Develop Reference

What's the importance of the Offset variable in this algorithm?

What's the meaning of this variable named Offset in this algorithm ?
It's declared in the second calcCrc16 parameter.
For me it's useless bcause it's aways zero and it's used in a sum.
this algorithm generates a crc-16. I'm trying to understand this algorithm bcause a have to create a algorithm that verify crc-16, and i want to use this code as base.
public sealed class CRC
{
private readonly int _polynom;
public static readonly CRC Default = new CRC(0xA001);
public CRC(int polynom)
{
_polynom = polynom;
}
public int CalcCrc16(byte[] buffer)
{
return CalcCrc16(buffer, 0, buffer.Length, _polynom, 0);
}
public static int CalcCrc16(byte[] buffer, int offset, int bufLen, int polynom, int preset)
{
preset &= 0xFFFF;
polynom &= 0xFFFF;
var crc = preset;
for (var i = 0; i < (bufLen + 2); i++)
{
var data = buffer[(i + offset) % buffer.Length] & 0xFF;
crc ^= data;
for (var j = 0; j < 8; j++)
{
if ((crc & 0x0001) != 0)
{
crc = (crc >> 1) ^ polynom;
}
else
{
crc = crc >> 1;
}
}
}
return crc & 0xFFFF;
}
}

I created a simple example, using a small 4 byte message (in a 6 byte buffer):
using System;
namespace crc16
{
class Program
{
private static ushort Crc16(byte[] bfr, int bfrlen)
{
ushort crc = 0;
for (int i = 0; i < bfrlen; i++)
{
crc ^= bfr[i];
for (int j = 0; j < 8; j++)
// assumes twos complement math
crc = (ushort)((crc >> 1)^((0 - (crc&1)) & 0xa001));
}
return crc;
}
static void Main(string[] args)
{
ushort crc;
byte[] data = new byte[6] {0x11, 0x22, 0x33, 0x44, 0x00, 0x00};
crc = Crc16(data, 4); // generate crc
data[4] = (byte)(crc & 0xff); // append crc (lsb first)
data[5] = (byte)(crc >> 8);
crc = Crc16(data, 6); // verify crc;
Console.WriteLine("{0:X4}", crc);
return;
}
}
}

It's part of the signature of a public method, suitable whenever you want to calculate a CRC, but not on your entire buffer.
Sure, most of the time you may just use the simple version of the method, and in that case the parameter is always zero, but typically hashing and CRC implementations are built with an API like this, allowing you to calculate your CRC in chunks if you'd like.

