(implementing suggestion #94)

[proxmark3-svn] / common / lfdemod.c

//-----------------------------------------------------------------------------
// Copyright (C) 2014
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Low frequency demod/decode commands
//-----------------------------------------------------------------------------

#include <stdlib.h>
#include <string.h>
#include "lfdemod.h"
uint8_t justNoise(uint8_t *BitStream, size_t size)
{
	static const uint8_t THRESHOLD = 123;
	//test samples are not just noise
	uint8_t justNoise1 = 1;
	for(size_t idx=0; idx < size && justNoise1 ;idx++){
		justNoise1 = BitStream[idx] < THRESHOLD;
	}
	return justNoise1;
}

//by marshmellow
//get high and low values of a wave with passed in fuzz factor. also return noise test = 1 for passed or 0 for only noise
int getHiLo(uint8_t *BitStream, size_t size, int *high, int *low, uint8_t fuzzHi, uint8_t fuzzLo)
{
	*high=0;
	*low=255;
	// get high and low thresholds 
	for (size_t i=0; i < size; i++){
		if (BitStream[i] > *high) *high = BitStream[i];
		if (BitStream[i] < *low) *low = BitStream[i];
	}
	if (*high < 123) return -1; // just noise
	*high = ((*high-128)*fuzzHi + 12800)/100;
	*low = ((*low-128)*fuzzLo + 12800)/100;
	return 1;
}

// by marshmellow
// pass bits to be tested in bits, length bits passed in bitLen, and parity type (even=0 | odd=1) in pType
// returns 1 if passed
uint8_t parityTest(uint32_t bits, uint8_t bitLen, uint8_t pType)
{
	uint8_t ans = 0;
	for (uint8_t i = 0; i < bitLen; i++){
		ans ^= ((bits >> i) & 1);
	}
	//PrintAndLog("DEBUG: ans: %d, ptype: %d",ans,pType);
	return (ans == pType);
}

//by marshmellow
//search for given preamble in given BitStream and return success=1 or fail=0 and startIndex and length
uint8_t preambleSearch(uint8_t *BitStream, uint8_t *preamble, size_t pLen, size_t *size, size_t *startIdx)
{
	uint8_t foundCnt=0;
	for (int idx=0; idx < *size - pLen; idx++){
		if (memcmp(BitStream+idx, preamble, pLen) == 0){
			//first index found
			foundCnt++;
			if (foundCnt == 1){
				*startIdx = idx;
			}
			if (foundCnt == 2){
				*size = idx - *startIdx;
				return 1;
			}
		}
	}
	return 0;
}

//by marshmellow
//takes 1s and 0s and searches for EM410x format - output EM ID
uint8_t Em410xDecode(uint8_t *BitStream, size_t *size, size_t *startIdx, uint32_t *hi, uint64_t *lo)
{
	//no arguments needed - built this way in case we want this to be a direct call from "data " cmds in the future
	//  otherwise could be a void with no arguments
	//set defaults
	uint32_t i = 0;
	if (BitStream[1]>1) return 0;  //allow only 1s and 0s

	// 111111111 bit pattern represent start of frame
	//  include 0 in front to help get start pos
	uint8_t preamble[] = {0,1,1,1,1,1,1,1,1,1};
	uint32_t idx = 0;
	uint32_t parityBits = 0;
	uint8_t errChk = 0;
	uint8_t FmtLen = 10;
	*startIdx = 0;
	errChk = preambleSearch(BitStream, preamble, sizeof(preamble), size, startIdx);
	if (errChk == 0 || *size < 64) return 0;
	if (*size > 64) FmtLen = 22;
	*startIdx += 1; //get rid of 0 from preamble
	idx = *startIdx + 9;
	for (i=0; i<FmtLen; i++){ //loop through 10 or 22 sets of 5 bits (50-10p = 40 bits or 88 bits)
		parityBits = bytebits_to_byte(BitStream+(i*5)+idx,5);
		//check even parity - quit if failed
		if (parityTest(parityBits, 5, 0) == 0) return 0;
		//set uint64 with ID from BitStream
		for (uint8_t ii=0; ii<4; ii++){
			*hi = (*hi << 1) | (*lo >> 63);
			*lo = (*lo << 1) | (BitStream[(i*5)+ii+idx]);
		}
	}
	if (errChk != 0) return 1;
	//skip last 5 bit parity test for simplicity.
	// *size = 64 | 128;
	return 0;
}

//by marshmellow
//demodulates strong heavily clipped samples
int cleanAskRawDemod(uint8_t *BinStream, size_t *size, int clk, int invert, int high, int low)
{
	size_t bitCnt=0, smplCnt=0, errCnt=0;
	uint8_t waveHigh = 0;
	for (size_t i=0; i < *size; i++){
		if (BinStream[i] >= high && waveHigh){
			smplCnt++;
		} else if (BinStream[i] <= low && !waveHigh){
			smplCnt++;
		} else { //transition
			if ((BinStream[i] >= high && !waveHigh) || (BinStream[i] <= low && waveHigh)){
				if (smplCnt > clk-(clk/4)-1) { //full clock
					if (smplCnt > clk + (clk/4)+1) { //too many samples
						errCnt++;
						BinStream[bitCnt++]=7;
					} else if (waveHigh) {
						BinStream[bitCnt++] = invert;
						BinStream[bitCnt++] = invert;
					} else if (!waveHigh) {
						BinStream[bitCnt++] = invert ^ 1;
						BinStream[bitCnt++] = invert ^ 1;
					}
					waveHigh ^= 1;  
					smplCnt = 0;
				} else if (smplCnt > (clk/2) - (clk/4)-1) {
					if (waveHigh) {
						BinStream[bitCnt++] = invert;
					} else if (!waveHigh) {
						BinStream[bitCnt++] = invert ^ 1;
					}
					waveHigh ^= 1;  
					smplCnt = 0;
				} else if (!bitCnt) {
					//first bit
					waveHigh = (BinStream[i] >= high);
					smplCnt = 1;
				} else {
					smplCnt++;
					//transition bit oops
				}
			} else { //haven't hit new high or new low yet
				smplCnt++;
			}
		}
	}
	*size = bitCnt;
	return errCnt;
}

//by marshmellow
void askAmp(uint8_t *BitStream, size_t size)
{
	for(size_t i = 1; i<size; i++){
		if (BitStream[i]-BitStream[i-1]>=30) //large jump up
			BitStream[i]=127;
		else if(BitStream[i]-BitStream[i-1]<=-20) //large jump down
			BitStream[i]=-127;
	}
	return;
}

