Scrap readrune(), introducing fgetrune()

Interface as proposed by cls, but internally rewritten after a few
considerations.
The code is much shorter and to the point, aligning itself with other
standard functions. It should also be much faster, which is not bad.

libutf/fgetrune.c

@@ -0,0 +1,34 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "../utf.h"
+
+int
+fgetrune(Rune *p, FILE *fp)
+{
+	char buf[UTFmax];
+	int i;
+
+	for (i = 0; i < UTFmax && (buf[i] = fgetc(fp)) != EOF && ++i ;)
+		if (charntorune(p, buf, i) > 0)
+			break;
+	if (ferror(fp))
+		return -1;
+
+	return i;
+}
+
+int
+efgetrune(Rune *p, FILE *fp, const char *file)
+{
+	int ret;
+
+	if ((ret = fgetrune(p, fp)) < 0) {
+		fprintf(stderr, "fgetrune %s: %s\n", file, strerror(errno));
+		exit(1);
+	}
+	return ret;
+}

libutf/readrune.c

@@ -1,47 +0,0 @@
-/* See LICENSE file for copyright and license details. */
-#include <errno.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-#include "../utf.h"
-
-int
-readrune(const char *file, FILE *fp, Rune *r)
-{
-	char buf[UTFmax];
-	int c, i;
-
-	if ((c = fgetc(fp)) == EOF) {
-		if (ferror(fp)) {
-			fprintf(stderr, "%s: read error: %s\n",
-				file, strerror(errno));
-			exit(1);
-		}
-		return 0;
-	}
-
-	if (c < Runeself) {
-		*r = (Rune)c;
-		return 1;
-	}
-
-	buf[0] = c;
-	for (i = 1; i < UTFmax; ) {
-		if ((c = fgetc(fp)) == EOF) {
-			if (ferror(fp)) {
-				fprintf(stderr, "%s: read error: %s\n",
-					file, strerror(errno));
-				exit(1);
-			}
-			*r = Runeerror;
-			return i;
-		}
-		buf[i++] = c;
-		if (fullrune(buf, i)) {
-			chartorune(r, buf);
-			break;
-		}
-	}
-	return i;
-}