Convert esp8266 code(part of it) to c/c++ or c#

Hi im trying to repeat this wifi baby monitor project based on esp8266:
baby monitor project
But instead of receiving data on another esp8266, I want to receive data on pc.
I'm a c # programmer and I've encountered an problem of understanding c/c++ pointers how arrays works here and receive udp.
this is esp8266 receiver source code which works without any problems, but data that it receives, passes them to DAC. And i cant figure out where i can read just values one by one which was readed by esp8266 transmiter from ADC. Also readed data from ADC is 12 bit and author of original code use all 16 bit with some compression to transfer more data, and this compression part is what i have difficulty to uderstand it
#include <Wire.h>
#include <ESP8266WiFi.h>
#include <WiFiClient.h>
#include <WiFiUdp.h>
#include "ESP8266mDNS.h"
#include <ArduinoOTA.h>
//#include "wifi_params.h"
const int mySDA = D7;
const int mySCL = D6;
const int AMPLI_MUTE_PIN = D2;
const int AMPLI_SHUTDOWN_PIN = D1;
const int RIGHT_BTN = D3;
const int LEFT_BTN = D4;
const int LED1 = D8;
const int udp_recv_port = 45990;
WiFiUDP udp;
TwoWire i2c;
#define NB_DATA_BUFS 5
uint16_t data_buf[NB_DATA_BUFS][700]; // data buffer, N buffered
unsigned int current_play_data_buf; // current data buf being played
unsigned int play_data_buf_pos; // position in the ADC data buffer
unsigned int current_recv_data_buf; // current data buf being received
bool play_waiting = true;
bool amplifier_stopped = false;
long play_waiting_at;
bool left_btn_pressed;
bool right_btn_pressed;
#define ICACHE_RAM_ATTR __attribute__((section(".iram.text")))
#define twi_sda mySDA
#define twi_scl mySCL
#define twi_dcount 0
#define twi_clockStretchLimit 10
#define SDA_LOW() (GPES = (1 << twi_sda)) //Enable SDA (becomes output and since GPO is 0 for the pin, it will pull the line low)
#define SDA_HIGH() (GPEC = (1 << twi_sda)) //Disable SDA (becomes input and since it has pullup it will go high)
#define SDA_READ() ((GPI & (1 << twi_sda)) != 0)
#define SCL_LOW() (GPES = (1 << twi_scl))
#define SCL_HIGH() (GPEC = (1 << twi_scl))
#define SCL_READ() ((GPI & (1 << twi_scl)) != 0)
static void twi_delay(unsigned char v) {
unsigned int i;
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
unsigned int reg;
for (i = 0; i<v; i++) reg = GPI;
#pragma GCC diagnostic pop
}
static inline ICACHE_RAM_ATTR bool twi_write_start(void) {
SCL_HIGH();
SDA_HIGH();
if (SDA_READ() == 0) return false;
SDA_LOW();
return true;
}
static inline ICACHE_RAM_ATTR bool twi_write_stop(void) {
uint32_t i = 0;
SCL_LOW();
SDA_LOW();
SCL_HIGH();
while (SCL_READ() == 0 && (i++) < twi_clockStretchLimit); // Clock stretching
SDA_HIGH();
return true;
}
static inline ICACHE_RAM_ATTR bool twi_write_bit(bool bit) {
uint32_t i = 0;
SCL_LOW();
if (bit) SDA_HIGH();
else SDA_LOW();
twi_delay(twi_dcount + 1);
SCL_HIGH();
while (SCL_READ() == 0 && (i++) < twi_clockStretchLimit);// Clock stretching
return true;
}
static inline ICACHE_RAM_ATTR bool twi_read_bit(void) {
uint32_t i = 0;
SCL_LOW();
SDA_HIGH();
twi_delay(twi_dcount + 2);
SCL_HIGH();
while (SCL_READ() == 0 && (i++) < twi_clockStretchLimit);// Clock stretching
bool bit = SDA_READ();
return bit;
}
static inline ICACHE_RAM_ATTR bool twi_write_byte(unsigned char byte) {
unsigned char bit;
for (bit = 0; bit < 8; bit++) {
twi_write_bit(byte & 0x80);
byte <<= 1;
}
return !twi_read_bit();//NACK/ACK
}
static inline ICACHE_RAM_ATTR unsigned char twi_read_byte(bool nack) {
unsigned char byte = 0;
unsigned char bit;
for (bit = 0; bit < 8; bit++) byte = (byte << 1) | twi_read_bit();
twi_write_bit(nack);
return byte;
}
unsigned char inline ICACHE_RAM_ATTR mytwi_writeTo(unsigned char address, unsigned char * buf, unsigned int len, unsigned char sendStop) {
unsigned int i;
if (!twi_write_start()) return 4;//line busy
if (!twi_write_byte(((address << 1) | 0) & 0xFF)) {
if (sendStop) twi_write_stop();
return 2; //received NACK on transmit of address
}
for (i = 0; i<len; i++) {
if (!twi_write_byte(buf[i])) {
if (sendStop) twi_write_stop();
return 3;//received NACK on transmit of data
}
}
if (sendStop) twi_write_stop();
i = 0;
while (SDA_READ() == 0 && (i++) < 10) {
SCL_LOW();
SCL_HIGH();
}
return 0;
}
static inline ICACHE_RAM_ATTR uint8_t DAC(uint16_t value)
{
/* value is 76543210 XXXXBA98
per the datasheet for fast write:
1 1 0 0 A2 A1 A0 0 <ACK> 0 0 PD1 PD0 D11 D10 D9 D8 <ACK> D7 D6 D5 D4 D3 D2 D1 D0 <ACK>
*/
uint8_t buf[2] = { (value >> 8) & 0x0F, (value & 0xFF) };
int ret = mytwi_writeTo(0x60, buf, 2, true);
Serial.println(value);
return ret;
}
void ICACHE_RAM_ATTR playsample_isr(void)
{
if (play_waiting) {
return;
}
DAC(data_buf[current_play_data_buf][play_data_buf_pos]);
