0';
sReturn[nReturnPos++] = ((nGroup-1) & 2) ? 'F' : '0';
// encode the status code
sReturn[nReturnPos++] = '0';
sReturn[nReturnPos++] = 'F';
sReturn[nReturnPos++] = 'F';
sReturn[nReturnPos++] = bStatus ? 'F' : '0';
sReturn[nReturnPos] = '\0';
return sReturn;
}
/**
* Encoding for the REV Switch Type
*
* The code word is a tristate word and with following bit pattern:
*
* +-----------------------------+-------------------+----------+--------------+
* | 4 bits address | 3 bits address | 3 bits | 2 bits |
* | switch group | device number | not used | on / off |
* | A=1FFF B=F1FF C=FF1F D=FFF1 | 1=0FF 2=F0F 3=FF0 | 000 | on=10 off=01 |
* +-----------------------------+-------------------+----------+--------------+
*
* Source: http://www.the-intruder.net/funksteckdosen-von-rev-uber-arduino-ansteuern/
*
* @param sGroup Name of the switch group (A..D, resp. a..d)
* @param nDevice Number of the switch itself (1..3)
* @param bStatus Whether to switch on (true) or off (false)
*
* @return char[13], representing a tristate code word of length 12
*/
char* RCSwitch::getCodeWordD(char sGroup, int nDevice, bool bStatus) {
static char sReturn[13];
int nReturnPos = 0;
// sGroup must be one of the letters in "abcdABCD"
int nGroup = (sGroup >= 'a') ? (int)sGroup - 'a' : (int)sGroup - 'A';
if ( nGroup < 0 || nGroup > 3 || nDevice < 1 || nDevice > 3) {
return 0;
}
for (int i = 0; i < 4; i++) {
sReturn[nReturnPos++] = (nGroup == i) ? '1' : 'F';
}
for (int i = 1; i <= 3; i++) {
sReturn[nReturnPos++] = (nDevice == i) ? '1' : 'F';
}
sReturn[nReturnPos++] = '0';
sReturn[nReturnPos++] = '0';
sReturn[nReturnPos++] = '0';
sReturn[nReturnPos++] = bStatus ? '1' : '0';
sReturn[nReturnPos++] = bStatus ? '0' : '1';
sReturn[nReturnPos] = '\0';
return sReturn;
}
/**
* @param sCodeWord a tristate code word consisting of the letter 0, 1, F
*/
void RCSwitch::sendTriState(const char* sCodeWord) {
// turn the tristate code word into the corresponding bit pattern, then send it
unsigned long code = 0;
unsigned int length = 0;
for (const char* p = sCodeWord; *p; p++) {
code <<= 2L;
switch (*p) {
case '0':
// bit pattern 00
break;
case 'F':
// bit pattern 01
code |= 1L;
break;
case '1':
// bit pattern 11
code |= 3L;
break;
}
length += 2;
}
this->send(code, length);
}
/**
* @param sCodeWord a binary code word consisting of the letter 0, 1
*/
void RCSwitch::send(const char* sCodeWord) {
// turn the tristate code word into the corresponding bit pattern, then send it
unsigned long code = 0;
unsigned int length = 0;
for (const char* p = sCodeWord; *p; p++) {
code <<= 1L;
if (*p != '0')
code |= 1L;
length++;
}
this->send(code, length);
}
/**
* Transmit the first 'length' bits of the integer 'code'. The
* bits are sent from MSB to LSB, i.e., first the bit at position length-1,
* then the bit at position length-2, and so on, till finally the bit at position 0.
*/
void RCSwitch::send(unsigned long code, unsigned int length) {
if (this->nTransmitterPin == -1)
return;
#if not defined( RCSwitchDisableReceiving )
// make sure the receiver is disabled while we transmit
int nReceiverInterrupt_backup = nReceiverInterrupt;
if (nReceiverInterrupt_backup != -1) {
this->disableReceive();
}
#endif
for (int nRepeat = 0; nRepeat < nRepeatTransmit; nRepeat++) {
for (int i = length-1; i >= 0; i--) {
if (code & (1L << i))
this->transmit(protocol.one);
else
this->transmit(protocol.zero);
}
this->transmit(protocol.syncFactor);
}
// Disable transmit after sending (i.e., for inverted protocols)
digitalWrite(this->nTransmitterPin, LOW);
#if not defined( RCSwitchDisableReceiving )
// enable receiver again if we just disabled it
if (nReceiverInterrupt_backup != -1) {
this->enableReceive(nReceiverInterrupt_backup);
}
#endif
}
/**
* Transmit a single high-low pulse.
