Initial

markov/make

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+cc=gcc
+exe=markov
+
+$cc -o $exe src/markov.c

markov/src/markov.c

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+/* Copyright (C) 1999 Lucent Technologies */
+/* Excerpted from 'The Practice of Programming' */
+/* by Brian W. Kernighan and Rob Pike */
+
+/*
+ * Markov chain random text generator.
+ */
+
+#include "markov.h"
+
+enum {
+	NPREF	= 2,	/* number of prefix words */
+	NHASH	= 14386,	/* size of state hash table array */
+	MAXGEN	= 400	/* maximum words generated */
+};
+
+typedef struct State State;
+typedef struct Suffix Suffix;
+
+struct State {	/* prefix + suffix list */
+	char	*pref[NPREF];	/* prefix words */
+	Suffix	*suf;			/* list of suffixes */
+	State	*next;			/* next in hash table */
+};
+
+struct Suffix {	/* list of suffixes */
+	char	*word;			/* suffix */
+	Suffix	*next;			/* next in list of suffixes */
+};
+
+State	*lookup(char *prefix[], int create);
+void	build(char *prefix[], FILE*);
+void	generate(int nwords, char *prefixOne, char *prefixTwo);
+void	add(char *prefix[], char *word);
+
+State	*statetab[NHASH];	/* hash table of states */
+
+char NONWORD[] = "\n";  /* cannot appear as real word */
+
+/* markov main: markov-chain random text generation */
+int main(int argc, char **argv)
+{
+    char *one = argv[1];
+    char *two = argv[2];
+
+	int i, nwords = MAXGEN;
+	char *prefix[NPREF];		/* current input prefix */
+
+	int c;
+	long seed;
+
+	//setprogname("markov");
+	seed = time(NULL);
+
+	srand(seed);
+	for (i = 0; i < NPREF; i++)	/* set up initial prefix */
+		prefix[i] = NONWORD;
+
+	build(prefix, stdin);
+	add(prefix, NONWORD);
+	generate(nwords, one, two);
+	return 0;
+}   
+
+const int MULTIPLIER = 31;  /* for hash() */
+
+/* hash: compute hash value for array of NPREF strings */
+unsigned int hash(char *s[NPREF])
+{
+	unsigned int h;
+	unsigned char *p;
+	int i;
+
+	h = 0;
+	for (i = 0; i < NPREF; i++)
+		for (p = (unsigned char *) s[i]; *p != '\0'; p++)
+			h = MULTIPLIER * h + *p;
+	return h % NHASH;
+}
+
+/* lookup: search for prefix; create if requested. */
+/*  returns pointer if present or created; NULL if not. */
+/*  creation doesn't strdup so strings mustn't change later. */
+State* lookup(char *prefix[NPREF], int create)
+{
+	int i, h;
+	State *sp;
+
+	h = hash(prefix);
+	for (sp = statetab[h]; sp != NULL; sp = sp->next) {
+		for (i = 0; i < NPREF; i++)
+			if (strcmp(prefix[i], sp->pref[i]) != 0)
+				break;
+		if (i == NPREF)		/* found it */
+			return sp;
+	}
+	if (create) {
+		sp = (State *) malloc(sizeof(State));
+		for (i = 0; i < NPREF; i++)
+			sp->pref[i] = prefix[i];
+		sp->suf = NULL;
+		sp->next = statetab[h];
+		statetab[h] = sp;
+	}
+	return sp;
+}
+
+/* addsuffix: add to state. suffix must not change later */
+void addsuffix(State *sp, char *suffix)
+{
+	Suffix *suf;
+
+	suf = (Suffix *) malloc(sizeof(Suffix));
+	suf->word = suffix;
+	suf->next = sp->suf;
+	sp->suf = suf;
+}
+
+/* add: add word to suffix list, update prefix */
+void add(char *prefix[NPREF], char *suffix)
+{
+	State *sp;
+
+	sp = lookup(prefix, 1);  /* create if not found */
+	addsuffix(sp, suffix);
+	/* move the words down the prefix */
+	memmove(prefix, prefix+1, (NPREF-1)*sizeof(prefix[0]));
+	prefix[NPREF-1] = suffix;
+}
+
+/* build: read input, build prefix table */
+void build(char *prefix[NPREF], FILE *f)
+{
+	char buf[100], fmt[10];
+
+	/* create a format string; %s could overflow buf */
+	sprintf(fmt, "%%%ds", sizeof(buf)-1);
+	while (fscanf(f, fmt, buf) != EOF)
+		add(prefix, strdup(buf));
+}
+
+/* generate: produce output, one word per line */
+void generate(int nwords, char *prefixOne, char *prefixTwo)
+{
+	State *sp;
+	Suffix *suf;
+	char *prefix[NPREF], *w;
+	int i, nmatch;
+
+	for (i = 0; i < NPREF; i++)	/* reset initial prefix */
+		prefix[i] = NONWORD;
+
+    prefix[0] = prefixOne;
+    prefix[1] = prefixTwo;
+
+	for (i = 0; i < nwords; i++) {
+		sp = lookup(prefix, 0);
+		if (sp == NULL) {
+			printf("internal error: lookup failed");
+            exit(1);
+        }
+
+		nmatch = 0;
+		for (suf = sp->suf; suf != NULL; suf = suf->next)
+			if (rand() % ++nmatch == 0) /* prob = 1/nmatch */
+				w = suf->word;
+		if (nmatch == 0)
+			printf("internal error: no suffix %d %s", i, prefix[0]);
+		if (strcmp(w, NONWORD) == 0)
+			break;
+		printf("%s ", w);
+		memmove(prefix, prefix+1, (NPREF-1)*sizeof(prefix[0]));
+		prefix[NPREF-1] = w;
+	}
+}

markov/src/markov.h

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