play_data_buf_pos++;
if (play_data_buf_pos >= sizeof(data_buf[0]) / sizeof(data_buf[0][0])) {
play_data_buf_pos = 0;
current_play_data_buf++;
if (current_play_data_buf == NB_DATA_BUFS) {
current_play_data_buf = 0;
}
if (current_play_data_buf == current_recv_data_buf) {
play_waiting = true;
play_waiting_at = micros();
}
}
}
void ota_onstart(void)
{
// Disable timer when an OTA happens
timer1_detachInterrupt();
timer1_disable();
}
void ota_onprogress(unsigned int sz, unsigned int total)
{
Serial.print("OTA: "); Serial.print(sz); Serial.print("/"); Serial.print(total);
Serial.print("="); Serial.print(100 * sz / total); Serial.println("%");
}
void ota_onerror(ota_error_t err)
{
Serial.print("OTA ERROR:"); Serial.println((int)err);
}
void left_btn_intr()
{
left_btn_pressed = 1;
}
void right_btn_intr()
{
right_btn_pressed = 1;
}
void setup(void)
{
Serial.begin(115200);
Serial.println("I was built on " __DATE__ " at " __TIME__ "");
i2c.begin(mySDA, mySCL);
i2c.setClock(400000);
WiFi.mode(WIFI_STA);
WiFi.begin("valik 2", "299745buhlo");
WiFi.setSleepMode(WIFI_MODEM_SLEEP);
Serial.print("Connecting to wifi");
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.print("Cnnectd to ");
Serial.println("valik 2");
Serial.print("IP ");
Serial.println(WiFi.localIP());
ArduinoOTA.onStart(ota_onstart);
ArduinoOTA.onError(ota_onerror);
ArduinoOTA.onProgress(ota_onprogress);
ArduinoOTA.setHostname("bb-recv");
ArduinoOTA.begin();
timer1_isr_init();
timer1_attachInterrupt(playsample_isr);
timer1_enable(TIM_DIV16, TIM_EDGE, TIM_LOOP);
timer1_write(clockCyclesPerMicrosecond() / 16 * 50); //50us = 20 kHz sampling freq
udp.begin(udp_recv_port);
pinMode(AMPLI_MUTE_PIN, OUTPUT);
pinMode(AMPLI_SHUTDOWN_PIN, OUTPUT);
digitalWrite(AMPLI_SHUTDOWN_PIN, 0);
digitalWrite(AMPLI_MUTE_PIN, 0);
pinMode(LEFT_BTN, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(LEFT_BTN), left_btn_intr, FALLING);
pinMode(RIGHT_BTN, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(RIGHT_BTN), right_btn_intr, FALLING);
pinMode(LED1, OUTPUT);
digitalWrite(LED1, 0);
}
int do_undelta7(const uint8_t *val, int sz, uint16_t *out)
{
// Implement delta 7 decompression.
// First bit = 0 <=> uncompressed 15 bits following
// First bit = 1 <=> 7 bits follow representing delta
// must switch to big endian...
uint16_t last = 0;
uint8_t *ptr = (uint8_t *)&out[0];
const uint8_t *start = ptr;
for (int i = 0; i < sz; i++) {
uint16_t *ptr16 = (uint16_t *)ptr;
const int8_t firstbyte = val[i];
if (firstbyte & 0x80) {
// Delta7 compressed
// byte is CSMMMMMM
int8_t delta = firstbyte & 0x3F;
if (firstbyte & 0x40) {
delta = -delta;
}
const uint16_t value = last + delta;
*ptr16 = value;
ptr += 2;
last = value;
}
else {
// uncompressed -- switch bytes back to LE
*ptr++ = val[i + 1];
*ptr++ = val[i];
last = val[i + 1] | val[i] << 8;
i++;
}
}
return ptr - start;
}
void loop(void)
{
ArduinoOTA.handle();
int sz = udp.parsePacket();
//Serial.println(current_play_data_buf);
if (sz) {
uint8_t buf[sz];
udp.read(&buf[0], sz);
current_recv_data_buf++;
if (current_recv_data_buf == NB_DATA_BUFS) {
current_recv_data_buf = 0;
if (current_recv_data_buf == current_play_data_buf && !play_waiting) {
Serial.println("buffer overflow when receiving");
}
}
do_undelta7(buf, sz, &data_buf[current_recv_data_buf][0]);
if (play_waiting) {
Serial.print("Restarting play, was waiting (us)"); Serial.println(micros() - play_waiting_at);
// Re-enable *then* unmute in that order to avoid pops
digitalWrite(AMPLI_SHUTDOWN_PIN, 1);
digitalWrite(AMPLI_MUTE_PIN, 1);
play_waiting = false;
amplifier_stopped = false;
digitalWrite(LED1, 1);
}
Serial.println("");
}
// If not playing anything, but amplifier is still up
if (!amplifier_stopped && play_waiting) {
if ((micros() - play_waiting_at) > 2000 * 1000) {
// If nothing has been played for two seconds, shut down the amplifier
Serial.println("Shutting down amplifier!");
digitalWrite(AMPLI_SHUTDOWN_PIN, 0);
digitalWrite(AMPLI_MUTE_PIN, 0);
amplifier_stopped = true;
digitalWrite(LED1, 0);
}
}
if (left_btn_pressed) {
left_btn_pressed = 0;
digitalWrite(AMPLI_MUTE_PIN, 0);
digitalWrite(AMPLI_SHUTDOWN_PIN, 0);
}
if (right_btn_pressed) {
digitalWrite(AMPLI_SHUTDOWN_PIN, 1);
digitalWrite(AMPLI_MUTE_PIN, 1);
udp.beginPacket(udp.remoteIP(), 45990);
udp.write("sendnow");
udp.endPacket();
right_btn_pressed = 0;
}
// If the amplifier is stopped, add a delay for power saving
if (amplifier_stopped) {
delay(10);
}
}
This is my attempt to translate code to c++ for windows. But i encountered problem where programm just freeze without any errors and without closing.
#include "stdafx.h"
#include <winsock2.h>
#include <stdio.h>
#include <cstdint>
#include <ctime>
#pragma comment (lib, "ws2_32.lib")
