shell/math: change ?: nesting code to not have 63 level nesting limitation

function                                             old     new   delta
evaluate_string                                     1406    1432     +26
arith                                                 36      29      -7
arith_apply                                          998     990      -8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 26/-15)             Total: 11 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 21 insertions, 14 deletions

diff --git a/shell/math.c b/shell/math.c
index 6196a6ad9..3e339a5ec 100644
--- a/shell/math.c
+++ b/shell/math.c
@@ -599,8 +599,6 @@ static arith_t strto_arith_t(const char *nptr, char **endptr)
 static arith_t
 evaluate_string(arith_state_t *math_state, const char *expr)
 {
-#define EVAL_DISABLED ((unsigned long long)math_state->evaluation_disabled)
-#define TOP_BIT_ULL ((unsigned long long)LLONG_MAX + 1)
         operator lasttok;
         const char *errmsg = NULL;
         const char *start_expr = expr = skip_whitespace(expr);
@@ -617,6 +615,7 @@ evaluate_string(arith_state_t *math_state, const char *expr)
         operator *const opstack = alloca(expr_len * sizeof(opstack[0]));
         operator *opstackptr = opstack;
         operator insert_op = 0xff;
+        unsigned ternary_level = 0;
 
         /* Start with a left paren */
         dbg("(%d) op:TOK_LPAREN", (int)(opstackptr - opstack));
@@ -875,8 +874,11 @@ dbg("    numstack:%d val:%lld '%s'", (int)(numstackptr - numstack), numstackptr[
                                         /* Example: a=1?2:3,a. We just executed ":".
                                          * Prevent assignment from being still disabled.
                                          */
-                                        math_state->evaluation_disabled >>= 1;
-                                        dbg("':' executed: evaluation_disabled=%llx (restored)", EVAL_DISABLED);
+                                        if (ternary_level == math_state->evaluation_disabled) {
+                                                math_state->evaluation_disabled = 0;
+                                                dbg("':' executed: evaluation_disabled=CLEAR");
+                                        }
+                                        ternary_level--;
                                 }
                         } /* while (opstack not empty) */
 
@@ -887,12 +889,11 @@ dbg("    numstack:%d val:%lld '%s'", (int)(numstackptr - numstack), numstackptr[
                                 /* We just now evaluated EXPR before "?".
                                  * Should we disable evaluation now?
                                  */
-                                if (math_state->evaluation_disabled & TOP_BIT_ULL)
-                                        goto err; /* >63 levels of ?: nesting not supported */
-                                math_state->evaluation_disabled =
-                                        (math_state->evaluation_disabled << 1)
-                                        | (numstackptr[-1].val == 0);
-                                dbg("'?' entered: evaluation_disabled=%llx", EVAL_DISABLED);
+                                ternary_level++;
+                                if (numstackptr[-1].val == 0 && !math_state->evaluation_disabled) {
+                                        math_state->evaluation_disabled = ternary_level;
+                                        dbg("'?' entered: evaluation_disabled=%u", math_state->evaluation_disabled);
+                                }
                         }
                 } /* if */
                 /* else: LPAREN or UNARY: push it on opstack */
@@ -906,9 +907,15 @@ dbg("    numstack:%d val:%lld '%s'", (int)(numstackptr - numstack), numstackptr[
                         insert_op = 0xff;
                         dbg("inserting %02x", op);
                         if (op == TOK_CONDITIONAL_SEP) {
-                                /* The next token is ":". Toggle "do not evaluate" bit */
-                                math_state->evaluation_disabled ^= 1;
-                                dbg("':' entered: evaluation_disabled=%llx (negated)", EVAL_DISABLED);
+                                /* The next token is ":". Toggle "do not evaluate" state */
+                                if (!math_state->evaluation_disabled) {
+                                        math_state->evaluation_disabled = ternary_level;
+                                        dbg("':' entered: evaluation_disabled=%u", math_state->evaluation_disabled);
+                                } else if (ternary_level == math_state->evaluation_disabled) {
+                                        math_state->evaluation_disabled = 0;
+                                        dbg("':' entered: evaluation_disabled=CLEAR");
+                                } /* else: ternary_level > nonzero evaluation_disabled: we are in nested ?:, in its disabled branch */
+                                        /* do nothing */
                         }
                         goto tok_found1;
                 }
diff --git a/shell/math.h b/shell/math.h
index 9812184f1..439031828 100644
--- a/shell/math.h
+++ b/shell/math.h
@@ -57,7 +57,7 @@ typedef const char* FAST_FUNC (*arith_var_lookup_t)(const char *name);
 typedef void        FAST_FUNC (*arith_var_set_t)(const char *name, const char *val);
 
 typedef struct arith_state_t {
-        uint64_t              evaluation_disabled;
+        unsigned              evaluation_disabled;
         const char           *errmsg;
         void                 *list_of_recursed_names;
         arith_var_lookup_t    lookupvar;