Step by Step solution about How to resolve the algorithm Apply a digital filter (direct form II transposed) step by step in the C programming language

The C code implements a program that reads a signal data file, processes it, and prints or saves the filtered signal to the output file. Here's a detailed explanation of the code:

1. Header Files:

   • The code includes the necessary header files:
     • <stdlib.h>: for memory allocation and manipulation functions.
     • <string.h>: for string manipulation functions.
     • <stdio.h>: for input and output operations.

2. Constants and Data Structures:

   • MAX_LEN is a constant that defines the maximum length of strings used in the program.
   • vector is a user-defined data structure that represents a vector with a float* pointer to its values and an int representing its size.

3. Function extractVector:

   • This function takes a character array str as input and extracts a vector of floating-point values from the string.
   • It counts the number of space-separated tokens in the string to determine the size of the vector.
   • It allocates memory for the vector's values and stores the floating-point values obtained from the tokens in the vector.
   • It returns the extracted vector.

4. Function processSignalFile:

   • This function takes a file name fileName as input and processes a signal data file to perform filtering.
   • It opens the file and reads three lines:
     • The first line contains the coefficients for the numerator polynomial.
     • The second line contains the coefficients for the denominator polynomial.
     • The third line contains the signal data.
   • It extracts the coefficient vectors and the signal vector using the extractVector function.
   • It allocates memory for the filtered signal vector.
   • It applies the IIR (Infinite Impulse Response) filtering algorithm on the signal vector using the coefficients.
   • It returns the filtered signal vector.

5. Function printVector:

   • This function takes a vector v and an optional output file name outputFile as input.
   • If outputFile is NULL, it prints the vector values to the console.
   • Otherwise, it writes the vector values to the specified output file.

6. main Function:

   • The main function is the entry point of the program.
   • It checks the number of command-line arguments.
   • If there are not exactly two or three arguments, it prints an error message and exits.
   • If there are three arguments, it allocates memory for a string to store the message "written to " concatenated with the output file name.
   • It calls the processSignalFile function to process the signal data file and obtain the filtered signal vector.
   • It calls the printVector function to print or save the filtered signal vector.

The provided C code takes a signal data file as input and performs a filtering operation on the signal data to produce a filtered signal. Here's a detailed explanation of the code:

1. Header Files and Macros:

   • The code includes essential header files like <stdlib.h>, <string.h>, and <stdio.h> for standard C library functions and operations.
   • It defines a macro MAX_LEN with a value of 1000, which represents the maximum length of strings used in the program.

2. Structure Definition (vector):

   • A custom vector structure is defined using typedef. This structure contains two members:
     • float* values;: A pointer to an array of floating-point numbers representing the vector's values.
     • int size;: An integer representing the number of elements in the vector.

3. Function extractVector:

   • This function extracts a vector of floating-point numbers from a given character string (char* str).
   • It calculates the number of values in the string based on the spaces encountered.
   • It dynamically allocates memory for the vector's values array and initializes its size.
   • It uses the strtok function to tokenize the string, convert each token to a float, and store it in the values array.
   • Finally, it returns the extracted vector.

4. Function processSignalFile:

   • This function processes the signal data file specified by fileName and performs filtering on the signal.
   • It reads three lines from the file:
     • Line 1: Contains the first set of coefficients (coeff1) for the filter.
     • Line 2: Contains the second set of coefficients (coeff2) for the filter.
     • Line 3: Contains the signal data (signal) to be filtered.
   • It calls the extractVector function to extract these vectors from the strings.
   • It creates a new vector filteredSignal to store the filtered signal and initializes its values to zero.
   • It loops through each sample in the signal data and calculates the filtered value based on the coefficients and previous filtered values.
   • Finally, it returns the filteredSignal vector.

5. Function printVector:

   • This function is used to print the contents of a vector to either the standard output (if outputFile is NULL) or a file specified by outputFile.
   • It iterates through the vector's values and prints them in a formatted manner.

6. Main Function (main):

   • The main function is the entry point of the program.
   • It accepts two or three command-line arguments:
     • argV[1]: The name of the signal data file.
     • argV[2]: Optional output file name to save the filtered signal (if provided).
   • It checks for the correct number of arguments and prints an error message if incorrect.
   • If an output file is provided, it prints a message indicating where the results will be written.
   • It calls the processSignalFile function to process the signal data and obtain the filtered signal.
   • Finally, it calls the printVector function to print the filtered signal either to the standard output or the specified file.

7. Usage:

   • The program is designed to be run with a single input file containing signal data. An optional output file name can be provided to save the filtered signal.
   • For example, to filter a signal data file named "signal.txt" and print the filtered signal to the standard output, you would run the program as follows:

   ./program signal.txt
   

   • If you want to save the filtered signal to a file named "filtered_signal.txt," you would use:

   ./program signal.txt filtered_signal.txt
   

#include<stdlib.h>
#include<string.h>
#include<stdio.h>

#define MAX_LEN 1000

typedef struct{
	float* values;
	int size;
}vector;

vector extractVector(char* str){
	vector coeff;
	int i=0,count = 1;
	char* token;
	
	while(str[i]!=00){
		if(str[i++]==' ')
			count++;
	}
	
	coeff.values = (float*)malloc(count*sizeof(float));
	coeff.size = count;
	
	token = strtok(str," ");
	
	i = 0;
	
	while(token!=NULL){
		coeff.values[i++] = atof(token);
		token = strtok(NULL," ");
	}
	
	return coeff;
}

vector processSignalFile(char* fileName){
	int i,j;
	float sum;
	char str[MAX_LEN];
	vector coeff1,coeff2,signal,filteredSignal;
	
	FILE* fp = fopen(fileName,"r");
	
	fgets(str,MAX_LEN,fp);
	coeff1 = extractVector(str);
	
	fgets(str,MAX_LEN,fp);
	coeff2 = extractVector(str);
	
	fgets(str,MAX_LEN,fp);
	signal = extractVector(str);

        fclose(fp);
	
	filteredSignal.values = (float*)calloc(signal.size,sizeof(float));
	filteredSignal.size = signal.size;
	
	for(i=0;i<signal.size;i++){
		sum = 0;
		
		for(j=0;j<coeff2.size;j++){
			if(i-j>=0)
				sum += coeff2.values[j]*signal.values[i-j];
		}
		
		for(j=0;j<coeff1.size;j++){
			if(i-j>=0)
				sum -= coeff1.values[j]*filteredSignal.values[i-j];
		}
		
		sum /= coeff1.values[0];
		filteredSignal.values[i] = sum;
	}
	
	return filteredSignal;
}

void printVector(vector v, char* outputFile){
	int i;
	
	if(outputFile==NULL){
		printf("[");
		for(i=0;i<v.size;i++)
			printf("%.12f, ",v.values[i]);
		printf("\b\b]");
	}
	
	else{
		FILE* fp = fopen(outputFile,"w");
		for(i=0;i<v.size-1;i++)
			fprintf(fp,"%.12f, ",v.values[i]);
		fprintf(fp,"%.12f",v.values[i]);
		fclose(fp);
	}
	
}

int main(int argC,char* argV[])
{
	char *str;
	if(argC<2||argC>3)
		printf("Usage : %s <name of signal data file and optional output file.>",argV[0]);
	else{
		if(argC!=2){
			str = (char*)malloc((strlen(argV[2]) + strlen(str) + 1)*sizeof(char));
			strcpy(str,"written to ");
		}
		printf("Filtered signal %s",(argC==2)?"is:\n":strcat(str,argV[2]));
		printVector(processSignalFile(argV[1]),argV[2]);
	}
	return 0;
}