/* package whatever; // don't place package name! */ /* This source code accompanies the article, "Using The Golay Error Detection And Correction Code", by Hank Wallace. This program demonstrates use of the Golay code. Usage: G DATA Encode/Correct/Verify/Test where DATA is the data to be encoded, codeword to be corrected, or codeword to be checked for errors. DATA is hexadecimal. Examples: G 555 E encodes information value 555 and prints a codeword G ABC123 C corrects codeword ABC123 G ABC123 V checks codeword ABC123 for errors G ABC123 T tests routines, ABC123 is a dummy parameter This program may be freely incorporated into your programs as needed. It compiles under Borland's Turbo C 2.0. No warranty of any kind is granted. */ #include "stdio.h" #include "conio.h" #define POLY 0xAE3 /* or use the other polynomial, 0xC75 */ /* ====================================================== */ unsigned long golay(unsigned long cw) /* This function calculates [23,12] Golay codewords. The format of the returned longint is [checkbits(11),data(12)]. */ { int i; unsigned long c; cw&=0xfffl; c=cw; /* save original codeword */ for (i=1; i<=12; i++) /* examine each data bit */ { if (cw & 1) /* test data bit */ cw^=POLY; /* XOR polynomial */ cw>>=1; /* shift intermediate result */ } return((cw<<12)|c); /* assemble codeword */ } /* ====================================================== */ int parity(unsigned long cw) /* This function checks the overall parity of codeword cw. If parity is even, 0 is returned, else 1. */ { unsigned char p; /* XOR the bytes of the codeword */ p=*(unsigned char*)&cw; p^=*((unsigned char*)&cw+1); p^=*((unsigned char*)&cw+2); /* XOR the halves of the intermediate result */ p=p ^ (p>>4); p=p ^ (p>>2); p=p ^ (p>>1); /* return the parity result */ return(p & 1); } /* ====================================================== */ unsigned long syndrome(unsigned long cw) /* This function calculates and returns the syndrome of a [23,12] Golay codeword. */ { int i; cw&=0x7fffffl; for (i=1; i<=12; i++) /* examine each data bit */ { if (cw & 1) /* test data bit */ cw^=POLY; /* XOR polynomial */ cw>>=1; /* shift intermediate result */ } return(cw<<12); /* value pairs with upper bits of cw */ } /* ====================================================== */ int weight(unsigned long cw) /* This function calculates the weight of 23 bit codeword cw. */ { int bits,k; /* nibble weight table */ const char wgt[16] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4}; bits=0; /* bit counter */ k=0; /* do all bits, six nibbles max */ while ((k<6) && (cw)) { bits=bits+wgt[cw & 0xf]; cw>>=4; k++; } return(bits); } /* ====================================================== */ unsigned long rotate_left(unsigned long cw, int n) /* This function rotates 23 bit codeword cw left by n bits. */ { int i; if (n != 0) { for (i=1; i<=n; i++) { if ((cw & 0x400000l) != 0) cw=(cw << 1) | 1; else cw<<=1; } } return(cw & 0x7fffffl); } /* ====================================================== */ unsigned long rotate_right(unsigned long cw, int n) /* This function rotates 23 bit codeword cw right by n bits. */ { int i; if (n != 0) { for (i=1; i<=n; i++) { if ((cw & 1) != 0) cw=(cw >> 1) | 0x400000l; else cw>>=1; } } return(cw & 0x7fffffl); } /* ====================================================== */ unsigned long correct(unsigned long cw, int *errs) /* This function corrects Golay [23,12] codeword cw, returning the corrected codeword. This function will produce the corrected codeword for three or fewer errors. It will produce some other valid Golay codeword for four or more errors, possibly not the intended one. *errs is set to the number of bit errors corrected. */ { unsigned char w; /* current syndrome limit weight, 2 or 3 */ unsigned long mask; /* mask for bit flipping */ int i,j; /* index */ unsigned long s, /* calculated syndrome */ cwsaver; /* saves initial value of cw */ cwsaver=cw; /* save */ *errs=0; w=3; /* initial syndrome weight threshold */ j=-1; /* -1 = no trial bit flipping on first pass */ mask=1; while (j<23) /* flip each trial bit */ { if (j != -1) /* toggle a trial bit */ { if (j>0) /* restore last trial bit */ { cw=cwsaver ^ mask; mask+=mask; /* point to next bit */ } cw=cwsaver ^ mask; /* flip next trial bit */ w=2; /* lower the threshold while bit diddling */ } s=syndrome(cw); /* look for errors */ if (s) /* errors exist */ { for (i=0; i<23; i++) /* check syndrome of each cyclic shift */ { if ((*errs=weight(s)) <= w) /* syndrome matches error pattern */ { cw=cw ^ s; /* remove errors */ cw=rotate_right(cw,i); /* unrotate data */ return(s=cw); } else { cw=rotate_left(cw,1); /* rotate to next pattern */ s=syndrome(cw); /* calc new syndrome */ } } j++; /* toggle next trial bit */ } else return(cw); /* return corrected codeword */ } return(cwsaver); /* return original if no corrections */ } /* correct */ /* ====================================================== */ int decode(int correct_mode, int *errs, unsigned long *cw) /* This function decodes codeword *cw in one of two modes. If correct_mode is nonzero, error correction is attempted, with *errs set to the number of bits corrected, and returning 0 if no errors exist, or 1 if parity errors exist. If correct_mode is zero, error detection is performed on *cw, returning 0 if no errors exist, 1 if an overall parity error exists, and 2 if a codeword error exists. */ { unsigned long parity_bit; if (correct_mode) /* correct errors */ { parity_bit=*cw & 0x800000l; /* save parity bit */ *cw&=~0x800000l; /* remove parity bit for correction */ *cw=correct(*cw, errs); /* correct up to three bits */ *cw|=parity_bit; /* restore parity bit */ /* check for 4 bit errors */ if (parity(*cw)) /* odd parity is an error */ return(1); return(0); /* no errors */ } else /* detect errors only */ { *errs=0; if (parity(*cw)) /* odd parity is an error */ { *errs=1; return(1); } if (syndrome(*cw)) { *errs=1; return(2); } else return(0); /* no errors */ } } /* decode */ /* ====================================================== */ void golay_test(void) /* This function tests the Golay routines for detection and correction of various patterns of error_limit bit errors. The error_mask cycles over all possible values, and error_limit selects the maximum number of induced errors. */ { unsigned long error_mask, /* bitwise mask for inducing errors */ trashed_codeword, /* the codeword for trial correction */ virgin_codeword; /* the original codeword without errors */ unsigned char pass=1, /* assume test passes */ error_limit=3; /* select number of induced bit errors here */ int error_count; /* receives number of errors corrected */ virgin_codeword=golay(0x555); /* make a test codeword */ if (parity(virgin_codeword)) virgin_codeword^=0x800000l; for (error_mask=0; error_mask<0x800000l; error_mask++) { /* filter the mask for the selected number of bit errors */ if (weight(error_mask) <= error_limit) /* you can make this faster! */ { trashed_codeword=virgin_codeword ^ error_mask; /* induce bit errors */ decode(1,&error_count,&trashed_codeword); /* try to correct bit errors */ if (trashed_codeword ^ virgin_codeword) { weight(error_mask),error_mask); pass=0; } if (kbhit()) /* look for user input */ { if (getch() == 27) return; /* escape exits */ /* other key prints status */ } } } } /* ====================================================== */ void main(int argument_count, char *argument[]) { int i,j; unsigned long l,g; const char *errmsg = "Usage: G DATA Encode/Correct/Verify/Test\n\n" " where DATA is the data to be encoded, codeword to be corrected,\n" " or codeword to be checked for errors. DATA is hexadecimal.\n\n" "Examples:\n\n" " G 555 E encodes information value 555 and prints a codeword\n" " G ABC123 C corrects codeword ABC123\n" " G ABC123 V checks codeword ABC123 for errors\n" " G ABC123 T tests routines, ABC123 is a dummy parameter\n\n"; if (argument_count != 3) { } { } switch (toupper(*argument[2])) { case 'E': /* encode */ l&=0xfff; l=golay(l); if (parity(l)) l^=0x800000l; break; case 'V': /* verify */ if (decode(0,&i,&l)) else break; case 'C': /* correct */ g=l; /* save initial codeword */ j=decode(1,&i,&l); if ((j) && (i)) "resulting in codeword %lX with a parity error.\n",g,i,l); else if ((j == 0) && (i)) else if ((j) && (i == 0)) else if ((j == 0) && (i == 0)) break; case 'T': /* test */ golay_test(); break; default: } } /* end of G.C */ import java.util.*; import java.lang.*; import java.io.*; /* Name of the class has to be "Main" only if the class is public. */ class Ideone { public static void main (String[] args) throws java.lang.Exception { // your code goes here } }
