dc(1): properly report errors

[kshe]

Hi,

On error, the BN functions do not set errno, so errx(3) should be used
instead of err(3).  Moreover, one may call ERR_reason_error_string(3) to
obtain a real error message from an error code.

        $ dc -e '2 2 64^^'
        dc: big number failure 3fff072: Undefined error: 0

        $ ./dc -e '2 2 64^^'
        dc: BN failure: bignum too long

Index: mem.c
===================================================================
RCS file: /cvs/src/usr.bin/dc/mem.c,v
retrieving revision 1.9
diff -u -p -r1.9 mem.c
--- mem.c       12 Dec 2017 19:08:57 -0000      1.9
+++ mem.c       15 Dec 2017 09:35:48 -0000
@@ -91,13 +91,19 @@ bstrdup(const char *p)
 void
 bn_check(int x)
 {
-       if (x == 0)
-               err(1, "big number failure %lx", ERR_get_error());
+       if (x == 0) {
+               ERR_load_BN_strings();
+               errx(1, "BN failure: %s",
+                   ERR_reason_error_string(ERR_get_error()));
+       }
 }
 
 void
 bn_checkp(const void *p)
 {
-       if (p == NULL)
-               err(1, "allocation failure %lx", ERR_get_error());
+       if (p == NULL) {
+               ERR_load_BN_strings();
+               errx(1, "BN failure: %s",
+                   ERR_reason_error_string(ERR_get_error()));
+       }
 }

Regards,

kshe