#define NB_DATA_BUFS 5
uint16_t data_buf[NB_DATA_BUFS][700]; // data buffer, N buffered
unsigned int current_play_data_buf; // current data buf being played
unsigned int play_data_buf_pos; // position in the ADC data buffer
unsigned int current_recv_data_buf; // current data buf being received
bool play_waiting = true;
bool amplifier_stopped = false;
long play_waiting_at;
bool left_btn_pressed;
bool right_btn_pressed;
void InitWinsock()
{
WSADATA wsaData;
WSAStartup(MAKEWORD(2, 2), &wsaData);
}
int do_undelta7(const uint8_t *val, int sz, uint16_t *out)
{
// Implement delta 7 decompression.
// First bit = 0 <=> uncompressed 15 bits following
// First bit = 1 <=> 7 bits follow representing delta
// must switch to big endian...
uint16_t last = 0;
uint8_t *ptr = (uint8_t *)&out[0];
const uint8_t *start = ptr;
for (int i = 0; i < sz; i++) {
uint16_t *ptr16 = (uint16_t *)ptr;
const int8_t firstbyte = val[i];
if (firstbyte & 0x80) {
// Delta7 compressed
// byte is CSMMMMMM
int8_t delta = firstbyte & 0x3F;
if (firstbyte & 0x40) {
delta = -delta;
}
const uint16_t value = last + delta;
*ptr16 = value;
ptr += 2;
last = value;
}
else {
// uncompressed -- switch bytes back to LE
*ptr++ = val[i + 1];
*ptr++ = val[i];
last = val[i + 1] | val[i] << 8;
i++;
}
}
return ptr - start;
}
void DAC(uint16_t value)
{
/* value is 76543210 XXXXBA98
per the datasheet for fast write:
1 1 0 0 A2 A1 A0 0 <ACK> 0 0 PD1 PD0 D11 D10 D9 D8 <ACK> D7 D6 D5 D4 D3 D2 D1 D0 <ACK>
*/
uint8_t buf[2] = { (value >> 8) & 0x0F, (value & 0xFF) };
printf("%u\n", value & 0xFFF);
}
int _tmain(int argc, _TCHAR* argv[])
{
SOCKET socketC;
InitWinsock();
struct sockaddr_in serverInfo;
int len = 2000;
serverInfo.sin_family = AF_INET;
serverInfo.sin_port = htons(45990);
serverInfo.sin_addr.s_addr = inet_addr("192.168.1.105");
socketC = socket(AF_INET, SOCK_DGRAM, 0);
char buffers[16];
ZeroMemory(buffers, sizeof(buffers));
sendto(socketC, buffers, sizeof(IReleaseMarshalBuffers), 0, (sockaddr*)&serverInfo, len);
while (1)
{
sockaddr_in from;
const int paketSize = sizeof(from);
int r = paketSize;
char buffer[paketSize];
sprintf(buffer, "%.7s", "sendnow");
if (strcmp(buffer, "exit") == 0)
break;
recvfrom(socketC, buffer, sizeof(buffer), 0, (sockaddr*)&serverInfo, &len);
uint8_t buf[sizeof(buffer)];
uint8_t * bufeerPntr = (uint8_t*)buffer;
uint8_t * bufPntr = (uint8_t*)buffer;
for(int i=0;i<sizeof(buffer);i++)
{
buf[i] = buffer[i];
}
//udp.read(&buf[0], sizeof(buffer));
current_recv_data_buf++;
if (current_recv_data_buf == NB_DATA_BUFS) {
current_recv_data_buf = 0;
if (current_recv_data_buf == current_play_data_buf && !play_waiting) {
printf("buffer overflow when receiving\n");
}
}
do_undelta7(buf, sizeof(buffer), &data_buf[current_recv_data_buf][0]);
}
closesocket(socketC);
return 0;
}
This is my attempt to translate decoding part to c# (c# is much easier for me to understand) but i forced to use pointers and strange * and & things which i have difficulty to understand:
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
public class UDPListener
{
private const int listenPort = 45990;
public static int Main()
{
bool done = false;
UdpClient listener = new UdpClient(listenPort);
IPEndPoint groupEP = new IPEndPoint(IPAddress.Parse("192.168.1.3"), listenPort);
string received_data;
int BUFSIZE = 700;
byte[] receive_byte_array;
uint current_recv_data_buf = 1;
while (!done)
{
Console.WriteLine("Waiting for broadcast");
receive_byte_array = listener.Receive(ref groupEP);
Console.WriteLine("Received a broadcast from {0}", groupEP.ToString());
received_data = Encoding.ASCII.GetString(receive_byte_array, 0, receive_byte_array.Length);
unsafe
{
UInt16*[,] data_buf = new UInt16*[5, 700];
int sz = receive_byte_array.Length;
if (sz > 0)
{
byte[] buf = new byte[receive_byte_array.Length];
UInt16* f = stackalloc UInt16[2000];
//udp.read(&buf[0], sz);
buf = receive_byte_array;
current_recv_data_buf++;
UInt16 last = 0;
UInt16* #out1 = stackalloc UInt16[800];
for (int i = 0; i < 800; i++)
{
#out1[i] = (char)i;
}
//UIntPtr* ptr = (UIntPtr*)&#out[0];
UIntPtr* ptr = (UIntPtr*)&#out1[0];
UIntPtr* start = ptr;
for (int i = 0; i < sz; i++)
{
UIntPtr* ptr16 = ptr;
byte firstbyte = buf[i];
if ((firstbyte & 0x80) != 0)
{
// Delta7 compressed
// byte is CSMMMMMM
byte delta = (byte)(firstbyte & 0x3F);
if ((firstbyte & 0x40) != 0)
{
delta = (byte)(0 - delta);
}
UInt16 value = (UInt16)(last + delta);
*ptr16 = (UIntPtr)value;
ptr += 2;
last = value;
}
else
{
*ptr++ = (UIntPtr)buf[i + 1];
*ptr++ = (UIntPtr)buf[i];
last = (UInt16)(buf[i + 1] | buf[i] << 8);
i++;
}
}
for (int i = 0; i < 91; i++)
{
System.Console.WriteLine(#out1[i]);
}
string b = "";
}
}
}
listener.Close();
return 0;
}
} // end of class UDPListener