import java.util.Scanner; import java.util.Timer; import java.util.TimerTask; public class QuizApp { static int currentQuestionIndex = 0; static int userScore = 0; static Question[] questions; static Timer timer; public static void main(String[] args) { initializeQuestions(); startQuiz(); } static void initializeQuestions() { questions = new Question[3]; questions[0] = new Question("Where was the first example of paper money used?", new String[] { "Greece", "Turkey", "China", "Russia" }, 2); questions[1] = new Question("Who is generally considered the inventor of the motor car?", new String[] { "Henry Ford", "Karl Benz", "Henry M. Leland", "Gottlieb Daimler" }, 1); questions[2] = new Question("What color is an airplane's famous black box?", new String[] { "Orange", "Red", "Black", "White" }, 0); } static void startQuiz() { Scanner scanner = new Scanner(System.in); System.out.println("Welcome to the Quiz!"); System.out.println("--------------------"); timer = new Timer(); timer.schedule(new TimerTask() { public void run() { System.out.println("\nTime's up! Moving to the next question."); displayNextQuestion(); } }, 20000); displayNextQuestion(); } static void displayNextQuestion() { if (currentQuestionIndex < questions.length) { Question currentQuestion = questions[currentQuestionIndex]; System.out.println("\n" + currentQuestion.getQuestionText()); for (int i = 0; i < currentQuestion.getOptions().length; i++) { System.out.println((i + 1) + ". " + currentQuestion.getOptions()[i]); } Scanner scanner = new Scanner(System.in); System.out.print("Select your answer (1-" + currentQuestion.getOptions().length + "): "); int userAnswer = scanner.nextInt() - 1; if (userAnswer == currentQuestion.getCorrectAnswer()) { userScore++; } currentQuestionIndex++; timer.cancel(); timer = new Timer(); timer.schedule(new TimerTask() { public void run() { System.out.println("\nTime's up! Moving to the next question."); displayNextQuestion(); } }, 20000); displayNextQuestion(); } else { endQuiz(); } } static void endQuiz() { System.out.println("\nQuiz Finished!"); System.out.println("Your score: " + userScore + "/" + questions.length); System.out.println("Thank you for playing!"); } } class Question { private String questionText; private String[] options; private int correctAnswer; public Question(String questionText, String[] options, int correctAnswer) { this.questionText = questionText; this.options = options; this.correctAnswer = correctAnswer; } public String getQuestionText() { return questionText; } public String[] getOptions() { return options; } public int getCorrectAnswer() { return correctAnswer; } }
/* package whatever; // don't place package name! */ /* This source code accompanies the article, "Using The Golay Error Detection And Correction Code", by Hank Wallace. This program demonstrates use of the Golay code. Usage: G DATA Encode/Correct/Verify/Test where DATA is the data to be encoded, codeword to be corrected, or codeword to be checked for errors. DATA is hexadecimal. Examples: G 555 E encodes information value 555 and prints a codeword G ABC123 C corrects codeword ABC123 G ABC123 V checks codeword ABC123 for errors G ABC123 T tests routines, ABC123 is a dummy parameter This program may be freely incorporated into your programs as needed. It compiles under Borland's Turbo C 2.0. No warranty of any kind is granted. */ #include "stdio.h" #include "conio.h" #define POLY 0xAE3 /* or use the other polynomial, 0xC75 */ /* ====================================================== */ unsigned long golay(unsigned long cw) /* This function calculates [23,12] Golay codewords. The format of the returned longint is [checkbits(11),data(12)]. */ { int i; unsigned long c; cw&=0xfffl; c=cw; /* save original codeword */ for (i=1; i<=12; i++) /* examine each data bit */ { if (cw & 1) /* test data bit */ cw^=POLY; /* XOR polynomial */ cw>>=1; /* shift intermediate result */ } return((cw<<12)|c); /* assemble codeword */ } /* ====================================================== */ int parity(unsigned long cw) /* This function checks the overall parity of codeword cw. If parity is even, 0 is returned, else 1. */ { unsigned char p; /* XOR the bytes of the codeword */ p=*(unsigned char*)&cw; p^=*((unsigned char*)&cw+1); p^=*((unsigned char*)&cw+2); /* XOR the halves of the intermediate result */ p=p ^ (p>>4); p=p ^ (p>>2); p=p ^ (p>>1); /* return the parity result */ return(p & 1); } /* ====================================================== */ unsigned long syndrome(unsigned long cw) /* This function calculates and returns the syndrome of a [23,12] Golay codeword. */ { int i; cw&=0x7fffffl; for (i=1; i<=12; i++) /* examine each data bit */ { if (cw & 1) /* test data bit */ cw^=POLY; /* XOR polynomial */ cw>>=1; /* shift intermediate result */ } return(cw<<12); /* value pairs with upper bits of cw */ } /* ====================================================== */ int weight(unsigned long cw) /* This function calculates the weight of 23 bit codeword cw. */ { int bits,k; /* nibble weight table */ const char wgt[16] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4}; bits=0; /* bit counter */ k=0; /* do all bits, six nibbles max */ while ((k<6) && (cw)) { bits=bits+wgt[cw & 0xf]; cw>>=4; k++; } return(bits); } /* ====================================================== */ unsigned long rotate_left(unsigned long cw, int n) /* This function rotates 23 bit codeword cw left by n bits. */ { int i; if (n != 0) { for (i=1; i<=n; i++) { if ((cw & 0x400000l) != 0) cw=(cw << 1) | 1; else cw<<=1; } } return(cw & 0x7fffffl); } /* ====================================================== */ unsigned long rotate_right(unsigned long cw, int n) /* This function rotates 23 bit codeword cw right by n bits. */ { int i; if (n != 0) { for (i=1; i<=n; i++) { if ((cw & 1) != 0) cw=(cw >> 1) | 0x400000l; else cw>>=1; } } return(cw & 0x7fffffl); } /* ====================================================== */ unsigned long correct(unsigned long cw, int *errs) /* This function corrects Golay [23,12] codeword cw, returning the corrected codeword. This function will produce the corrected codeword for three or fewer errors. It will produce some other valid Golay codeword for four or more errors, possibly not the intended one. *errs is set to the number of bit errors corrected. */ { unsigned char w; /* current syndrome limit weight, 2 or 3 */ unsigned long mask; /* mask for bit flipping */ int i,j; /* index */ unsigned long s, /* calculated syndrome */ cwsaver; /* saves initial value of cw */ cwsaver=cw; /* save */ *errs=0; w=3; /* initial syndrome weight threshold */ j=-1; /* -1 = no trial bit flipping on first pass */ mask=1; while (j<23) /* flip each trial bit */ { if (j != -1) /* toggle a trial bit */ { if (j>0) /* restore last trial bit */ { cw=cwsaver ^ mask; mask+=mask; /* point to next bit */ } cw=cwsaver ^ mask; /* flip next trial bit */ w=2; /* lower the threshold while bit diddling */ } s=syndrome(cw); /* look for errors */ if (s) /* errors exist */ { for (i=0; i<23; i++) /* check syndrome of each cyclic shift */ { if ((*errs=weight(s)) <= w) /* syndrome matches error pattern */ { cw=cw ^ s; /* remove errors */ cw=rotate_right(cw,i); /* unrotate data */ return(s=cw); } else { cw=rotate_left(cw,1); /* rotate to next pattern */ s=syndrome(cw); /* calc new syndrome */ } } j++; /* toggle next trial bit */ } else return(cw); /* return corrected codeword */ } return(cwsaver); /* return original if no corrections */ } /* correct */ /* ====================================================== */ int decode(int correct_mode, int *errs, unsigned long *cw) /* This function decodes codeword *cw in one of two modes. If correct_mode is nonzero, error correction is attempted, with *errs set to the number of bits corrected, and returning 0 if no errors exist, or 1 if parity errors exist. If correct_mode is zero, error