//by marshmellow
//attempts to demodulate ask modulations, askType == 0 for ask/raw, askType==1 for ask/manchester
int askdemod(uint8_t *BinStream, size_t *size, int *clk, int *invert, int maxErr, uint8_t amp, uint8_t askType)
{
	if (*size==0) return -1;
	int start = DetectASKClock(BinStream, *size, clk, maxErr); //clock default
	if (*clk==0 || start < 0) return -3;
	if (*invert != 1) *invert = 0;
	if (amp==1) askAmp(BinStream, *size);

	uint8_t initLoopMax = 255;
	if (initLoopMax > *size) initLoopMax = *size;
	// Detect high and lows
	//25% clip in case highs and lows aren't clipped [marshmellow]
	int high, low;
	if (getHiLo(BinStream, initLoopMax, &high, &low, 75, 75) < 1) 
		return -2; //just noise

	size_t errCnt = 0;
	// if clean clipped waves detected run alternate demod
	if (DetectCleanAskWave(BinStream, *size, high, low)) {
		errCnt = cleanAskRawDemod(BinStream, size, *clk, *invert, high, low);
		if (askType) //askman
			return manrawdecode(BinStream, size, 0);	
		else //askraw
			return errCnt;
	}

	int lastBit;  //set first clock check - can go negative
	size_t i, bitnum = 0;     //output counter
	uint8_t midBit = 0;
	uint8_t tol = 0;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
	if (*clk <= 32) tol = 1;    //clock tolerance may not be needed anymore currently set to + or - 1 but could be increased for poor waves or removed entirely
	size_t MaxBits = 1024;
	lastBit = start - *clk;

	for (i = start; i < *size; ++i) {
		if (i-lastBit >= *clk-tol){
			if (BinStream[i] >= high) {
				BinStream[bitnum++] = *invert;
			} else if (BinStream[i] <= low) {
				BinStream[bitnum++] = *invert ^ 1;
			} else if (i-lastBit >= *clk+tol) {
				if (bitnum > 0) {
					BinStream[bitnum++]=7;
					errCnt++;						
				} 
			} else { //in tolerance - looking for peak
				continue;
			}
			midBit = 0;
			lastBit += *clk;
		} else if (i-lastBit >= (*clk/2-tol) && !midBit && !askType){
			if (BinStream[i] >= high) {
				BinStream[bitnum++] = *invert;
			} else if (BinStream[i] <= low) {
				BinStream[bitnum++] = *invert ^ 1;
			} else if (i-lastBit >= *clk/2+tol) {
				BinStream[bitnum] = BinStream[bitnum-1];
				bitnum++;
			} else { //in tolerance - looking for peak
				continue;
			}
			midBit = 1;
		}
		if (bitnum >= MaxBits) break;
	}
	*size = bitnum;
	return errCnt;
}

//by marshmellow
//take 10 and 01 and manchester decode
//run through 2 times and take least errCnt
int manrawdecode(uint8_t * BitStream, size_t *size, uint8_t invert)
{
	uint16_t bitnum=0, MaxBits = 512, errCnt = 0;
	size_t i, ii;
	uint16_t bestErr = 1000, bestRun = 0;
	if (*size < 16) return -1;
	//find correct start position [alignment]
	for (ii=0;ii<2;++ii){
		for (i=ii; i<*size-3; i+=2)
			if (BitStream[i]==BitStream[i+1])
				errCnt++;

		if (bestErr>errCnt){
			bestErr=errCnt;
			bestRun=ii;
		}
		errCnt=0;
	}
	//decode
	for (i=bestRun; i < *size-3; i+=2){
		if(BitStream[i] == 1 && (BitStream[i+1] == 0)){
			BitStream[bitnum++]=invert;
		} else if((BitStream[i] == 0) && BitStream[i+1] == 1){
			BitStream[bitnum++]=invert^1;
		} else {
			BitStream[bitnum++]=7;
		}
		if(bitnum>MaxBits) break;
	}
	*size=bitnum;
	return bestErr;
}

//by marshmellow
//encode binary data into binary manchester 
int ManchesterEncode(uint8_t *BitStream, size_t size)
{
	size_t modIdx=20000, i=0;
	if (size>modIdx) return -1;
	for (size_t idx=0; idx < size; idx++){
		BitStream[idx+modIdx++] = BitStream[idx];
		BitStream[idx+modIdx++] = BitStream[idx]^1;
	}
	for (; i<(size*2); i++){
		BitStream[i] = BitStream[i+20000];
	}
	return i;
}

//by marshmellow
//take 01 or 10 = 1 and 11 or 00 = 0
//check for phase errors - should never have 111 or 000 should be 01001011 or 10110100 for 1010
//decodes biphase or if inverted it is AKA conditional dephase encoding AKA differential manchester encoding
int BiphaseRawDecode(uint8_t *BitStream, size_t *size, int offset, int invert)
{
	uint16_t bitnum = 0;
	uint16_t errCnt = 0;
	size_t i = offset;
	uint16_t MaxBits=512;
	//if not enough samples - error
	if (*size < 51) return -1;
	//check for phase change faults - skip one sample if faulty
	uint8_t offsetA = 1, offsetB = 1;
	for (; i<48; i+=2){
		if (BitStream[i+1]==BitStream[i+2]) offsetA=0; 
		if (BitStream[i+2]==BitStream[i+3]) offsetB=0;					
	}
	if (!offsetA && offsetB) offset++;
	for (i=offset; i<*size-3; i+=2){
		//check for phase error
		if (BitStream[i+1]==BitStream[i+2]) {
			BitStream[bitnum++]=7;
			errCnt++;
		}
		if((BitStream[i]==1 && BitStream[i+1]==0) || (BitStream[i]==0 && BitStream[i+1]==1)){
			BitStream[bitnum++]=1^invert;
		} else if((BitStream[i]==0 && BitStream[i+1]==0) || (BitStream[i]==1 && BitStream[i+1]==1)){
			BitStream[bitnum++]=invert;
		} else {
			BitStream[bitnum++]=7;
			errCnt++;
		}
		if(bitnum>MaxBits) break;
	}
	*size=bitnum;
	return errCnt;
}

// by marshmellow
// demod gProxIIDemod 
// error returns as -x 
// success returns start position in BitStream
// BitStream must contain previously askrawdemod and biphasedemoded data
int gProxII_Demod(uint8_t BitStream[], size_t *size)
{
	size_t startIdx=0;
	uint8_t preamble[] = {1,1,1,1,1,0};

	uint8_t errChk = preambleSearch(BitStream, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -3; //preamble not found
	if (*size != 96) return -2; //should have found 96 bits
	//check first 6 spacer bits to verify format
	if (!BitStream[startIdx+5] && !BitStream[startIdx+10] && !BitStream[startIdx+15] && !BitStream[startIdx+20] && !BitStream[startIdx+25] && !BitStream[startIdx+30]){
		//confirmed proper separator bits found
		//return start position
		return (int) startIdx;
	}
	return -5;
}

//translate wave to 11111100000 (1 for each short wave 0 for each long wave)
size_t fsk_wave_demod(uint8_t * dest, size_t size, uint8_t fchigh, uint8_t fclow)
{
	size_t last_transition = 0;
	size_t idx = 1;
	//uint32_t maxVal=0;
	if (fchigh==0) fchigh=10;
	if (fclow==0) fclow=8;
	//set the threshold close to 0 (graph) or 128 std to avoid static
	uint8_t threshold_value = 123; 

