5d8f8570c
Denys Vlasenko
2023-06-26
Subject
shell/math: rename TOK_NUM to TOK_VALUE, improve comments
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shell/math.c+25 -24
| @@ -94,7 +94,6 @@ | |
| * | |
| * Merge in Aaron's comments previously posted to the busybox list, | |
| * modified slightly to take account of my changes to the code. | |
| - | * |
| */ | |
| /* | |
| * (C) 2003 Vladimir Oleynik <[email protected]> | |
| @@ -212,18 +211,18 @@ typedef unsigned char operator; | |
| #define TOK_UPLUS tok_decl(UNARYPREC+1,1) | |
| #define PREC_PRE (UNARYPREC+2) | |
| - | |
| #define TOK_PRE_INC tok_decl(PREC_PRE, 0) | |
| #define TOK_PRE_DEC tok_decl(PREC_PRE, 1) | |
| #define PREC_POST (UNARYPREC+3) | |
| - | |
| #define TOK_POST_INC tok_decl(PREC_POST, 0) | |
| #define TOK_POST_DEC tok_decl(PREC_POST, 1) | |
| - | #define SPEC_PREC (UNARYPREC+4) |
| - | |
| - | #define TOK_NUM tok_decl(SPEC_PREC, 0) |
| + | /* TOK_VALUE marks a number, name, name++/name--, or (EXPR): |
| + | * IOW: something which can be used as the left side of a binary op. |
| + | * Since it's never pushed to opstack, its precedence does not matter. |
| + | */ |
| + | #define TOK_VALUE tok_decl(PREC_POST, 2) |
| static int | |
| is_assign_op(operator op) | |
| @@ -625,7 +624,9 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| var_or_num_t *numstack, *numstackptr; | |
| /* Stack of operator tokens */ | |
| operator *opstack, *opstackptr; | |
| + | /* To detect whether we are after a "value": */ |
| operator lasttok; | |
| + | /* To insert implicit () in ?: ternary op: */ |
| operator insert_op = 0xff; | |
| unsigned ternary_level = 0; | |
| const char *errmsg; | |
| @@ -720,12 +721,12 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| } else { | |
| dbg("[%d] var:IGNORED", (int)(numstackptr - numstack)); | |
| expr = p; | |
| - | numstackptr->var_name = NULL; |
| - | numstackptr->val = 0; |
| + | numstackptr->var_name = NULL; /* not needed, paranoia */ |
| + | numstackptr->val = 0; /* not needed, paranoia */ |
| } | |
| - | push_num: |
| + | push_value: |
| numstackptr++; | |
| - | lasttok = TOK_NUM; |
| + | lasttok = TOK_VALUE; |
| continue; | |
| } | |
| @@ -747,7 +748,7 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| */ | |
| if (isalnum(*expr) || *expr == '_') | |
| goto syntax_err; | |
| - | goto push_num; |
| + | goto push_value; |
| } | |
| /* Should be an operator */ | |
| @@ -818,15 +819,14 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| dbg("insert_op=%02x op=%02x", insert_op, op); | |
| } | |
| tok_found1: | |
| - | /* post grammar: a++ reduce to num */ |
| - | if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC) |
| - | lasttok = TOK_NUM; |
| + | /* NAME++ is a "value" (something suitable for a binop) */ |
| + | if (PREC(lasttok) == PREC_POST) |
| + | lasttok = TOK_VALUE; |
| /* Plus and minus are binary (not unary) _only_ if the last | |
| - | * token was a number, or a right paren (which pretends to be |
| - | * a number, since it evaluates to one). Think about it. |
| - | * It makes sense. */ |
| - | if (lasttok != TOK_NUM) { |
| + | * token was a "value". Think about it. It makes sense. |
| + | */ |
| + | if (lasttok != TOK_VALUE) { |
| switch (op) { | |
| case TOK_ADD: | |
| //op = TOK_UPLUS; | |
| @@ -857,8 +857,8 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| prec = PREC(op); | |
| if (prec != PREC_LPAREN && prec < UNARYPREC) { | |
| /* binary, ternary or RPAREN */ | |
| - | if (lasttok != TOK_NUM) { |
| - | /* must be preceded by a num */ |
| + | if (lasttok != TOK_VALUE) { |
| + | /* must be preceded by a num (example?) */ |
| goto syntax_err; | |
| } | |
| /* if op is RPAREN: | |
| @@ -883,11 +883,12 @@ evaluate_string(arith_state_t *math_state, const char *expr) | |
| operator prev_op = *--opstackptr; | |
| if (op == TOK_RPAREN) { | |
| if (prev_op == TOK_LPAREN) { | |
| - | /* Erase var name: (var) is just a number, for example, (var) = 1 is not valid */ |
| + | /* Erase var name: for example, (VAR) = 1 is not valid */ |
| numstackptr[-1].var_name = NULL; | |
| - | /* Any operator directly after a |
| - | * close paren should consider itself binary */ |
| - | lasttok = TOK_NUM; |
| + | /* (EXPR) is a "value": next operator directly after |
| + | * close paren should be considered binary |
| + | */ |
| + | lasttok = TOK_VALUE; |
| goto next; | |
| } | |
| /* Not (y), but ...x~y). Fall through to evaluate x~y */ | |