udp.read(&buf[0], sz); copies the received UDP packet into buffer buf. The function do_undelta7 then makes a decompression of the data in the input buffer to output buffer data_buf[current_recv_data_buf]. data_buf is array of buffers. The interrupt playsample_isr plays the content of the buffers in data_buf.

i missed an unsigned byte in do_undelta7
so now it's decoding well
c#
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Media;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using NAudio.Wave;
public class UDPListener
{
uint current_recv_data_buf;
static int NB_DATA_BUFS = 5;
static UInt16[] data_buf = new UInt16[700];
uint current_play_data_buf; // current data buf being played
uint play_data_buf_pos; // position in the ADC data buffer
private const int listenPort = 45990;
public static unsafe int Main()
{
bool done = false;
UdpClient listener = new UdpClient(listenPort);
IPEndPoint groupEP = new IPEndPoint(IPAddress.Parse("192.168.1.3"), listenPort);
int BUFSIZE = 700;
byte[] receive_byte_array;
uint current_recv_data_buf = 1;
List<byte> tenBuffsToPlay = new List<byte>();
int iterBuffsToPLay = 0;
byte[] byteArrToPlay = new byte[data_buf.Length * 2];
byte[] byte10ArrToPlay;
int pktcount = 0;
var sampleRate = 20000;
var frequency = 500;
var amplitude = 0.2;
var seconds = 5;
while (!done)
{
receive_byte_array = listener.Receive(ref groupEP);
if (receive_byte_array.Length > 0)
{
Console.WriteLine("received !"+pktcount++);
int sz = receive_byte_array.Length;
unsafe
{
byte[] buf = new byte[sz];
buf = receive_byte_array;
fixed (UInt16* data_bufPtr = &data_buf[0])
fixed (byte* ptrbuf = buf)
do_undelta7(ptrbuf, sz, data_bufPtr);
//string firstPart = "";
//string secondPart = "";
for (int i =0;i<data_buf.Length;i++)
{
//Console.WriteLine("Hex: {0:X}", data_buf[i]);
byteArrToPlay[i*2] = (byte)((data_buf[i] >> 8)&0x0f);
byteArrToPlay[(i*2)+1] = (byte)(data_buf[i] & 0xff);
//firstPart = Convert.ToString(byteArrToPlay[i], 2).PadLeft(4, '0');
//Console.Write(firstPart);
//secondPart = Convert.ToString(byteArrToPlay[i+1], 2).PadLeft(4, '0');
//Console.Write(secondPart+"\n");
}
//byteArrToPlay = data_buf.SelectMany(BitConverter.GetBytes).ToArray();
//foreach (var Arr in byteArrToPlay)
// {
// Console.WriteLine("Hex: {0:X}", Arr);
// }
tenBuffsToPlay.AddRange(byteArrToPlay);
iterBuffsToPLay++;
if (iterBuffsToPLay == 3)
{
byte10ArrToPlay = tenBuffsToPlay.ToArray();
/*var raw = new byte[sampleRate * seconds * 2];
var multiple = 2.0 * frequency / sampleRate;
for (int n = 0; n < sampleRate * seconds; n++)
{
var sampleSaw = ((n * multiple) % 2) - 1;
var sampleValue = sampleSaw > 0 ? amplitude : -amplitude;
var sample = (short)(sampleValue * Int16.MaxValue);
var bytes = BitConverter.GetBytes(sample);
raw[n * 2] = bytes[0];
raw[n * 2 + 1] = bytes[1];
}*/
var ms = new MemoryStream(byte10ArrToPlay);
var rs = new RawSourceWaveStream(ms, new WaveFormat(sampleRate, 16, 1));
var wo = new WaveOutEvent();
wo.Init(rs);
wo.Play();
/*while (wo.PlaybackState == PlaybackState.Playing)
{
Thread.Sleep(1);
}*/
//wo.Dispose();
/*using (MemoryStream ms = new MemoryStream())
{
WriteWavHeader(ms, false, 1, 16, 20000, (byte10ArrToPlay.Length / 2 - 45));
// Construct the sound player
ms.Write(byte10ArrToPlay, 0, byte10ArrToPlay.Length);
ms.Position = 0;
SoundPlayer player = new SoundPlayer(ms);
player.Play();
}*/
tenBuffsToPlay.Clear();
iterBuffsToPLay = 0;
}
}
}
}
listener.Close();
return 0;
}
static unsafe long do_undelta7(byte* val, int sz, UInt16* outArray)
{
// Implement delta 7 decompression.
// First bit = 0 <=> uncompressed 15 bits following
// First bit = 1 <=> 7 bits follow representing delta
// must switch to big endian...
UInt16 last = 0;
byte* ptr = (byte*)&outArray[0];
byte* start = ptr;
for (int i = 0; i < sz; i++)
{
UInt16* ptr16 = (UInt16*)ptr;
byte firstbyte = val[i];
var bit = (firstbyte & (1 << 8 - 1)) != 0;
if (bit == true)
{
// Delta7 compressed
// byte is CSMMMMMM
sbyte delta = (sbyte)(firstbyte & 0x3f);
bit = (firstbyte & (1 << 7 - 1)) != 0;
if (bit == true)
{
delta = (sbyte)(0x0 - delta);
}
UInt16 value = (UInt16)(last + delta);
*ptr16 = value;
ptr += 2;
last = value;
}
else
{
// uncompressed -- switch bytes back to LE
*ptr++ = val[i + 1];
*ptr++ = val[i];
last = (UInt16)(val[i + 1] | val[i] << 8);
i++;
}
}
return ptr - start;
}
private static void WriteWavHeader(MemoryStream stream, bool isFloatingPoint, ushort channelCount, ushort bitDepth, int sampleRate, int totalSampleCount)
{
stream.Position = 0;
stream.Write(Encoding.ASCII.GetBytes("RIFF"), 0, 4);
stream.Write(BitConverter.GetBytes((2* totalSampleCount) + 36), 0, 4);
stream.Write(Encoding.ASCII.GetBytes("WAVE"), 0, 4);
stream.Write(Encoding.ASCII.GetBytes("fmt "), 0, 4);
stream.Write(BitConverter.GetBytes(16), 0, 4);
stream.Write(BitConverter.GetBytes((ushort)(isFloatingPoint ? 3 : 1)), 0, 2);
stream.Write(BitConverter.GetBytes(channelCount), 0, 2);
stream.Write(BitConverter.GetBytes(sampleRate), 0, 4);
stream.Write(BitConverter.GetBytes(sampleRate * 2), 0, 4);
stream.Write(BitConverter.GetBytes((ushort)2), 0, 2);
stream.Write(BitConverter.GetBytes(16), 0, 2);
stream.Write(Encoding.ASCII.GetBytes("data"), 0, 4);
stream.Write(BitConverter.GetBytes(2 * totalSampleCount), 0, 4);
}
} // end of class UDPListener