	// sync to first lo-hi transition, and threshold

	// Need to threshold first sample

	if(dest[0] < threshold_value) dest[0] = 0;
	else dest[0] = 1;

	size_t numBits = 0;
	// count cycles between consecutive lo-hi transitions, there should be either 8 (fc/8)
	// or 10 (fc/10) cycles but in practice due to noise etc we may end up with with anywhere
	// between 7 to 11 cycles so fuzz it by treat anything <9 as 8 and anything else as 10
	for(idx = 1; idx < size; idx++) {
		// threshold current value

		if (dest[idx] < threshold_value) dest[idx] = 0;
		else dest[idx] = 1;

		// Check for 0->1 transition
		if (dest[idx-1] < dest[idx]) { // 0 -> 1 transition
			if ((idx-last_transition)<(fclow-2)){            //0-5 = garbage noise
				//do nothing with extra garbage
			} else if ((idx-last_transition) < (fchigh-1)) { //6-8 = 8 waves
				dest[numBits++]=1;
			} else if ((idx-last_transition) > (fchigh+1) && !numBits) { //12 + and first bit = garbage 
				//do nothing with beginning garbage
			} else {                                         //9+ = 10 waves
				dest[numBits++]=0;
			}
			last_transition = idx;
		}
	}
	return numBits; //Actually, it returns the number of bytes, but each byte represents a bit: 1 or 0
}

//translate 11111100000 to 10
size_t aggregate_bits(uint8_t *dest, size_t size, uint8_t rfLen,
		uint8_t invert, uint8_t fchigh, uint8_t fclow)
{
	uint8_t lastval=dest[0];
	size_t idx=0;
	size_t numBits=0;
	uint32_t n=1;
	for( idx=1; idx < size; idx++) {
		n++;
		if (dest[idx]==lastval) continue; 
		
		//if lastval was 1, we have a 1->0 crossing
		if (dest[idx-1]==1) {
			if (!numBits && n < rfLen/fclow) {
				n=0;
				lastval = dest[idx];
				continue;
			}
			n = (n * fclow + rfLen/2) / rfLen;
		} else {// 0->1 crossing 
			//test first bitsample too small
			if (!numBits && n < rfLen/fchigh) {
				n=0;
				lastval = dest[idx];
				continue;
			}
			n = (n * fchigh + rfLen/2) / rfLen; 
		}
		if (n == 0) n = 1;

		memset(dest+numBits, dest[idx-1]^invert , n);
		numBits += n;
		n=0;
		lastval=dest[idx];
	}//end for
	// if valid extra bits at the end were all the same frequency - add them in
	if (n > rfLen/fchigh) {
		if (dest[idx-2]==1) {
			n = (n * fclow + rfLen/2) / rfLen;
		} else {
			n = (n * fchigh + rfLen/2) / rfLen;
		}
		memset(dest+numBits, dest[idx-1]^invert , n);
		numBits += n;
	}
	return numBits;
}
//by marshmellow  (from holiman's base)
// full fsk demod from GraphBuffer wave to decoded 1s and 0s (no mandemod)
int fskdemod(uint8_t *dest, size_t size, uint8_t rfLen, uint8_t invert, uint8_t fchigh, uint8_t fclow)
{
	// FSK demodulator
	size = fsk_wave_demod(dest, size, fchigh, fclow);
	size = aggregate_bits(dest, size, rfLen, invert, fchigh, fclow);
	return size;
}

// loop to get raw HID waveform then FSK demodulate the TAG ID from it
int HIDdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{
	if (justNoise(dest, *size)) return -1;

	size_t numStart=0, size2=*size, startIdx=0; 
	// FSK demodulator
	*size = fskdemod(dest, size2,50,1,10,8); //fsk2a
	if (*size < 96*2) return -2;
	// 00011101 bit pattern represent start of frame, 01 pattern represents a 0 and 10 represents a 1
	uint8_t preamble[] = {0,0,0,1,1,1,0,1};
	// find bitstring in array  
	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -3; //preamble not found

	numStart = startIdx + sizeof(preamble);
	// final loop, go over previously decoded FSK data and manchester decode into usable tag ID
	for (size_t idx = numStart; (idx-numStart) < *size - sizeof(preamble); idx+=2){
		if (dest[idx] == dest[idx+1]){
			return -4; //not manchester data
		}
		*hi2 = (*hi2<<1)|(*hi>>31);
		*hi = (*hi<<1)|(*lo>>31);
		//Then, shift in a 0 or one into low
		if (dest[idx] && !dest[idx+1])  // 1 0
			*lo=(*lo<<1)|1;
		else // 0 1
			*lo=(*lo<<1)|0;
	}
	return (int)startIdx;
}

// loop to get raw paradox waveform then FSK demodulate the TAG ID from it
int ParadoxdemodFSK(uint8_t *dest, size_t *size, uint32_t *hi2, uint32_t *hi, uint32_t *lo)
{
	if (justNoise(dest, *size)) return -1;
	
	size_t numStart=0, size2=*size, startIdx=0;
	// FSK demodulator
	*size = fskdemod(dest, size2,50,1,10,8); //fsk2a
	if (*size < 96) return -2;

	// 00001111 bit pattern represent start of frame, 01 pattern represents a 0 and 10 represents a 1
	uint8_t preamble[] = {0,0,0,0,1,1,1,1};

	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -3; //preamble not found

	numStart = startIdx + sizeof(preamble);
	// final loop, go over previously decoded FSK data and manchester decode into usable tag ID
	for (size_t idx = numStart; (idx-numStart) < *size - sizeof(preamble); idx+=2){
		if (dest[idx] == dest[idx+1]) 
			return -4; //not manchester data
		*hi2 = (*hi2<<1)|(*hi>>31);
		*hi = (*hi<<1)|(*lo>>31);
		//Then, shift in a 0 or one into low
		if (dest[idx] && !dest[idx+1])	// 1 0
			*lo=(*lo<<1)|1;
		else // 0 1
			*lo=(*lo<<1)|0;
	}
	return (int)startIdx;
}

uint32_t bytebits_to_byte(uint8_t *src, size_t numbits)
{
	uint32_t num = 0;
	for(int i = 0 ; i < numbits ; i++)
	{
		num = (num << 1) | (*src);
		src++;
	}
	return num;
}

