Add 2020 source files for real

2020/kurdyukov4/rand.c

@@ -0,0 +1,47 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+main(int c, char *v[]) {
+	FILE * f;
+	int flen, ctxt, osize, pos, npos, i, k, l;
+	char * m, *loc;
+	char a;
+	if (c != 5) exit(1);
+	f = fopen(v[1], "r");
+	if (!f) exit(1);
+	osize = atoi(v[2]);
+	ctxt = atoi(v[3]);
+	srandom(atoi(v[4]));
+	fseek(f, 0, SEEK_END); flen = ftell(f); fseek(f, 0, SEEK_SET);
+	if (ctxt < 1 || ctxt >= flen) exit(1);
+
+	m = malloc(flen + flen + ctxt);
+	if (!m) exit(1);
+	fread(m, flen, 1, f);
+
+     for (i = k = l = 0; i < flen;)
+        if ('_' - (a = m[i++]))
+          {
+            if (a == '<')
+              for (a = ' '; i < flen && m[i++] - '>';);;
+            if ((a - ' ' && a - '\n' &&
+                 a - '\r' && a - '\t') || k - (a = ' '))
+              m[l++] = k = a;
+          };
+      flen = l;
+
+	memcpy(m+flen, m, flen + ctxt);
+	pos = random() % flen;
+	for (i = 0; i < osize; ++i) {
+		npos = random() % flen;
+		// find the context at pos starting from npos
+		loc = memmem(m+npos, flen+ctxt-1, m+pos, ctxt);
+		if (!loc) puts("I'm lost!!!"), exit(1);
+		npos = (loc-m) % flen;
+		putchar(m[npos]);
+		pos = npos+1;
+	}
+	putchar('\n');
+}
+