Thanks to John Cummings.

src/cmd/upas/bayes/regen.c

@@ -0,0 +1,176 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <regexp.h>
+#include "dfa.h"
+
+/***
+ * Regular expression for matching.
+ */
+
+char *ignore[] = 
+{
+	/* HTML that isn't A, IMG, or FONT */
+	/* Must have a space somewhere to avoid catching <email@address> */
+	"<[ 	\n\r]*("
+		"[^aif]|"
+		"a[^> \t\r\n]|"
+		"i[^mM \t\r\n]|"
+		"im[^gG \t\r\n]|"
+		"img[^> \t\r\n]|"
+		"f[^oO \t\r\n]|"
+		"fo[^Nn \t\r\n]|"
+		"fon[^tT \t\r\n]|"
+		"font[^> \r\t\n]"
+	")[^>]*[ \t\n\r][^>]*>",
+	"<[ 	\n\r]*("
+		"i|im|f|fo|fon"
+	")[ \t\r\n][^>]*>",
+
+	/* ignore html comments */
+	"<!--([^\\-]|-[^\\-]|--[^>]|\n)*-->",
+
+	/* random mail strings */
+	"^message-id:.*\n([ 	].*\n)*",
+	"^in-reply-to:.*\n([ 	].*\n)*",
+	"^references:.*\n([ 	].*\n)*",
+	"^date:.*\n([ 	].*\n)*",
+	"^delivery-date:.*\n([ 	].*\n)*",
+	"e?smtp id .*",
+	"^	id.*",
+	"boundary=.*",
+	"name=\"",
+	"filename=\"",
+	"news:<[^>]+>",
+	"^--[^ 	]*$",
+
+	/* base64 encoding */
+	"^[0-9a-zA-Z+\\-=/]+$",
+
+	/* uu encoding */
+	"^[!-Z]+$",
+
+	/* little things */
+	".",
+	"\n",
+};
+
+char *keywords[] =
+{
+	"([a-zA-Z'`$!¡-￿]|[0-9]([.,][0-9])*)+",
+};
+
+int debug;
+
+Dreprog*
+dregcomp(char *buf)
+{
+	Reprog *r;
+	Dreprog *d;
+
+	if(debug)
+		print(">>> '%s'\n", buf);
+
+	r = regcomp(buf);
+	if(r == nil)
+		sysfatal("regcomp");
+	d = dregcvt(r);
+	if(d == nil)
+		sysfatal("dregcomp");
+	free(r);
+	return d;
+}
+
+char*
+strcpycase(char *d, char *s)
+{
+	int cc, esc;
+
+	cc = 0;
+	esc = 0;
+	while(*s){
+		if(*s == '[')
+			cc++;
+		if(*s == ']')
+			cc--;
+		if(!cc && 'a' <= *s && *s <= 'z'){
+			*d++ = '[';
+			*d++ = *s;
+			*d++ = *s+'A'-'a';
+			*d++ = ']';
+		}else
+			*d++ = *s;
+		if(*s == '\\')
+			esc++;
+		else if(esc)
+			esc--;
+		s++;
+	}
+	return d;
+}
+
+void
+regerror(char *msg)
+{
+	sysfatal("regerror: %s", msg);
+}
+
+void
+buildre(Dreprog *re[3])
+{
+	int i;
+	static char buf[16384], *s;
+
+	re[0] = dregcomp("^From ");
+	
+	s = buf;
+	for(i=0; i<nelem(keywords); i++){
+		if(i != 0)
+			*s++ = '|';
+		s = strcpycase(s, keywords[i]);
+	}
+	*s = 0;
+	re[1] = dregcomp(buf);
+
+	s = buf;
+	for(i=0; i<nelem(ignore); i++){
+		if(i != 0)
+			*s++ = '|';
+		s = strcpycase(s, ignore[i]);
+	}
+	*s = 0;
+	re[2] = dregcomp(buf);
+}
+
+void
+usage(void)
+{
+	fprint(2, "usage: regen [-d]\n");
+	exits("usage");
+}
+
+void
+main(int argc, char **argv)
+{
+	Dreprog *re[3];
+	Biobuf b;
+
+	ARGBEGIN{
+	default:
+		usage();
+	case 'd':
+		debug = 1;
+	}ARGEND
+
+	if(argc != 0)
+		usage();
+
+	buildre(re);
+	Binit(&b, 1, OWRITE);
+	Bprintdfa(&b, re[0]);
+	Bprintdfa(&b, re[1]);
+	Bprintdfa(&b, re[2]);
+	exits(0);
+}
+
+