//least significant bit first
uint32_t bytebits_to_byteLSBF(uint8_t *src, size_t numbits)
{
	uint32_t num = 0;
	for(int i = 0 ; i < numbits ; i++)
	{
		num = (num << 1) | *(src + (numbits-(i+1)));
	}
	return num;
}

int IOdemodFSK(uint8_t *dest, size_t size)
{
	if (justNoise(dest, size)) return -1;
	//make sure buffer has data
	if (size < 66*64) return -2;
	// FSK demodulator
	size = fskdemod(dest, size, 64, 1, 10, 8);  // FSK2a RF/64 
	if (size < 65) return -3;  //did we get a good demod?
	//Index map
	//0           10          20          30          40          50          60
	//|           |           |           |           |           |           |
	//01234567 8 90123456 7 89012345 6 78901234 5 67890123 4 56789012 3 45678901 23
	//-----------------------------------------------------------------------------
	//00000000 0 11110000 1 facility 1 version* 1 code*one 1 code*two 1 ???????? 11
	//
	//XSF(version)facility:codeone+codetwo
	//Handle the data
	size_t startIdx = 0;
	uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,1};
	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), &size, &startIdx);
	if (errChk == 0) return -4; //preamble not found

	if (!dest[startIdx+8] && dest[startIdx+17]==1 && dest[startIdx+26]==1 && dest[startIdx+35]==1 && dest[startIdx+44]==1 && dest[startIdx+53]==1){
		//confirmed proper separator bits found
		//return start position
		return (int) startIdx;
	}
	return -5;
}

// by marshmellow
// takes a array of binary values, start position, length of bits per parity (includes parity bit),
//   Parity Type (1 for odd; 0 for even; 2 for just drop it), and binary Length (length to run) 
size_t removeParity(uint8_t *BitStream, size_t startIdx, uint8_t pLen, uint8_t pType, size_t bLen)
{
	uint32_t parityWd = 0;
	size_t j = 0, bitCnt = 0;
	for (int word = 0; word < (bLen); word+=pLen){
		for (int bit=0; bit < pLen; bit++){
			parityWd = (parityWd << 1) | BitStream[startIdx+word+bit];
			BitStream[j++] = (BitStream[startIdx+word+bit]);
		}
		j--;
		// if parity fails then return 0
		if (pType != 2) {
			if (parityTest(parityWd, pLen, pType) == 0) return -1;
		}
		bitCnt+=(pLen-1);
		parityWd = 0;
	}
	// if we got here then all the parities passed
	//return ID start index and size
	return bitCnt;
}

// Ask/Biphase Demod then try to locate an ISO 11784/85 ID
// BitStream must contain previously askrawdemod and biphasedemoded data
int FDXBdemodBI(uint8_t *dest, size_t *size)
{
	//make sure buffer has enough data
	if (*size < 128) return -1;

	size_t startIdx = 0;
	uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,0,1};

	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -2; //preamble not found
	return (int)startIdx;
}

// by marshmellow
// FSK Demod then try to locate an AWID ID
int AWIDdemodFSK(uint8_t *dest, size_t *size)
{
	//make sure buffer has enough data
	if (*size < 96*50) return -1;

	if (justNoise(dest, *size)) return -2;

	// FSK demodulator
	*size = fskdemod(dest, *size, 50, 1, 10, 8);  // fsk2a RF/50 
	if (*size < 96) return -3;  //did we get a good demod?

	uint8_t preamble[] = {0,0,0,0,0,0,0,1};
	size_t startIdx = 0;
	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -4; //preamble not found
	if (*size != 96) return -5;
	return (int)startIdx;
}

// by marshmellow
// FSK Demod then try to locate an Farpointe Data (pyramid) ID
int PyramiddemodFSK(uint8_t *dest, size_t *size)
{
	//make sure buffer has data
	if (*size < 128*50) return -5;

	//test samples are not just noise
	if (justNoise(dest, *size)) return -1;

	// FSK demodulator
	*size = fskdemod(dest, *size, 50, 1, 10, 8);  // fsk2a RF/50 
	if (*size < 128) return -2;  //did we get a good demod?

	uint8_t preamble[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1};
	size_t startIdx = 0;
	uint8_t errChk = preambleSearch(dest, preamble, sizeof(preamble), size, &startIdx);
	if (errChk == 0) return -4; //preamble not found
	if (*size != 128) return -3;
	return (int)startIdx;
}

// by marshmellow
// to detect a wave that has heavily clipped (clean) samples
uint8_t DetectCleanAskWave(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
{
	uint16_t allPeaks=1;
	uint16_t cntPeaks=0;
	size_t loopEnd = 512+60;
	if (loopEnd > size) loopEnd = size;
	for (size_t i=60; i<loopEnd; i++){
		if (dest[i]>low && dest[i]<high) 
			allPeaks=0;
		else
			cntPeaks++;
	}
	if (allPeaks == 0){
		if (cntPeaks > 300) return 1;
	}
	return allPeaks;
}

// by marshmellow
// to help detect clocks on heavily clipped samples
// based on count of low to low
int DetectStrongAskClock(uint8_t dest[], size_t size, uint8_t high, uint8_t low)
{
	uint8_t fndClk[] = {8,16,32,40,50,64,128};
	size_t startwave;
	size_t i = 0;
	size_t minClk = 255;
		// get to first full low to prime loop and skip incomplete first pulse
	while ((dest[i] < high) && (i < size))
		++i;
	while ((dest[i] > low) && (i < size))
		++i;

	// loop through all samples
	while (i < size) {
		// measure from low to low
		while ((dest[i] > low) && (i < size))
			++i;
		startwave= i;
		while ((dest[i] < high) && (i < size))
			++i;
		while ((dest[i] > low) && (i < size))
			++i;
		//get minimum measured distance
		if (i-startwave < minClk && i < size)
			minClk = i - startwave;
	}
	// set clock
	for (uint8_t clkCnt = 0; clkCnt<7; clkCnt++) {
		if (minClk >= fndClk[clkCnt]-(fndClk[clkCnt]/8) && minClk <= fndClk[clkCnt]+1)
			return fndClk[clkCnt];
	}
	return 0;
}

// by marshmellow
// not perfect especially with lower clocks or VERY good antennas (heavy wave clipping)
// maybe somehow adjust peak trimming value based on samples to fix?
// return start index of best starting position for that clock and return clock (by reference)
int DetectASKClock(uint8_t dest[], size_t size, int *clock, int maxErr)
{
	size_t i=1;
	uint8_t clk[] = {255,8,16,32,40,50,64,100,128,255};
	uint8_t clkEnd = 9;
	uint8_t loopCnt = 255;  //don't need to loop through entire array...
	if (size <= loopCnt) return -1; //not enough samples

	//if we already have a valid clock
	uint8_t clockFnd=0;
	for (;i<clkEnd;++i)
		if (clk[i] == *clock) clockFnd = i;
		//clock found but continue to find best startpos

	//get high and low peak
	int peak, low;
	if (getHiLo(dest, loopCnt, &peak, &low, 75, 75) < 1) return -1;
	
	//test for large clean peaks
	if (!clockFnd){
		if (DetectCleanAskWave(dest, size, peak, low)==1){
			int ans = DetectStrongAskClock(dest, size, peak, low);
			for (i=clkEnd-1; i>0; i--){
				if (clk[i] == ans) {
					*clock = ans;
					//clockFnd = i;
					return 0;  // for strong waves i don't use the 'best start position' yet...
					//break; //clock found but continue to find best startpos [not yet]
				}
			}
		}
	}
	
	uint8_t ii;
	uint8_t clkCnt, tol = 0;
	uint16_t bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
	uint8_t bestStart[]={0,0,0,0,0,0,0,0,0};
	size_t errCnt = 0;
	size_t arrLoc, loopEnd;

	if (clockFnd>0) {
		clkCnt = clockFnd;
		clkEnd = clockFnd+1;
	}
	else clkCnt=1;

