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Clean up preprocessor expression evaluation code

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Remove redundant code and add/improve comments.
This commit is contained in:
Olly Betts 2022-02-24 08:15:07 +13:00
commit 81caed4f1d
1 changed files with 34 additions and 16 deletions
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50
Source/Preprocessor/expr.c
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@ -18,8 +18,19 @@
static Scanner *scan = 0;
typedef struct {
/* One of the EXPR_xxx values defined below. */
int op;
/* op == EXPR_OP: value is the token specifying which operator.
*
* op == EXPR_VALUE && svalue == NULL: Numeric expression value.
*
* Otherwise unused.
*/
long value;
/* op == EXPR_VALUE: If non-NULL, string expression value; if NULL see value.
*
* Otherwise unused.
*/
String *svalue;
} exprval;
@ -27,7 +38,11 @@ typedef struct {
#define EXPR_VALUE 2
#define EXPR_OP 3
#define EXPR_GROUP 4
#define EXPR_UMINUS 100
/* Special token value used here to distinguish from SWIG_TOKEN_MINUS
* (which we use here for a two argument minus).
*/
#define OP_UMINUS 100
static exprval stack[256]; /* Parsing stack */
static int sp = 0; /* Stack pointer */
@ -38,7 +53,7 @@ static const char *errmsg = 0; /* Parsing error */
/* Initialize the precedence table for various operators. Low values have higher precedence */
static void init_precedence() {
prec[SWIG_TOKEN_NOT] = 10;
prec[EXPR_UMINUS] = 10;
prec[OP_UMINUS] = 10;
prec[SWIG_TOKEN_STAR] = 20;
prec[SWIG_TOKEN_SLASH] = 20;
prec[SWIG_TOKEN_PERCENT] = 20;
@ -63,7 +78,7 @@ static void init_precedence() {
#define UNARY_OP(token) (((token) == SWIG_TOKEN_NOT) || \
((token) == SWIG_TOKEN_LNOT) || \
((token) == EXPR_UMINUS))
((token) == OP_UMINUS))
/* Reduce a single operator on the stack */
/* return 0 on failure, 1 on success */
@ -183,7 +198,7 @@ static int reduce_op() {
stack[sp - 1].value = !stack[sp].value;
sp--;
break;
case EXPR_UMINUS:
case OP_UMINUS:
stack[sp - 1].value = -stack[sp].value;
sp--;
break;
@ -278,13 +293,15 @@ int Preprocessor_expr(DOH *s, int *error) {
/* Put initial state onto the stack */
stack[sp].op = EXPR_TOP;
stack[sp].value = 0;
while (1) {
/* Look at the top of the stack */
switch (stack[sp].op) {
case EXPR_TOP:
/* An expression. Can be a number or another expression enclosed in parens */
/* EXPR_TOP is a place-holder which can only appear on the top of the
* stack. We can reduce it to any expression - a number, a string, an
* unary operator, or another expression enclosed in parentheses.
*/
token = expr_token(scan);
if (!token) {
errmsg = "Expected an expression";
@ -296,26 +313,27 @@ int Preprocessor_expr(DOH *s, int *error) {
char *c = Char(Scanner_text(scan));
stack[sp].value = (long) strtol(c, 0, 0);
stack[sp].svalue = 0;
/* stack[sp].value = (long) atol(Char(Scanner_text(scan))); */
stack[sp].op = EXPR_VALUE;
} else if (token == SWIG_TOKEN_PLUS) {
} else if ((token == SWIG_TOKEN_MINUS) || (token == SWIG_TOKEN_LNOT) || (token == SWIG_TOKEN_NOT)) {
if (token == SWIG_TOKEN_MINUS)
token = EXPR_UMINUS;
token = OP_UMINUS;
stack[sp].value = token;
stack[sp++].op = EXPR_OP;
stack[sp].op = EXPR_OP;
sp++;
stack[sp].op = EXPR_TOP;
stack[sp].svalue = 0;
} else if (token == SWIG_TOKEN_LPAREN) {
stack[sp++].op = EXPR_GROUP;
stack[sp].op = EXPR_GROUP;
sp++;
stack[sp].op = EXPR_TOP;
stack[sp].value = 0;
stack[sp].svalue = 0;
} else if (token == SWIG_TOKEN_ENDLINE) {
} else if (token == SWIG_TOKEN_STRING) {
stack[sp].svalue = NewString(Scanner_text(scan));
stack[sp].op = EXPR_VALUE;
} else if (token == SWIG_TOKEN_ID) {
/* Defined macros have been expanded already so this is an unknown
* macro, which gets treated as zero.
*/
stack[sp].value = 0;
stack[sp].svalue = 0;
stack[sp].op = EXPR_VALUE;
@ -327,7 +345,9 @@ int Preprocessor_expr(DOH *s, int *error) {
goto syntax_error;
break;
case EXPR_VALUE:
/* A value is on the stack. We may reduce or evaluate depending on what the next token is */
/* A value is on top of the stack. We may reduce or evaluate depending
* on what the next token is.
*/
token = expr_token(scan);
if (!token) {
/* End of input. Might have to reduce if an operator is on stack */
@ -371,7 +391,6 @@ int Preprocessor_expr(DOH *s, int *error) {
stack[sp].value = token;
sp++;
stack[sp].op = EXPR_TOP;
stack[sp].value = 0;
} else {
if (stack[sp - 1].op != EXPR_OP)
goto syntax_error_expected_operator;
@ -390,7 +409,6 @@ int Preprocessor_expr(DOH *s, int *error) {
stack[sp].value = token;
sp++;
stack[sp].op = EXPR_TOP;
stack[sp].value = 0;
}
break;
case SWIG_TOKEN_RPAREN: