dc: Relax tail call optimization

Classical dc implementations only apply tail recursion optimization
but we were applying tail call recursion, removing one frame even
when no recursion was involved. This creates problems with bc that
does not track this optimization and it generates values for the Q
command without caring about this optimization.

dc.c

@@ -1892,14 +1892,14 @@ execmacro(void)
 		return;
 	}
 
-	/* check for tail recursion */
-	for (ch = *input->s; ch > 0 && ch < UCHAR_MAX; ch = *input->s) {
+	for (ch = *input->s; ch > 0 && ch <= UCHAR_MAX; ch = *input->s) {
 		if (!isspace(ch))
 			break;
 		++input->s;
 	}
 
-	if (ch == '\0') {
+	/* check for tail recursion */
+	if (ch == '\0' && strcmp(input->buf, v.u.s) == 0) {
 		free(input->buf);
 		input->buf = input->s = v.u.s;
 		return;

tests/0045-dc.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+set -e
+
+tmp=$$.tmp
+
+trap 'rm -f $tmp' EXIT
+trap 'exit $?' HUP INT TERM
+
+echo 0 > $tmp
+
+../dc -i <<'EOF' | diff -u - $tmp
+[ 0 Lxs. 2Q]s<128>
+[ .7853981633974483096156608458198757210492923498437764 1/ Lxs. 3Q]s<130>
+[K 52><130> ]s<129>
+[Sxlx 0=<128> lx 1=<129> 0 Lxs. 1Q]s<1>
+
+ 1l<1>xps.
+EOF