detection is performed on *cw, returning 0 if no errors exist, 1 if an overall parity error exists, and 2 if a codeword error exists. */ { unsigned long parity_bit; if (correct_mode) /* correct errors */ { parity_bit=*cw & 0x800000l; /* save parity bit */ *cw&=~0x800000l; /* remove parity bit for correction */ *cw=correct(*cw, errs); /* correct up to three bits */ *cw|=parity_bit; /* restore parity bit */ /* check for 4 bit errors */ if (parity(*cw)) /* odd parity is an error */ return(1); return(0); /* no errors */ } else /* detect errors only */ { *errs=0; if (parity(*cw)) /* odd parity is an error */ { *errs=1; return(1); } if (syndrome(*cw)) { *errs=1; return(2); } else return(0); /* no errors */ } } /* decode */ /* ====================================================== */ void golay_test(void) /* This function tests the Golay routines for detection and correction of various patterns of error_limit bit errors. The error_mask cycles over all possible values, and error_limit selects the maximum number of induced errors. */ { unsigned long error_mask, /* bitwise mask for inducing errors */ trashed_codeword, /* the codeword for trial correction */ virgin_codeword; /* the original codeword without errors */ unsigned char pass=1, /* assume test passes */ error_limit=3; /* select number of induced bit errors here */ int error_count; /* receives number of errors corrected */ virgin_codeword=golay(0x555); /* make a test codeword */ if (parity(virgin_codeword)) virgin_codeword^=0x800000l; for (error_mask=0; error_mask<0x800000l; error_mask++) { /* filter the mask for the selected number of bit errors */ if (weight(error_mask) <= error_limit) /* you can make this faster! */ { trashed_codeword=virgin_codeword ^ error_mask; /* induce bit errors */ decode(1,&error_count,&trashed_codeword); /* try to correct bit errors */ if (trashed_codeword ^ virgin_codeword) { printf("Unable to correct %d errors induced with error mask = 0x%lX\n", weight(error_mask),error_mask); pass=0; } if (kbhit()) /* look for user input */ { if (getch() == 27) return; /* escape exits */ /* other key prints status */ printf("Current test count = %ld of %ld\n",error_mask,0x800000l); } } } printf("Golay test %s!\n",pass?"PASSED":"FAILED"); } /* ====================================================== */ void main(int argument_count, char *argument[]) { int i,j; unsigned long l,g; const char *errmsg = "Usage: G DATA Encode/Correct/Verify/Test\n\n" " where DATA is the data to be encoded, codeword to be corrected,\n" " or codeword to be checked for errors. DATA is hexadecimal.\n\n" "Examples:\n\n" " G 555 E encodes information value 555 and prints a codeword\n" " G ABC123 C corrects codeword ABC123\n" " G ABC123 V checks codeword ABC123 for errors\n" " G ABC123 T tests routines, ABC123 is a dummy parameter\n\n"; if (argument_count != 3) { printf(errmsg); exit(0); } if (sscanf(argument[1],"%lx",&l) != 1) { printf(errmsg); exit(0); } switch (toupper(*argument[2])) { case 'E': /* encode */ l&=0xfff; l=golay(l); if (parity(l)) l^=0x800000l; printf("Codeword = %lX\n",l); break; case 'V': /* verify */ if (decode(0,&i,&l)) printf("Codeword %lX is not a Golay codeword.\n",l); else printf("Codeword %lX is a Golay codeword.\n",l); break; case 'C': /* correct */ g=l; /* save initial codeword */ j=decode(1,&i,&l); if ((j) && (i)) printf("Codeword %lX had %d bits corrected,\n" "resulting in codeword %lX with a parity error.\n",g,i,l); else if ((j == 0) && (i)) printf("Codeword %lX had %d bits corrected, resulting in codeword %lX.\n",g,i,l); else if ((j) && (i == 0)) printf("Codeword %lX has a parity error. No bits were corrected.\n",g); else if ((j == 0) && (i == 0)) printf("Codeword %lX does not require correction.\n",g); break; case 'T': /* test */ printf("Press SPACE for status, ESC to exit test...\n"); golay_test(); break; default: printf(errmsg); exit(0); } } /* end of G.C */ import java.util.*; import java.lang.*; import java.io.*; /* Name of the class has to be "Main" only if the class is public. */ class Ideone { public static void main (String[] args) throws java.lang.Exception { // your code goes here } }