Calculating CRC16 in C#

I'm trying to port an old code from C to C# which basically receives a string and returns a CRC16 of it...
The C method is as follow:
#define CRC_MASK 0x1021 /* x^16 + x^12 + x^5 + x^0 */
UINT16 CRC_Calc (unsigned char *pbData, int iLength)
{
UINT16 wData, wCRC = 0;
int i;
for ( ;iLength > 0; iLength--, pbData++) {
wData = (UINT16) (((UINT16) *pbData) << 8);
for (i = 0; i < 8; i++, wData <<= 1) {
if ((wCRC ^ wData) & 0x8000)
wCRC = (UINT16) ((wCRC << 1) ^ CRC_MASK);
else
wCRC <<= 1;
}
}
return wCRC;
}
My ported C# code is this:
private static ushort Calc(byte[] data)
{
ushort wData, wCRC = 0;
for (int i = 0; i < data.Length; i++)
{
wData = Convert.ToUInt16(data[i] << 8);
for (int j = 0; j < 8; j++, wData <<= 1)
{
var a = (wCRC ^ wData) & 0x8000;
if ( a != 0)
{
var c = (wCRC << 1) ^ 0x1021;
wCRC = Convert.ToUInt16(c);
}
else
{
wCRC <<= 1;
}
}
}
return wCRC;
}
The test string is "OPN"... It must return a uint which is (ofc) 2 bytes A8 A9 and the #CRC_MASK is the polynomial for that calculation. I did found several examples of CRC16 here and around the web, but none of them achieve this result since this CRC calculation must match the one that the device we are connecting to.
WHere is the mistake? I really appreciate any help.
Thanks! best regards
Gutemberg
UPDATE
Following the answer from #rcgldr, I put together the following sample:
_serial = new SerialPort("COM6", 19200, Parity.None, 8, StopBits.One);
_serial.Open();
_serial.Encoding = Encoding.GetEncoding(1252);
_serial.DataReceived += Serial_DataReceived;
var msg = "OPN";
var data = Encoding.GetEncoding(1252).GetBytes(msg);
var crc = BitConverter.GetBytes(Calc(data));
var msb = crc[0].ToString("X");
var lsb = crc[1].ToString("X");
//The following line must be something like: \x16OPN\x17\xA8\xA9
var cmd = string.Format(#"{0}{1}{2}\x{3}\x{4}", SYN, msg, ETB, msb, lsb);
//var cmd = "\x16OPN\x17\xA8\xA9";
_serial.Write(cmd);
The value of the cmd variable is what I'm trying to send to the device. If you have a look the the commented cmd value, this is a working string. The 2 bytes of the CRC16, goes in the last two parameters (msb and lsb). So, in the sample here, msb MUST be "\xA8" and lsb MUST be "\xA9" in order to the command to work(the CRC16 match on the device).
Any clues?
Thanks again.
UPDATE 2
For those who fall in the same case were you need to format the string with \x this is what I did to get it working:
protected string ToMessage(string data)
{
var msg = data + ETB;
var crc = CRC16.Compute(msg);
var fullMsg = string.Format(#"{0}{1}{2:X}{3:X}", SYN, msg, crc[0], crc[1]);
return fullMsg;
}
This return to me the full message that I need inclusing the \x on it. The SYN variable is '\x16' and ETB is '\x17'
Thank you all for the help!
Gutemberg

The problem here is that the message including the ETB (\x17) is 4 bytes long (the leading sync byte isn't used for the CRC): "OPN\x17" == {'O', 'P', 'N', 0x17}, which results in a CRC of {0xA8, 0xA9} to be appended to the message. So the CRC function is correct, but the original test data wasn't including the 4th byte which is 0x17.
This is a working example (at least with VS2015 express).
private static ushort Calc(byte[] data)
{
ushort wCRC = 0;
for (int i = 0; i < data.Length; i++)
{
wCRC ^= (ushort)(data[i] << 8);
for (int j = 0; j < 8; j++)
{
if ((wCRC & 0x8000) != 0)
wCRC = (ushort)((wCRC << 1) ^ 0x1021);
else
wCRC <<= 1;
}
}
return wCRC;
}

c# - left shift an entire byte array

In C#, is there a way to right/left shift an entire byte array (and subsequently adding a byte to a particular side for the last bit isn't lost)?
I know this sounds like a weird request, but I'd still like to know if its possible and/or how to begin doing it.

Just for grins. shifting and rotating bytes in a byte array. (not bitshifting)
shift left, zero fill:
mybytes.Skip(1).Concat(new byte[] { 0 }).ToArray();
shift right, zero fill:
(new byte[] {0}).Concat(mybytes.Take(mybytes.Length - 1)).ToArray();
rotate left:
mybytes.Skip(1).Concat(mybytes.Take(1)).ToArray();
rotate right:
mybytes.Skip(mbytes.Length - 1).Concat(mbytes.Take(mbytes.Length - 1)).ToArray();

Yes, you can. See the following methods I wrote:
/// <summary>
/// Rotates the bits in an array of bytes to the left.
/// </summary>
/// <param name="bytes">The byte array to rotate.</param>
public static void RotateLeft(byte[] bytes)
{
bool carryFlag = ShiftLeft(bytes);
if (carryFlag == true)
{
bytes[bytes.Length - 1] = (byte)(bytes[bytes.Length - 1] | 0x01);
}
}
/// <summary>
/// Rotates the bits in an array of bytes to the right.
/// </summary>
/// <param name="bytes">The byte array to rotate.</param>
public static void RotateRight(byte[] bytes)
{
bool carryFlag = ShiftRight(bytes);
if (carryFlag == true)
{
bytes[0] = (byte)(bytes[0] | 0x80);
}
}
/// <summary>
/// Shifts the bits in an array of bytes to the left.
/// </summary>
/// <param name="bytes">The byte array to shift.</param>
public static bool ShiftLeft(byte[] bytes)
{
bool leftMostCarryFlag = false;
// Iterate through the elements of the array from left to right.
for (int index = 0; index < bytes.Length; index++)
{
// If the leftmost bit of the current byte is 1 then we have a carry.
bool carryFlag = (bytes[index] & 0x80) > 0;
if (index > 0)
{
if (carryFlag == true)
{
// Apply the carry to the rightmost bit of the current bytes neighbor to the left.
bytes[index - 1] = (byte)(bytes[index - 1] | 0x01);
}
}
else
{
leftMostCarryFlag = carryFlag;
}
bytes[index] = (byte)(bytes[index] << 1);
}
return leftMostCarryFlag;
}
/// <summary>
/// Shifts the bits in an array of bytes to the right.
/// </summary>
/// <param name="bytes">The byte array to shift.</param>
public static bool ShiftRight(byte[] bytes)
{
bool rightMostCarryFlag = false;
int rightEnd = bytes.Length - 1;
// Iterate through the elements of the array right to left.
for (int index = rightEnd; index >= 0; index--)
{
// If the rightmost bit of the current byte is 1 then we have a carry.
bool carryFlag = (bytes[index] & 0x01) > 0;
if (index < rightEnd)
{
if (carryFlag == true)
{
// Apply the carry to the leftmost bit of the current bytes neighbor to the right.
bytes[index + 1] = (byte)(bytes[index + 1] | 0x80);
}
}
else
{
rightMostCarryFlag = carryFlag;
}
bytes[index] = (byte)(bytes[index] >> 1);
}
return rightMostCarryFlag;
}

