str_mod: [nfc] rewrite in more modern C99 style

Upcoming changes will improve the efficiency of this function and decrease its
coupling with other operations. Rather than introduce these new changes in a
differing style, this preparatory commit rewrites the existing functionality in
this style first, without affecting its behavior. Related to #1873, #1998.

diff --git a/lib/expr/exeval.c b/lib/expr/exeval.c
index f3118b29af671befd1548c915b343596815ba461..3c272e1bfc5727e8bc2c455cef28ff213eb1a66d 100644 (file)
--- a/lib/expr/exeval.c
+++ b/lib/expr/exeval.c
@@ -691,15 +691,14 @@ static char *str_xor(Expr_t *ex, const char *l, const char *r) {
  * string mod
  */
 
-static char*
-str_mod(Expr_t* ex, char* l, char* r)
-{
-       int     c;
+static char *str_mod(Expr_t *ex, const char *l, const char *r) {
 
-       while ((c = *l++))
-               if (!strchr(r, c) && !strchr(l, c))
-                       sfputc(ex->tmp, c);
-       return exstash(ex->tmp, ex->ve);
+  for (const char *p = l; *p != '\0'; ++p) {
+    if (strchr(r, *p) == NULL && strchr(p + 1, *p) == NULL) {
+      sfputc(ex->tmp, *p);
+    }
+  }
+  return exstash(ex->tmp, ex->ve);
 }
 
 /*