	//test each valid clock from smallest to greatest to see which lines up
	for(; clkCnt < clkEnd; clkCnt++){
		if (clk[clkCnt] <= 32){
			tol=1;
		}else{
			tol=0;
		}
		//if no errors allowed - keep start within the first clock
		if (!maxErr && size > clk[clkCnt]*2 + tol && clk[clkCnt]<128) loopCnt=clk[clkCnt]*2;
		bestErr[clkCnt]=1000;
		//try lining up the peaks by moving starting point (try first few clocks)
		for (ii=0; ii < loopCnt; ii++){
			if (dest[ii] < peak && dest[ii] > low) continue;

			errCnt=0;
			// now that we have the first one lined up test rest of wave array
			loopEnd = ((size-ii-tol) / clk[clkCnt]) - 1;
			for (i=0; i < loopEnd; ++i){
				arrLoc = ii + (i * clk[clkCnt]);
				if (dest[arrLoc] >= peak || dest[arrLoc] <= low){
				}else if (dest[arrLoc-tol] >= peak || dest[arrLoc-tol] <= low){
				}else if (dest[arrLoc+tol] >= peak || dest[arrLoc+tol] <= low){
				}else{  //error no peak detected
					errCnt++;
				}
			}
			//if we found no errors then we can stop here and a low clock (common clocks)
			//  this is correct one - return this clock
					//PrintAndLog("DEBUG: clk %d, err %d, ii %d, i %d",clk[clkCnt],errCnt,ii,i);
			if(errCnt==0 && clkCnt<7) { 
				if (!clockFnd) *clock = clk[clkCnt];
				return ii;
			}
			//if we found errors see if it is lowest so far and save it as best run
			if(errCnt<bestErr[clkCnt]){
				bestErr[clkCnt]=errCnt;
				bestStart[clkCnt]=ii;
			}
		}
	}
	uint8_t iii;
	uint8_t best=0;
	for (iii=1; iii<clkEnd; ++iii){
		if (bestErr[iii] < bestErr[best]){
			if (bestErr[iii] == 0) bestErr[iii]=1;
			// current best bit to error ratio     vs  new bit to error ratio
			if ( (size/clk[best])/bestErr[best] < (size/clk[iii])/bestErr[iii] ){
				best = iii;
			}
		}
	}
	//if (bestErr[best] > maxErr) return -1;
	if (!clockFnd) *clock = clk[best];
	return bestStart[best];
}

//by marshmellow
//detect psk clock by reading each phase shift
// a phase shift is determined by measuring the sample length of each wave
int DetectPSKClock(uint8_t dest[], size_t size, int clock)
{
	uint8_t clk[]={255,16,32,40,50,64,100,128,255}; //255 is not a valid clock
	uint16_t loopCnt = 4096;  //don't need to loop through entire array...
	if (size == 0) return 0;
	if (size<loopCnt) loopCnt = size;

	//if we already have a valid clock quit
	size_t i=1;
	for (; i < 8; ++i)
		if (clk[i] == clock) return clock;

	size_t waveStart=0, waveEnd=0, firstFullWave=0, lastClkBit=0;
	uint8_t clkCnt, fc=0, fullWaveLen=0, tol=1;
	uint16_t peakcnt=0, errCnt=0, waveLenCnt=0;
	uint16_t bestErr[]={1000,1000,1000,1000,1000,1000,1000,1000,1000};
	uint16_t peaksdet[]={0,0,0,0,0,0,0,0,0};
	fc = countFC(dest, size, 0);
	if (fc!=2 && fc!=4 && fc!=8) return -1;
	//PrintAndLog("DEBUG: FC: %d",fc);

	//find first full wave
	for (i=0; i<loopCnt; i++){
		if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
			if (waveStart == 0) {
				waveStart = i+1;
				//PrintAndLog("DEBUG: waveStart: %d",waveStart);
			} else {
				waveEnd = i+1;
				//PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
				waveLenCnt = waveEnd-waveStart;
				if (waveLenCnt > fc){
					firstFullWave = waveStart;
					fullWaveLen=waveLenCnt;
					break;
				} 
				waveStart=0;
			}
		}
	}
	//PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);
	
	//test each valid clock from greatest to smallest to see which lines up
	for(clkCnt=7; clkCnt >= 1 ; clkCnt--){
		lastClkBit = firstFullWave; //set end of wave as clock align
		waveStart = 0;
		errCnt=0;
		peakcnt=0;
		//PrintAndLog("DEBUG: clk: %d, lastClkBit: %d",clk[clkCnt],lastClkBit);

		for (i = firstFullWave+fullWaveLen-1; i < loopCnt-2; i++){
			//top edge of wave = start of new wave 
			if (dest[i] < dest[i+1] && dest[i+1] >= dest[i+2]){
				if (waveStart == 0) {
					waveStart = i+1;
					waveLenCnt=0;
				} else { //waveEnd
					waveEnd = i+1;
					waveLenCnt = waveEnd-waveStart;
					if (waveLenCnt > fc){ 
						//if this wave is a phase shift
						//PrintAndLog("DEBUG: phase shift at: %d, len: %d, nextClk: %d, ii: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+clk[clkCnt]-tol,ii+1,fc);
						if (i+1 >= lastClkBit + clk[clkCnt] - tol){ //should be a clock bit
							peakcnt++;
							lastClkBit+=clk[clkCnt];
						} else if (i<lastClkBit+8){
							//noise after a phase shift - ignore
						} else { //phase shift before supposed to based on clock
							errCnt++;
						}
					} else if (i+1 > lastClkBit + clk[clkCnt] + tol + fc){
						lastClkBit+=clk[clkCnt]; //no phase shift but clock bit
					}
					waveStart=i+1;
				}
			}
		}
		if (errCnt == 0){
			return clk[clkCnt];
		}
		if (errCnt <= bestErr[clkCnt]) bestErr[clkCnt]=errCnt;
		if (peakcnt > peaksdet[clkCnt]) peaksdet[clkCnt]=peakcnt;
	} 
	//all tested with errors 
	//return the highest clk with the most peaks found
	uint8_t best=7;
	for (i=7; i>=1; i--){
		if (peaksdet[i] > peaksdet[best]) {
			best = i;
		}
		//PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
	}
	return clk[best];
}

//by marshmellow
//detect nrz clock by reading #peaks vs no peaks(or errors)
int DetectNRZClock(uint8_t dest[], size_t size, int clock)
{
	size_t i=0;
	uint8_t clk[]={8,16,32,40,50,64,100,128,255};
	size_t loopCnt = 4096;  //don't need to loop through entire array...
	if (size == 0) return 0;
	if (size<loopCnt) loopCnt = size;

	//if we already have a valid clock quit
	for (; i < 8; ++i)
		if (clk[i] == clock) return clock;