It seems you are performing bit operations on large amount of bits storing them in a byte array. Consider using BitArray class and BitVector32 Structure. Depending on what you are doing with bits you can create a class like this. Note that shifting works in O(1) instead of O(n).
public class BitRing : IEnumerable<bool>
{
private readonly BitArray m_InnerBitArray;
private int m_StarIndex;
public BitRing(byte[] bytes)
{
m_InnerBitArray = new BitArray(bytes);
m_StarIndex = 0;
}
public void ShiftLeft()
{
m_StarIndex++;
}
public void ShiftRight()
{
m_StarIndex--;
}
public bool this[int i]
{
get
{
int index = GetIndex(i);
return m_InnerBitArray[index];
}
set
{
int index = GetIndex(i);
m_InnerBitArray[index] = value;
}
}
private int GetIndex(int i)
{
return i - m_StarIndex%m_InnerBitArray.Count;
}
public IEnumerator<bool> GetEnumerator()
{
for (int i = m_StarIndex; i < m_InnerBitArray.Count; i++)
{
yield return m_InnerBitArray[i];
}
for (int i = 0; i < m_StarIndex; i++)
{
yield return m_InnerBitArray[i];
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}

I've given it some more thought and realized that this probably fits the question better:
public static void Main()
{
byte[] bytes = new byte[] { 0xFF, 0x01, 0x80, 0x81 };
Stack<bool> bitStack = CreateBitStack(bytes);
ShiftLeftExpand(bitStack, 1);
byte[] newBytes = CreateByteArray(bitStack);
}
public static void ShiftLeftExpand(Stack<bool> bitStack, int count)
{
while (count-- > 0)
{
bitStack.Push(false);
}
}
public static Stack<bool> CreateBitStack(byte[] bytes)
{
Stack<bool> bitStack = new Stack<bool>(bytes.Length * 8);
for (int bytePosition = 0; bytePosition < bytes.Length; bytePosition++)
{
for (int bitPosition = 7; bitPosition >= 0; bitPosition--)
{
int bitMask = 0x01 << bitPosition;
bitStack.Push((bytes[bytePosition] & bitMask) > 0);
}
}
return bitStack;
}
public static byte[] CreateByteArray(Stack<bool> bitStack)
{
int newArrayLength = (int)Math.Ceiling(bitStack.Count / 8.0);
byte[] bytes = new byte[newArrayLength];
int bitCounter = 0;
while (bitStack.Count > 0)
{
bool? bitValue = bitStack.Pop();
int bitPosition = bitCounter % 8;
int bytePosition = newArrayLength - 1 - bitCounter / 8;
if (bitValue == true)
{
bytes[bytePosition] = (byte)(bytes[bytePosition] | (0x01 << bitPosition));
}
bitCounter++;
}
return bytes;
}
A similar technique can be applied to perform the right shift.

Linq way:
static class Shifter
{
public static byte[] ShiftLeft(this byte[] array, int n)
{
var a = array.Select(x => (byte)(x >> 8 - n % 8)).Concat(new byte[(7 + n) / 8]).Select((x, i) => new Tuple<int, byte>(i - (n % 8 == 0 ? 0 : 1), x));
var b = array.Select(x => (byte)(x << n % 8)).Concat(new byte[n / 8]).Select((x, i) => new Tuple<int, byte>(i, x));
return (from x in a
join y in b on x.Item1 equals y.Item1 into yy
from y in yy.DefaultIfEmpty()
select (byte)(x.Item2 | (y == null ? 0 : y.Item2))).ToArray();
}
public static byte[] ShiftRight(this byte[] array, int n)
{
return (new byte[n/8]).Concat(ShiftLeft(array, (8 - (n%8))%8)).ToArray();
}
}

I don't think there's a built-in way. I implemented the shift-left operation you described below (assuming little endian). It's not quite as elegant as you can do with x86 assembly (shift with carry instructions), but pretty close to what you could do with C.
Alternately, you can almost use the BigInteger struct (.NET 4 and above) which has a constructor that takes a byte array and a ToByteArray method. But its shift left operation sign-extends the high byte and its shift right operation truncates. So you'd need to compensate for both to get the exact behavior you described.
// Left-shifts a byte array in place. Assumes little-endian. Throws on overflow.
static public void ShiftByteArrayLeft(byte[] array)
{
if (array == null)
throw new ArgumentNullException("array");
if (array[array.Length - 1] >= 0x80)
throw new OverflowException();
// move left-to-right, left-shifting each byte
for (int i = array.Length - 1; i >= 1; --i)
{
// left-shift current byte
array[i] <<= 1;
// carry the bit from the next/right byte if needed
if (array[i - 1] >= 0x80)
++array[i];
}
// finally shift the left-shift the right-most byte
array[0] <<= 1;
}
// Left-shifts a byte array in place. Assumes little-endian. Grows array as needed.
static public void ShiftByteArrayLeftAutoGrow(ref byte[] array)
{
if (array == null)
throw new ArgumentNullException("array");
if (array[array.Length - 1] >= 0x80)
{
// allocate a bigger array and do the left-shift on it
byte[] oldArray = array;
array = new byte[oldArray.Length + 1];
Array.Copy(oldArray, 0, array, 0, oldArray.Length);
}
ShiftByteArrayLeft(array);
}

