shell/math.c: stop using bss variable

function                                             old     new   delta
evaluate_string                                        -     678    +678
expand_one_var                                      1543    1563     +20
builtin_type                                         114     116      +2
expand_and_evaluate_arith                             89      87      -2
prev_chk_var_recursive                                 4       -      -4
ash_arith                                            122     118      -4
arith_lookup_val                                     142     132     -10
arith                                                674      12    -662
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 2/4 up/down: 700/-682)           Total: 18 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

2 files changed, 37 insertions, 22 deletions

diff --git a/shell/math.c b/shell/math.c
index 555559a26..839715776 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -232,6 +232,7 @@ is_right_associative(operator prec)
                 || prec == PREC(TOK_CONDITIONAL));
 }
 
+
 typedef struct {
         arith_t val;
         arith_t contidional_second_val;
@@ -240,43 +241,49 @@ typedef struct {
                            else is variable name */
 } v_n_t;
 
-typedef struct chk_var_recursive_looped_t {
+typedef struct remembered_name {
+        struct remembered_name *next;
         const char *var;
-        struct chk_var_recursive_looped_t *next;
-} chk_var_recursive_looped_t;
+} remembered_name;
+
 
-static chk_var_recursive_looped_t *prev_chk_var_recursive;
+static arith_t FAST_FUNC
+evaluate_string(arith_state_t *math_state, const char *expr);
 
 static int
 arith_lookup_val(arith_state_t *math_state, v_n_t *t)
 {
         if (t->var) {
                 const char *p = lookupvar(t->var);
-
                 if (p) {
-                        chk_var_recursive_looped_t *cur;
-                        chk_var_recursive_looped_t cur_save;
+                        remembered_name *cur;
+                        remembered_name cur_save;
 
-                        /* recursively try p as expression */
-
-                        for (cur = prev_chk_var_recursive; cur; cur = cur->next) {
+                        /* did we already see this name?
+                         * testcase: a=b; b=a; echo $((a))
+                         */
+                        for (cur = math_state->list_of_recursed_names; cur; cur = cur->next) {
                                 if (strcmp(cur->var, t->var) == 0) {
-                                        /* expression recursion loop detected */
+                                        /* Yes. Expression recursion loop detected */
                                         return -5;
                                 }
                         }
-                        /* save current var name */
-                        cur = prev_chk_var_recursive;
+
+                        /* push current var name */
+                        cur = math_state->list_of_recursed_names;
                         cur_save.var = t->var;
                         cur_save.next = cur;
-                        prev_chk_var_recursive = &cur_save;
+                        math_state->list_of_recursed_names = &cur_save;
+
+                        /* recursively evaluate p as expression */
+                        t->val = evaluate_string(math_state, p);
+
+                        /* pop current var name */
+                        math_state->list_of_recursed_names = cur;
 
-                        t->val = arith(math_state, p);
-                        /* restore previous ptr after recursion */
-                        prev_chk_var_recursive = cur;
                         return math_state->errcode;
                 }
-                /* allow undefined var as 0 */
+                /* treat undefined var as 0 */
                 t->val = 0;
         }
         return 0;
@@ -487,8 +494,8 @@ endofname(const char *name)
         return name;
 }
 
-arith_t
-arith(arith_state_t *math_state, const char *expr)
+static arith_t FAST_FUNC
+evaluate_string(arith_state_t *math_state, const char *expr)
 {
         operator lasttok;
         int errcode;
@@ -677,6 +684,13 @@ arith(arith_state_t *math_state, const char *expr)
         return numstack->val;
 }
 
+arith_t FAST_FUNC
+arith(arith_state_t *math_state, const char *expr)
+{
+        math_state->list_of_recursed_names = NULL;
+        return evaluate_string(math_state, expr);
+}
+
 /*
  * Copyright (c) 1989, 1991, 1993, 1994
  *      The Regents of the University of California.  All rights reserved.
diff --git a/shell/math.h b/shell/math.h
index 9f3da7f59..e34b65d5d 100644
--- a/shell/math.h
+++ b/shell/math.h
@@ -95,13 +95,14 @@ typedef void        FAST_FUNC (*arith_var_set_t)(const char *name, const char *v
 //typedef const char* FAST_FUNC (*arith_var_endofname_t)(const char *name);
 
 typedef struct arith_state_t {
+        int                   errcode;
         arith_var_lookup_t    lookupvar;
         arith_var_set_t       setvar;
 //      arith_var_endofname_t endofname;
-        int                   errcode;
+        void                 *list_of_recursed_names;
 } arith_state_t;
 
-arith_t arith(arith_state_t *state, const char *expr);
+arith_t FAST_FUNC arith(arith_state_t *state, const char *expr);
 
 POP_SAVED_FUNCTION_VISIBILITY