From 2544b70216bb71aec663a9657142e13ad0c6ac41 Mon Sep 17 00:00:00 2001
From: "Roberto E. Vargas Caballero" <k0ga@shike2.net>
Date: Sat, 17 Jan 2026 10:57:43 +0100
Subject: [PATCH] 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             |  6 +++---
 tests/0045-dc.sh | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)
 create mode 100755 tests/0045-dc.sh

diff --git a/dc.c b/dc.c
index 092afc0..8017c58 100644
--- a/dc.c
+++ b/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;
diff --git a/tests/0045-dc.sh b/tests/0045-dc.sh
new file mode 100755
index 0000000..a4a22e1
--- /dev/null
+++ b/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