Shift left:
for (int i = byteArray.Length - 1; i >= 0; i--) byteArray[i] = (byte)((byteArray[i] << 1) | ((i == 0) ? 0 : byteArray[i - 1] >> 7));
Shift right:
for (int i = 0; i <= byteArray.Length - 1; i++) byteArray[i] = (byte)((byteArray[i] >> 1) | ((i == byteArray.Length - 1) ? 0 : byteArray[i + 1] << 7));

These two functions will shift the bits in an array of bytes the specified amount, shifting them into neighboring bytes as needed. Optionally, they can wrap the bits from one end of the array to the other. Note that they create a new array, but the code can be easily changed to modify the passed 'array' instead...
public static byte[] ShiftRight(byte[] array, int shift, bool wrap = false) {
if(shift < 0) {
throw new ArgumentOutOfRangeException("shift");
} else if(shift == 0) {
return (byte[])array.Clone();
} else {
if(wrap) shift %= (array.Length * 8);
if(shift >= (array.Length * 8)) return new byte[array.Length];
var offset = (shift / 8);
shift %= 8;
var ʀ = new byte[array.Length];
for(var ɪ = 0; ɪ < ʀ.Length; ɪ++) {
var indexL_ɪ = (ɪ + offset);
var indexH_ɪ = (ɪ + offset + 1);
if(wrap) {
if(indexL_ɪ >= array.Length) indexL_ɪ -= array.Length;
if(indexH_ɪ >= array.Length) indexH_ɪ -= array.Length;
}
if(indexL_ɪ < array.Length) ʀ[ɪ] = (byte)(array[indexL_ɪ] >> shift);
if(indexH_ɪ < array.Length) ʀ[ɪ] |= (byte)(array[indexH_ɪ] << (8 - shift));
}
return ʀ;
}
}
public static byte[] ShiftLeft(byte[] array, int shift, bool wrap = false) {
if(shift < 0) {
throw new ArgumentOutOfRangeException("shift");
} else if(shift == 0) {
return (byte[])array.Clone();
} else {
if(wrap) shift %= (array.Length * 8);
if(shift >= (array.Length * 8)) return new byte[array.Length];
var offset = (shift / 8);
shift %= 8;
for(var ɪ = 0; ɪ < ʀ.Length; ɪ++) {
var indexL_ɪ = (ɪ - offset - 1);
var indexH_ɪ = (ɪ - offset);
if(wrap) {
if(indexL_ɪ < 0) indexL_ɪ += array.Length;
if(indexH_ɪ < 0) indexH_ɪ += array.Length;
}
if(indexL_ɪ >= 0) ʀ[ɪ] = (byte)(array[indexL_ɪ] >> (8 - shift));
if(indexH_ɪ >= 0) ʀ[ɪ] |= (byte)(array[indexH_ɪ] << shift);
}
return ʀ;
}
}

Encode integer as variable-length big-endian byte-array

I need to write an integer to a byte array such that leading zeros are omitted and the bytes are written in big endian order.
Example:
int original = 0x00123456;
byte[] encoded = Encode(original); // == new byte[] { 0x12, 0x34, 0x56 };
int decoded = Decode(encoded); // == 0x123456
My Decode method:
private static int Decode(byte[] buffer, int index, int length)
{
int result = 0;
while (length > 0)
{
result = (result << 8) | buffer[index];
index++;
length--;
}
return result;
}
I'm struggling to come up with an Encode method that doesn't require a temporary buffer or reverses the bytes after writing them in little endian order. Can anyone help?
private static int Encode(int value, byte[] buffer, int index)
{
}

As per OP's request, here is a version without loops for a 32-bit number:
private static int Encode(int value, byte[] buffer, int index)
{
byte temp;
bool leading = true;
temp = (value >> 24) & 0xFF;
if (temp > 0) {
buffer[index++] = temp;
leading = false;
}
temp = (value >> 16) & 0xFF;
if (temp > 0 || leading == false) {
buffer[index++] = temp;
leading = false;
}
temp = (value >> 8) & 0xFF;
if (temp > 0 || leading == false) {
buffer[index++] = temp;
leading = false;
}
temp = value & 0xFF;
buffer[index++] = temp;
return index;
}
Version using a loop for 32-bit numbers:
private static int Encode(int value, byte[] buffer, int index)
{
int length = 0;
for (int i = 3; i >= 0; i++) {
byte temp = (byte)(value >> (8 * i));
if (temp > 0 || length > 0) {
buffer[index++] = temp;
length++;
}
}
return length;
}
Note that this version doesn't write anything if the input is just 0.

private static int Encode(int value, byte[] buffer, int index)
{
int length = 0;
int valueCopy = value;
while (valueCopy != 0)
{
valueCopy >>= 8;
length++;
}
for (int i = 0; i < length; i++)
{
buffer[index + length - i - 1] = (byte)value;
value >>= 8;
}
return length;
}

Note that you are saving the value to a variable Length byte array. If you save these byteArray, you need save also the length.
You can see the protected Functions Write7BitEncodedInt from BinaryWriter and Read7BitEncodedInt from BinaryReader.
These functions save storage on disk for positive numbers. A number 0-128 needs only one byte.
Microsoft uses these functions to store/retrieve the String length prefix when save to Stream.
To use these Functions, you can create own Class derived from BinaryReader / BinaryWriter.