	//get high and low peak
	int peak, low;
	if (getHiLo(dest, loopCnt, &peak, &low, 75, 75) < 1) return 0;

	//PrintAndLog("DEBUG: peak: %d, low: %d",peak,low);
	size_t ii;
	uint8_t clkCnt;
	uint8_t tol = 0;
	uint16_t peakcnt=0;
	uint16_t peaksdet[]={0,0,0,0,0,0,0,0};
	uint16_t maxPeak=0;
	//test for large clipped waves
	for (i=0; i<loopCnt; i++){
		if (dest[i] >= peak || dest[i] <= low){
			peakcnt++;
		} else {
			if (peakcnt>0 && maxPeak < peakcnt){
				maxPeak = peakcnt;
			}
			peakcnt=0;
		}
	}
	peakcnt=0;
	//test each valid clock from smallest to greatest to see which lines up
	for(clkCnt=0; clkCnt < 8; ++clkCnt){
		//ignore clocks smaller than largest peak
		if (clk[clkCnt]<maxPeak) continue;

		//try lining up the peaks by moving starting point (try first 256)
		for (ii=0; ii< loopCnt; ++ii){
			if ((dest[ii] >= peak) || (dest[ii] <= low)){
				peakcnt=0;
				// now that we have the first one lined up test rest of wave array
				for (i=0; i < ((int)((size-ii-tol)/clk[clkCnt])-1); ++i){
					if (dest[ii+(i*clk[clkCnt])]>=peak || dest[ii+(i*clk[clkCnt])]<=low){
						peakcnt++;
					}
				}
				if(peakcnt>peaksdet[clkCnt]) {
					peaksdet[clkCnt]=peakcnt;
				}
			}
		}
	}
	int iii=7;
	uint8_t best=0;
	for (iii=7; iii > 0; iii--){
		if (peaksdet[iii] > peaksdet[best]){
			best = iii;
		}
		//PrintAndLog("DEBUG: Clk: %d, peaks: %d, errs: %d, bestClk: %d",clk[iii],peaksdet[iii],bestErr[iii],clk[best]);
	}
	return clk[best];
}

// by marshmellow
// convert psk1 demod to psk2 demod
// only transition waves are 1s
void psk1TOpsk2(uint8_t *BitStream, size_t size)
{
	size_t i=1;
	uint8_t lastBit=BitStream[0];
	for (; i<size; i++){
		if (BitStream[i]==7){
			//ignore errors
		} else if (lastBit!=BitStream[i]){
			lastBit=BitStream[i];
			BitStream[i]=1;
		} else {
			BitStream[i]=0;
		}
	}
	return;
}

// by marshmellow
// convert psk2 demod to psk1 demod
// from only transition waves are 1s to phase shifts change bit
void psk2TOpsk1(uint8_t *BitStream, size_t size)
{
	uint8_t phase=0;
	for (size_t i=0; i<size; i++){
		if (BitStream[i]==1){
			phase ^=1;
		}
		BitStream[i]=phase;
	}
	return;
}

// redesigned by marshmellow adjusted from existing decode functions
// indala id decoding - only tested on 26 bit tags, but attempted to make it work for more
int indala26decode(uint8_t *bitStream, size_t *size, uint8_t *invert)
{
	//26 bit 40134 format  (don't know other formats)
	int i;
	int long_wait=29;//29 leading zeros in format
	int start;
	int first = 0;
	int first2 = 0;
	int bitCnt = 0;
	int ii;
	// Finding the start of a UID
	for (start = 0; start <= *size - 250; start++) {
		first = bitStream[start];
		for (i = start; i < start + long_wait; i++) {
			if (bitStream[i] != first) {
				break;
			}
		}
		if (i == (start + long_wait)) {
			break;
		}
	}
	if (start == *size - 250 + 1) {
		// did not find start sequence
		return -1;
	}
	// Inverting signal if needed
	if (first == 1) {
		for (i = start; i < *size; i++) {
			bitStream[i] = !bitStream[i];
		}
		*invert = 1;
	}else *invert=0;

	int iii;
	//found start once now test length by finding next one
	for (ii=start+29; ii <= *size - 250; ii++) {
		first2 = bitStream[ii];
		for (iii = ii; iii < ii + long_wait; iii++) {
			if (bitStream[iii] != first2) {
				break;
			}
		}
		if (iii == (ii + long_wait)) {
			break;
		}
	}
	if (ii== *size - 250 + 1){
		// did not find second start sequence
		return -2;
	}
	bitCnt=ii-start;

	// Dumping UID
	i = start;
	for (ii = 0; ii < bitCnt; ii++) {
		bitStream[ii] = bitStream[i++];
	}
	*size=bitCnt;
	return 1;
}

// by marshmellow - demodulate NRZ wave (both similar enough)
// peaks invert bit (high=1 low=0) each clock cycle = 1 bit determined by last peak
// there probably is a much simpler way to do this.... 
int nrzRawDemod(uint8_t *dest, size_t *size, int *clk, int *invert, int maxErr)
{
	if (justNoise(dest, *size)) return -1;
	*clk = DetectNRZClock(dest, *size, *clk);
	if (*clk==0) return -2;
	size_t i, gLen = 4096;
	if (gLen>*size) gLen = *size;
	int high, low;
	if (getHiLo(dest, gLen, &high, &low, 75, 75) < 1) return -3; //25% fuzz on high 25% fuzz on low
	int lastBit = 0;  //set first clock check
	size_t iii = 0, bitnum = 0; //bitnum counter
	uint16_t errCnt = 0, MaxBits = 1000;
	size_t bestErrCnt = maxErr+1;
	size_t bestPeakCnt = 0, bestPeakStart = 0;
	uint8_t bestFirstPeakHigh=0, firstPeakHigh=0, curBit=0, bitHigh=0, errBitHigh=0;
	uint8_t tol = 1;  //clock tolerance adjust - waves will be accepted as within the clock if they fall + or - this value + clock from last valid wave
	uint16_t peakCnt=0;
	uint8_t ignoreWindow=4;
	uint8_t ignoreCnt=ignoreWindow; //in case of noise near peak
	//loop to find first wave that works - align to clock
	for (iii=0; iii < gLen; ++iii){
		if ((dest[iii]>=high) || (dest[iii]<=low)){
			if (dest[iii]>=high) firstPeakHigh=1;
			else firstPeakHigh=0;
			lastBit=iii-*clk;
			peakCnt=0;
			errCnt=0;
			//loop through to see if this start location works
			for (i = iii; i < *size; ++i) {
				// if we are at a clock bit
				if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
					//test high/low
					if (dest[i] >= high || dest[i] <= low) {
						bitHigh = 1;
						peakCnt++;
						errBitHigh = 0;
						ignoreCnt = ignoreWindow;
						lastBit += *clk;
					} else if (i == lastBit + *clk + tol) {
						lastBit += *clk;
					}
				//else if no bars found
				} else if (dest[i] < high && dest[i] > low){
					if (ignoreCnt==0){
						bitHigh=0;
						if (errBitHigh==1) errCnt++;
						errBitHigh=0;
					} else {
						ignoreCnt--;
					}
				} else if ((dest[i]>=high || dest[i]<=low) && (bitHigh==0)) {
					//error bar found no clock...
					errBitHigh=1;
				}
				if (((i-iii) / *clk)>=MaxBits) break;
			}
			//we got more than 64 good bits and not all errors
			if (((i-iii) / *clk) > 64 && (errCnt <= (maxErr))) {
				//possible good read
				if (!errCnt || peakCnt > bestPeakCnt){
					bestFirstPeakHigh=firstPeakHigh;
					bestErrCnt = errCnt;
					bestPeakCnt = peakCnt;
					bestPeakStart = iii;
					if (!errCnt) break;  //great read - finish
				}
			}
		}
	}
	//PrintAndLog("DEBUG: bestErrCnt: %d, maxErr: %d, bestStart: %d, bestPeakCnt: %d, bestPeakStart: %d",bestErrCnt,maxErr,bestStart,bestPeakCnt,bestPeakStart);
	if (bestErrCnt > maxErr) return bestErrCnt;		

