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996
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1 /*
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2 * a crude implementation of a trigger interpreter.
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3 *
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4 * Author: Bertram Felgenhauer (aka int-e), 2005-07-26,27
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5 */
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6 #include <stdio.h>
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7 #include <stdlib.h>
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8 #include <time.h>
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9
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10 unsigned char prog[1048576];
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11 unsigned char trigger[256];
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12
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13 int main(int argc, char **argv)
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14 {
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15 int pc = 0, max, bits=0, input=0;
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16 FILE *in;
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17
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18 srand(time(NULL));
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19
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20 if (argc<2) {
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21 fprintf(stderr, "Usage: %s program [input]\n", argv[0]);
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22 exit(1);
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23 }
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24 in = fopen(argv[1], "r");
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25 if (!in) {
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26 fprintf(stderr, "Could not open '%s'.", argv[1]);
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27 exit(1);
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28 }
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29 max = fread(prog, 1, sizeof(prog), in);
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30 fclose(in);
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31 in = NULL;
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32 input = EOF;
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33 if (argc>2) {
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34 in = fopen(argv[2], "r");
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35 }
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36 if (max == sizeof(prog)) {
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37 fprintf(stderr, "Warning: only the first %d bytes of the program "
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38 "were read.", sizeof(prog));
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39 }
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40 while (pc<max) {
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41 if (pc<max-1 && prog[pc] == prog[pc+1]) {
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42 if (pc<max-2 && prog[pc] == prog[pc+2]) {
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43 if (pc<max-3 && prog[pc] == prog[pc+3]) {
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44 /* AAAA pattern -> input */
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45 if (!bits) {
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46 if (in)
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47 input = getc(in);
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48 bits = 8;
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49 }
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50 if (input != EOF) {
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51 bits--;
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52 trigger[prog[pc]] = !!(input & (1<<bits));
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53 }
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54 pc += 4;
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55 } else {
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56 /* AAA pattern -> output */
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57 putchar(prog[pc]);
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58 pc += 3;
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59 }
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60 } else {
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61 /* AAB pattern -> conditional jump */
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62 if (pc>max-3) {
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63 /* just AA at end of program -- exit silently */
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64 return 0;
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65 }
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66 if (trigger[prog[pc]]) {
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67 /* jump */
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68 int nxt = pc+3;
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69 int prv = pc-1;
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70 for ( ; ; nxt++, prv--) {
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71 int l = prv >= 0 && prog[pc+2] == prog[prv];
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72 int r = nxt < max && prog[pc+2] == prog[nxt];
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73
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74 if (l && (!r || rand()/(RAND_MAX/2))) {
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75 pc = prv;
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76 break;
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77 } else if (r) {
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78 pc = nxt;
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79 break;
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80 }
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81 if (nxt >= max && prv < 0) {
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82 /* label not found */
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83 pc += 3;
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84 break;
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85 }
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86 }
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87 } else {
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88 /* skip */
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89 pc += 3;
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90 }
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91 }
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92 } else {
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93 /* A pattern -> toggle */
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94 trigger[prog[pc]] ^= 1;
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95 pc++;
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96 }
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97 }
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98 return 0;
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99 }
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