*/
void RCSwitch::transmit(HighLow pulses) {
uint8_t firstLogicLevel = (this->protocol.invertedSignal) ? LOW : HIGH;
uint8_t secondLogicLevel = (this->protocol.invertedSignal) ? HIGH : LOW;
digitalWrite(this->nTransmitterPin, firstLogicLevel);
delayMicroseconds( this->protocol.pulseLength * pulses.high);
digitalWrite(this->nTransmitterPin, secondLogicLevel);
delayMicroseconds( this->protocol.pulseLength * pulses.low);
}
#if not defined( RCSwitchDisableReceiving )
/**
* Enable receiving data
*/
void RCSwitch::enableReceive(int interrupt) {
this->nReceiverInterrupt = interrupt;
this->enableReceive();
}
void RCSwitch::enableReceive() {
if (this->nReceiverInterrupt != -1) {
RCSwitch::nReceivedValue = 0;
RCSwitch::nReceivedBitlength = 0;
#if defined(RaspberryPi) // Raspberry Pi
wiringPiISR(this->nReceiverInterrupt, INT_EDGE_BOTH, &handleInterrupt);
#else // Arduino
attachInterrupt(this->nReceiverInterrupt, handleInterrupt, CHANGE);
#endif
}
}
/**
* Disable receiving data
*/
void RCSwitch::disableReceive() {
#if not defined(RaspberryPi) // Arduino
detachInterrupt(this->nReceiverInterrupt);
#endif // For Raspberry Pi (wiringPi) you can't unregister the ISR
this->nReceiverInterrupt = -1;
}
bool RCSwitch::available() {
return RCSwitch::nReceivedValue != 0;
}
void RCSwitch::resetAvailable() {
RCSwitch::nReceivedValue = 0;
}
unsigned long RCSwitch::getReceivedValue() {
return RCSwitch::nReceivedValue;
}
unsigned int RCSwitch::getReceivedBitlength() {
return RCSwitch::nReceivedBitlength;
}
unsigned int RCSwitch::getReceivedDelay() {
return RCSwitch::nReceivedDelay;
}
unsigned int RCSwitch::getReceivedProtocol() {
return RCSwitch::nReceivedProtocol;
}
unsigned int* RCSwitch::getReceivedRawdata() {
return RCSwitch::timings;
}
/* helper function for the receiveProtocol method */
static inline unsigned int diff(int A, int B) {
return abs(A - B);
}
/**
*
*/
bool RECEIVE_ATTR RCSwitch::receiveProtocol(const int p, unsigned int changeCount) {
#if defined(ESP8266) || defined(ESP32)
const Protocol &pro = proto[p-1];
#else
Protocol pro;
memcpy_P(&pro, &proto[p-1], sizeof(Protocol));
#endif
unsigned long code = 0;
//Assuming the longer pulse length is the pulse captured in timings[0]
const unsigned int syncLengthInPulses = ((pro.syncFactor.low) > (pro.syncFactor.high)) ? (pro.syncFactor.low) : (pro.syncFactor.high);
const unsigned int delay = RCSwitch::timings[0] / syncLengthInPulses;
const unsigned int delayTolerance = delay * RCSwitch::nReceiveTolerance / 100;
/* For protocols that start low, the sync period looks like
* _________
* _____________| |XXXXXXXXXXXX|
*
* |--1st dur--|-2nd dur-|-Start data-|
*
* The 3rd saved duration starts the data.
*
* For protocols that start high, the sync period looks like
*
* ______________
* | |____________|XXXXXXXXXXXXX|
*
* |-filtered out-|--1st dur--|--Start data--|
*
* The 2nd saved duration starts the data
*/
const unsigned int firstDataTiming = (pro.invertedSignal) ? (2) : (1);
for (unsigned int i = firstDataTiming; i < changeCount - 1; i += 2) {
code <<= 1;
if (diff(RCSwitch::timings[i], delay * pro.zero.high) < delayTolerance &&
diff(RCSwitch::timings[i + 1], delay * pro.zero.low) < delayTolerance) {
// zero
} else if (diff(RCSwitch::timings[i], delay * pro.one.high) < delayTolerance &&
diff(RCSwitch::timings[i + 1], delay * pro.one.low) < delayTolerance) {
// one
code |= 1;
} else {
// Failed
return false;
}
}
if (changeCount > 7) { // ignore very short transmissions: no device sends them, so this must be noise
RCSwitch::nReceivedValue = code;
RCSwitch::nReceivedBitlength = (changeCount - 1) / 2;
RCSwitch::nReceivedDelay = delay;
RCSwitch::nReceivedProtocol = p;
return true;
}
return false;
}
void RECEIVE_ATTR RCSwitch::handleInterrupt() {
static unsigned int changeCount = 0;
static unsigned long lastTime = 0;
static unsigned int repeatCount = 0;
const long time = micros();
const unsigned int duration = time - lastTime;
if (duration > RCSwitch::nSeparationLimit) {
// A long stretch without signal level change occurred. This could
// be the gap between two transmission.
if ((repeatCount==0) || (diff(duration, RCSwitch::timings[0]) < 200)) {
// This long signal is close in length to the long signal which
// started the previously recorded timings; this suggests that
// it may indeed by a a gap between two transmissions (we assume
// here that a sender will send the signal multiple times,
// with roughly the same gap between them).
repeatCount++;
if (repeatCount == 2) {
for(unsigned int i = 1; i <= numProto; i++) {
if (receiveProtocol(i, changeCount)) {
// receive succeeded for protocol i
break;
}
}
repeatCount = 0;
}
}
changeCount = 0;
}
// detect overflow
if (changeCount >= RCSWITCH_MAX_CHANGES) {
changeCount = 0;
repeatCount = 0;
}
RCSwitch::timings[changeCount++] = duration;
lastTime = time;
}
#endif