1 files changed, 21 insertions, 6 deletions

diff --git a/miscutils/dc.c b/miscutils/dc.c
index 0d09f5e2b..c7ce2be0b 100644
--- a/miscutils/dc.c
+++ b/miscutils/dc.c
@@ -35,10 +35,12 @@ enum { STACK_SIZE = (COMMON_BUFSIZE - offsetof(struct globals, stack)) / sizeof(
         base = 10; \
 } while (0)
 
-static void check_under(void)
+static unsigned check_under(void)
 {
-        if (pointer == 0)
+        unsigned p = pointer;
+        if (p == 0)
                 bb_error_msg_and_die("stack underflow");
+        return p - 1;
 }
 
 static void push(double a)
@@ -50,8 +52,9 @@ static void push(double a)
 
 static double pop(void)
 {
-        check_under();
-        return stack[--pointer];
+        unsigned p = check_under();
+        pointer = p;
+        return stack[p];
 }
 
 static void add(void)
@@ -91,6 +94,19 @@ static void mod(void)
 {
         data_t d = pop();
 
+        /* compat with dc (GNU bc 1.07.1) 1.4.1:
+         * $ dc -e '4 0 % p'
+         * dc: remainder by zero
+         * 0
+         */
+        if (d == 0) {
+                bb_error_msg("remainder by zero");
+                pop();
+                push(0);
+                return;
+        }
+        /* ^^^^ without this, we simply get SIGFPE and die */
+
         push((data_t) pop() % d);
 }
 
@@ -171,8 +187,7 @@ static void print_stack_no_pop(void)
 
 static void print_no_pop(void)
 {
-        check_under();
-        print_base(stack[pointer-1]);
+        print_base(stack[check_under()]);
 }
 
 struct op {