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shell/math: rename TOK_NUM to TOK_VALUE, improve comments

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2023-06-26 09:59:56 +02:00
parent c1c267fd36
commit 5d8f8570c0
1 changed files with 25 additions and 24 deletions
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49
shell/math.c
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@ -94,7 +94,6 @@
* *
* Merge in Aaron's comments previously posted to the busybox list, * Merge in Aaron's comments previously posted to the busybox list,
* modified slightly to take account of my changes to the code. * modified slightly to take account of my changes to the code.
*
*/ */
/* /*
* (C) 2003 Vladimir Oleynik <dzo@simtreas.ru> * (C) 2003 Vladimir Oleynik <dzo@simtreas.ru>
@ -212,18 +211,18 @@ typedef unsigned char operator;
#define TOK_UPLUS tok_decl(UNARYPREC+1,1) #define TOK_UPLUS tok_decl(UNARYPREC+1,1)
#define PREC_PRE (UNARYPREC+2) #define PREC_PRE (UNARYPREC+2)
#define TOK_PRE_INC tok_decl(PREC_PRE, 0) #define TOK_PRE_INC tok_decl(PREC_PRE, 0)
#define TOK_PRE_DEC tok_decl(PREC_PRE, 1) #define TOK_PRE_DEC tok_decl(PREC_PRE, 1)
#define PREC_POST (UNARYPREC+3) #define PREC_POST (UNARYPREC+3)
#define TOK_POST_INC tok_decl(PREC_POST, 0) #define TOK_POST_INC tok_decl(PREC_POST, 0)
#define TOK_POST_DEC tok_decl(PREC_POST, 1) #define TOK_POST_DEC tok_decl(PREC_POST, 1)
#define SPEC_PREC (UNARYPREC+4) /* TOK_VALUE marks a number, name, name++/name--, or (EXPR):
* IOW: something which can be used as the left side of a binary op.
#define TOK_NUM tok_decl(SPEC_PREC, 0) * Since it's never pushed to opstack, its precedence does not matter.
*/
#define TOK_VALUE tok_decl(PREC_POST, 2)
static int static int
is_assign_op(operator op) 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; var_or_num_t *numstack, *numstackptr;
/* Stack of operator tokens */ /* Stack of operator tokens */
operator *opstack, *opstackptr; operator *opstack, *opstackptr;
/* To detect whether we are after a "value": */
operator lasttok; operator lasttok;
/* To insert implicit () in ?: ternary op: */
operator insert_op = 0xff; operator insert_op = 0xff;
unsigned ternary_level = 0; unsigned ternary_level = 0;
const char *errmsg; const char *errmsg;
@ -720,12 +721,12 @@ evaluate_string(arith_state_t *math_state, const char *expr)
} else { } else {
dbg("[%d] var:IGNORED", (int)(numstackptr - numstack)); dbg("[%d] var:IGNORED", (int)(numstackptr - numstack));
expr = p; expr = p;
numstackptr->var_name = NULL; numstackptr->var_name = NULL; /* not needed, paranoia */
numstackptr->val = 0; numstackptr->val = 0; /* not needed, paranoia */
} }
push_num: push_value:
numstackptr++; numstackptr++;
lasttok = TOK_NUM; lasttok = TOK_VALUE;
continue; continue;
} }
@ -747,7 +748,7 @@ evaluate_string(arith_state_t *math_state, const char *expr)
*/ */
if (isalnum(*expr) || *expr == '_') if (isalnum(*expr) || *expr == '_')
goto syntax_err; goto syntax_err;
goto push_num; goto push_value;
} }
/* Should be an operator */ /* 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); dbg("insert_op=%02x op=%02x", insert_op, op);
} }
tok_found1: tok_found1:
/* post grammar: a++ reduce to num */ /* NAME++ is a "value" (something suitable for a binop) */
if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC) if (PREC(lasttok) == PREC_POST)
lasttok = TOK_NUM; lasttok = TOK_VALUE;
/* Plus and minus are binary (not unary) _only_ if the last /* Plus and minus are binary (not unary) _only_ if the last
* token was a number, or a right paren (which pretends to be * token was a "value". Think about it. It makes sense.
* a number, since it evaluates to one). Think about it. */
* It makes sense. */ if (lasttok != TOK_VALUE) {
if (lasttok != TOK_NUM) {
switch (op) { switch (op) {
case TOK_ADD: case TOK_ADD:
//op = TOK_UPLUS; //op = TOK_UPLUS;
@ -857,8 +857,8 @@ evaluate_string(arith_state_t *math_state, const char *expr)
prec = PREC(op); prec = PREC(op);
if (prec != PREC_LPAREN && prec < UNARYPREC) { if (prec != PREC_LPAREN && prec < UNARYPREC) {
/* binary, ternary or RPAREN */ /* binary, ternary or RPAREN */
if (lasttok != TOK_NUM) { if (lasttok != TOK_VALUE) {
/* must be preceded by a num */ /* must be preceded by a num (example?) */
goto syntax_err; goto syntax_err;
} }
/* if op is RPAREN: /* if op is RPAREN:
@ -883,11 +883,12 @@ evaluate_string(arith_state_t *math_state, const char *expr)
operator prev_op = *--opstackptr; operator prev_op = *--opstackptr;
if (op == TOK_RPAREN) { if (op == TOK_RPAREN) {
if (prev_op == TOK_LPAREN) { 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; numstackptr[-1].var_name = NULL;
/* Any operator directly after a /* (EXPR) is a "value": next operator directly after
* close paren should consider itself binary */ * close paren should be considered binary
lasttok = TOK_NUM; */
lasttok = TOK_VALUE;
goto next; goto next;
} }
/* Not (y), but ...x~y). Fall through to evaluate x~y */ /* Not (y), but ...x~y). Fall through to evaluate x~y */