	//best run is good enough set to best run and set overwrite BinStream
	lastBit = bestPeakStart - *clk;
	memset(dest, bestFirstPeakHigh^1, bestPeakStart / *clk);
	bitnum += (bestPeakStart / *clk);
	for (i = bestPeakStart; i < *size; ++i) {
		// if expecting a clock bit
		if ((i >= lastBit + *clk - tol) && (i <= lastBit + *clk + tol)) {
			// test high/low
			if (dest[i] >= high || dest[i] <= low) {
				peakCnt++;
				bitHigh = 1;
				errBitHigh = 0;
				ignoreCnt = ignoreWindow;
				curBit = *invert;
				if (dest[i] >= high) curBit ^= 1;
				dest[bitnum++] = curBit;
				lastBit += *clk;
			//else no bars found in clock area
			} else if (i == lastBit + *clk + tol) {
				dest[bitnum++] = curBit;
				lastBit += *clk;
			}
		//else if no bars found
		} else if (dest[i] < high && dest[i] > low){
			if (ignoreCnt == 0){
				bitHigh = 0;
				if (errBitHigh == 1){
					dest[bitnum++] = 7;
					errCnt++;
				}
				errBitHigh=0;
			} else {
				ignoreCnt--;
			}
		} else if ((dest[i] >= high || dest[i] <= low) && (bitHigh == 0)) {
			//error bar found no clock...
			errBitHigh=1;
		}
		if (bitnum >= MaxBits) break;
	}
	*size = bitnum;
	return bestErrCnt;
}

//by marshmellow
//detects the bit clock for FSK given the high and low Field Clocks
uint8_t detectFSKClk(uint8_t *BitStream, size_t size, uint8_t fcHigh, uint8_t fcLow)
{
	uint8_t clk[] = {8,16,32,40,50,64,100,128,0};
	uint16_t rfLens[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
	uint8_t rfCnts[] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
	uint8_t rfLensFnd = 0;
	uint8_t lastFCcnt = 0;
	uint16_t fcCounter = 0;
	uint16_t rfCounter = 0;
	uint8_t firstBitFnd = 0;
	size_t i;
	if (size == 0) return 0;

	uint8_t fcTol = (uint8_t)(0.5+(float)(fcHigh-fcLow)/2);
	rfLensFnd=0;
	fcCounter=0;
	rfCounter=0;
	firstBitFnd=0;
	//PrintAndLog("DEBUG: fcTol: %d",fcTol);
	// prime i to first up transition
	for (i = 1; i < size-1; i++)
		if (BitStream[i] > BitStream[i-1] && BitStream[i]>=BitStream[i+1])
			break;

	for (; i < size-1; i++){
		fcCounter++;
		rfCounter++;

		if (BitStream[i] <= BitStream[i-1] || BitStream[i] < BitStream[i+1]) 
			continue;		
		// else new peak 
		// if we got less than the small fc + tolerance then set it to the small fc
		if (fcCounter < fcLow+fcTol) 
			fcCounter = fcLow;
		else //set it to the large fc
			fcCounter = fcHigh;

		//look for bit clock  (rf/xx)
		if ((fcCounter < lastFCcnt || fcCounter > lastFCcnt)){
			//not the same size as the last wave - start of new bit sequence
			if (firstBitFnd > 1){ //skip first wave change - probably not a complete bit
				for (int ii=0; ii<15; ii++){
					if (rfLens[ii] == rfCounter){
						rfCnts[ii]++;
						rfCounter = 0;
						break;
					}
				}
				if (rfCounter > 0 && rfLensFnd < 15){
					//PrintAndLog("DEBUG: rfCntr %d, fcCntr %d",rfCounter,fcCounter);
					rfCnts[rfLensFnd]++;
					rfLens[rfLensFnd++] = rfCounter;
				}
			} else {
				firstBitFnd++;
			}
			rfCounter=0;
			lastFCcnt=fcCounter;
		}
		fcCounter=0;
	}
	uint8_t rfHighest=15, rfHighest2=15, rfHighest3=15;

	for (i=0; i<15; i++){
		//PrintAndLog("DEBUG: RF %d, cnts %d",rfLens[i], rfCnts[i]);
		//get highest 2 RF values  (might need to get more values to compare or compare all?)
		if (rfCnts[i]>rfCnts[rfHighest]){
			rfHighest3=rfHighest2;
			rfHighest2=rfHighest;
			rfHighest=i;
		} else if(rfCnts[i]>rfCnts[rfHighest2]){
			rfHighest3=rfHighest2;
			rfHighest2=i;
		} else if(rfCnts[i]>rfCnts[rfHighest3]){
			rfHighest3=i;
		}
	}  
	// set allowed clock remainder tolerance to be 1 large field clock length+1 
	//   we could have mistakenly made a 9 a 10 instead of an 8 or visa versa so rfLens could be 1 FC off  
	uint8_t tol1 = fcHigh+1; 
	
	//PrintAndLog("DEBUG: hightest: 1 %d, 2 %d, 3 %d",rfLens[rfHighest],rfLens[rfHighest2],rfLens[rfHighest3]);

	// loop to find the highest clock that has a remainder less than the tolerance
	//   compare samples counted divided by
	int ii=7;
	for (; ii>=0; ii--){
		if (rfLens[rfHighest] % clk[ii] < tol1 || rfLens[rfHighest] % clk[ii] > clk[ii]-tol1){
			if (rfLens[rfHighest2] % clk[ii] < tol1 || rfLens[rfHighest2] % clk[ii] > clk[ii]-tol1){
				if (rfLens[rfHighest3] % clk[ii] < tol1 || rfLens[rfHighest3] % clk[ii] > clk[ii]-tol1){
					break;
				}
			}
		}
	}

	if (ii<0) return 0; // oops we went too far

	return clk[ii];
}

//by marshmellow
//countFC is to detect the field clock lengths.
//counts and returns the 2 most common wave lengths
//mainly used for FSK field clock detection
uint16_t countFC(uint8_t *BitStream, size_t size, uint8_t fskAdj)
{
	uint8_t fcLens[] = {0,0,0,0,0,0,0,0,0,0};
	uint16_t fcCnts[] = {0,0,0,0,0,0,0,0,0,0};
	uint8_t fcLensFnd = 0;
	uint8_t lastFCcnt=0;
	uint8_t fcCounter = 0;
	size_t i;
	if (size == 0) return 0;

	// prime i to first up transition
	for (i = 1; i < size-1; i++)
		if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1])
			break;

	for (; i < size-1; i++){
		if (BitStream[i] > BitStream[i-1] && BitStream[i] >= BitStream[i+1]){
			// new up transition
			fcCounter++;
			if (fskAdj){
				//if we had 5 and now have 9 then go back to 8 (for when we get a fc 9 instead of an 8)
				if (lastFCcnt==5 && fcCounter==9) fcCounter--;
				//if fc=9 or 4 add one (for when we get a fc 9 instead of 10 or a 4 instead of a 5)
				if ((fcCounter==9) || fcCounter==4) fcCounter++;
			// save last field clock count  (fc/xx)
			lastFCcnt = fcCounter;
			}
			// find which fcLens to save it to:
			for (int ii=0; ii<10; ii++){
				if (fcLens[ii]==fcCounter){
					fcCnts[ii]++;
					fcCounter=0;
					break;
				}
			}
			if (fcCounter>0 && fcLensFnd<10){
				//add new fc length 
				fcCnts[fcLensFnd]++;
				fcLens[fcLensFnd++]=fcCounter;
			}
			fcCounter=0;
		} else {
			// count sample
			fcCounter++;
		}
	}
	
	uint8_t best1=9, best2=9, best3=9;
	uint16_t maxCnt1=0;
	// go through fclens and find which ones are bigest 2  
	for (i=0; i<10; i++){
		// PrintAndLog("DEBUG: FC %d, Cnt %d, Errs %d",fcLens[i],fcCnts[i],errCnt);    
		// get the 3 best FC values
		if (fcCnts[i]>maxCnt1) {
			best3=best2;
			best2=best1;
			maxCnt1=fcCnts[i];
			best1=i;
		} else if(fcCnts[i]>fcCnts[best2]){
			best3=best2;
			best2=i;
		} else if(fcCnts[i]>fcCnts[best3]){
			best3=i;
		}
	}
	uint8_t fcH=0, fcL=0;
	if (fcLens[best1]>fcLens[best2]){
		fcH=fcLens[best1];
		fcL=fcLens[best2];
	} else{
		fcH=fcLens[best2];
		fcL=fcLens[best1];
	}

	// TODO: take top 3 answers and compare to known Field clocks to get top 2

	uint16_t fcs = (((uint16_t)fcH)<<8) | fcL;
	// PrintAndLog("DEBUG: Best %d  best2 %d best3 %d",fcLens[best1],fcLens[best2],fcLens[best3]);
	if (fskAdj) return fcs;	
	return fcLens[best1];
}

//by marshmellow - demodulate PSK1 wave 
//uses wave lengths (# Samples) 
int pskRawDemod(uint8_t dest[], size_t *size, int *clock, int *invert)
{
	if (size == 0) return -1;
	uint16_t loopCnt = 4096;  //don't need to loop through entire array...
	if (*size<loopCnt) loopCnt = *size;

	uint8_t curPhase = *invert;
	size_t i, waveStart=1, waveEnd=0, firstFullWave=0, lastClkBit=0;
	uint8_t fc=0, fullWaveLen=0, tol=1;
	uint16_t errCnt=0, waveLenCnt=0;
	fc = countFC(dest, *size, 0);
	if (fc!=2 && fc!=4 && fc!=8) return -1;
	//PrintAndLog("DEBUG: FC: %d",fc);
	*clock = DetectPSKClock(dest, *size, *clock);
	if (*clock == 0) return -1;
	int avgWaveVal=0, lastAvgWaveVal=0;
	//find first phase shift
	for (i=0; i<loopCnt; i++){
		if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
			waveEnd = i+1;
			//PrintAndLog("DEBUG: waveEnd: %d",waveEnd);
			waveLenCnt = waveEnd-waveStart;
			if (waveLenCnt > fc && waveStart > fc){ //not first peak and is a large wave 
				lastAvgWaveVal = avgWaveVal/(waveLenCnt);
				firstFullWave = waveStart;
				fullWaveLen=waveLenCnt;
				//if average wave value is > graph 0 then it is an up wave or a 1
				if (lastAvgWaveVal > 123) curPhase ^= 1;  //fudge graph 0 a little 123 vs 128
				break;
			} 
			waveStart = i+1;
			avgWaveVal = 0;
		}
		avgWaveVal += dest[i+2];
	}
	//PrintAndLog("DEBUG: firstFullWave: %d, waveLen: %d",firstFullWave,fullWaveLen);  
	lastClkBit = firstFullWave; //set start of wave as clock align
	//PrintAndLog("DEBUG: clk: %d, lastClkBit: %d", *clock, lastClkBit);
	waveStart = 0;
	size_t numBits=0;
	//set skipped bits
	memset(dest, curPhase^1, firstFullWave / *clock);
	numBits += (firstFullWave / *clock);
	dest[numBits++] = curPhase; //set first read bit
	for (i = firstFullWave + fullWaveLen - 1; i < *size-3; i++){
		//top edge of wave = start of new wave 
		if (dest[i]+fc < dest[i+1] && dest[i+1] >= dest[i+2]){
			if (waveStart == 0) {
				waveStart = i+1;
				waveLenCnt = 0;
				avgWaveVal = dest[i+1];
			} else { //waveEnd
				waveEnd = i+1;
				waveLenCnt = waveEnd-waveStart;
				lastAvgWaveVal = avgWaveVal/waveLenCnt;
				if (waveLenCnt > fc){  
					//PrintAndLog("DEBUG: avgWaveVal: %d, waveSum: %d",lastAvgWaveVal,avgWaveVal);
					//this wave is a phase shift
					//PrintAndLog("DEBUG: phase shift at: %d, len: %d, nextClk: %d, i: %d, fc: %d",waveStart,waveLenCnt,lastClkBit+*clock-tol,i+1,fc);
					if (i+1 >= lastClkBit + *clock - tol){ //should be a clock bit
						curPhase ^= 1;
						dest[numBits++] = curPhase;
						lastClkBit += *clock;
					} else if (i < lastClkBit+10+fc){
						//noise after a phase shift - ignore
					} else { //phase shift before supposed to based on clock
						errCnt++;
						dest[numBits++] = 7;
					}
				} else if (i+1 > lastClkBit + *clock + tol + fc){
					lastClkBit += *clock; //no phase shift but clock bit
					dest[numBits++] = curPhase;
				}
				avgWaveVal = 0;
				waveStart = i+1;
			}
		}
		avgWaveVal += dest[i+1];
	}
	*size = numBits;
	return errCnt;
}