[LTP] [PATCH v4 1/2] lib: Add generic boolean expression parser and eval
Cyril Hrubis
chrubis@suse.cz
Tue Nov 3 17:10:51 CET 2020
Add a simple and generic boolean expression parser and evaluator. This
is a first step in order to implement more complex kconfig expressions,
but since we are likely to reuse the parser for other purposes in the
future it's implemented as a generic boolean parser.
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
---
v4:
- struct tst_expr is now trailing array
- pointer in tst_expr renamed from expr to rpn
- pass just pointer to the array to the tokenize() function
include/tst_bool_expr.h | 85 +++++++
lib/newlib_tests/.gitignore | 1 +
lib/newlib_tests/tst_bool_expr.c | 128 ++++++++++
lib/tst_bool_expr.c | 398 +++++++++++++++++++++++++++++++
4 files changed, 612 insertions(+)
create mode 100644 include/tst_bool_expr.h
create mode 100644 lib/newlib_tests/tst_bool_expr.c
create mode 100644 lib/tst_bool_expr.c
diff --git a/include/tst_bool_expr.h b/include/tst_bool_expr.h
new file mode 100644
index 000000000..894d21954
--- /dev/null
+++ b/include/tst_bool_expr.h
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2020 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+#ifndef TST_BOOL_EXPR_H__
+#define TST_BOOL_EXPR_H__
+
+enum tst_op {
+ TST_OP_NOT,
+ TST_OP_AND,
+ TST_OP_OR,
+ TST_OP_VAR,
+ /* Used only internally */
+ TST_OP_LPAR,
+ TST_OP_RPAR,
+};
+
+struct tst_expr_tok {
+ enum tst_op op;
+ const char *tok;
+ size_t tok_len;
+ struct tst_expr_tok *next;
+ const void *priv;
+};
+
+struct tst_expr {
+ struct tst_expr_tok *rpn;
+ struct tst_expr_tok buf[];
+};
+
+/*
+ * Parses an boolean expression and returns a simplified RPN version.
+ *
+ * If expression is not valid the call prints error into stderr and returns
+ * NULL. On success pointer to an expression is returned which can be evaluated
+ * by the tst_bool_expr_eval() function and has to be later freed by the
+ * caller.
+ *
+ * The boolean expression can consists of:
+ *
+ * - unary negation opeartion !
+ * - two binary operations & and |
+ * - correct sequence of parentheses ()
+ * - strings that are treated as boolean variables
+ *
+ * e.g. '(A | B) & C' or 'Variable_1 & Variable_2' are both a valid boolean
+ * expressions.
+ *
+ * @expr String containing a boolean expression to be parsed.
+ * @return Pointer to an RPN expression.
+ */
+struct tst_expr *tst_bool_expr_parse(const char *expr);
+
+/*
+ * Prints an string representation of the expression into a FILE.
+ *
+ * @param A FILE to print to.
+ * @expr An expression to print.
+ */
+void tst_bool_expr_print(FILE *f, struct tst_expr *expr);
+
+/*
+ * Evaluates an expression given a map for variables.
+ *
+ * The call will fail if:
+ * - map function returns -1 which indicates undefined variable
+ * - the eval function runs out of stack
+ *
+ * @param expr Boolean expression in RPN.
+ * @param map Mapping function for boolean variables.
+ *
+ * @return Returns 0 or 1 if expression was evaluated correctly and -1 on error.
+ */
+int tst_bool_expr_eval(struct tst_expr *expr,
+ int (*map)(struct tst_expr_tok *var));
+
+/*
+ * Frees the memory allocated by the tst_bool_expr_parse().
+ *
+ * @param Boolean expression.
+ */
+void tst_bool_expr_free(struct tst_expr *expr);
+
+#endif /* TST_BOOL_EXPR_H__ */
diff --git a/lib/newlib_tests/.gitignore b/lib/newlib_tests/.gitignore
index 44bc6526f..1e96db1da 100644
--- a/lib/newlib_tests/.gitignore
+++ b/lib/newlib_tests/.gitignore
@@ -33,3 +33,4 @@ test_exec_child
test_kconfig
variant
test_guarded_buf
+tst_bool_expr
diff --git a/lib/newlib_tests/tst_bool_expr.c b/lib/newlib_tests/tst_bool_expr.c
new file mode 100644
index 000000000..f9bb1780d
--- /dev/null
+++ b/lib/newlib_tests/tst_bool_expr.c
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2017 Cyril Hrubis <chrubis@suse.cz>
+ */
+
+/*
+ * Basic unit test for the bolean expression parser and evaluator.
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include "tst_test.h"
+#include "tst_bool_expr.h"
+
+static int a, b, c;
+
+static int map(struct tst_expr_tok *var)
+{
+ if (!strncmp(var->tok, "A", var->tok_len))
+ return a;
+
+ if (!strncmp(var->tok, "B", var->tok_len))
+ return b;
+
+ if (!strncmp(var->tok, "C", var->tok_len))
+ return c;
+
+ if (!strncmp(var->tok, "True", var->tok_len))
+ return 1;
+
+ if (!strncmp(var->tok, "False", var->tok_len))
+ return 0;
+
+ return -1;
+}
+
+static void parse_fail(const char *expr)
+{
+ struct tst_expr *res;
+
+ tst_res(TINFO, "Parsing '%s'", expr);
+
+ res = tst_bool_expr_parse(expr);
+
+ if (res) {
+ printf("In RPN: ");
+ tst_bool_expr_print(stdout, res);
+ printf("\n");
+ tst_bool_expr_free(res);
+ tst_res(TFAIL, "Expression was parsed");
+ } else {
+ tst_res(TPASS, "Parser returned an error");
+ }
+}
+
+static void do_eval_test(const char *expr_str, int set_a, int set_b, int set_c, int exp_res)
+{
+ struct tst_expr *expr;
+ int res;
+
+ a = set_a;
+ b = set_b;
+ c = set_c;
+
+ tst_res(TINFO, "'%s' A=%i B=%i C=%i == %i", expr_str, a, b, c, exp_res);
+
+ expr = tst_bool_expr_parse(expr_str);
+
+ if (!expr) {
+ tst_res(TFAIL, "Parser returned error");
+ return;
+ }
+
+ printf("In RPN: ");
+ tst_bool_expr_print(stdout, expr);
+ printf("\n");
+
+ res = tst_bool_expr_eval(expr, map);
+
+ if (res == exp_res)
+ tst_res(TPASS, "Got %i", res);
+ else
+ tst_res(TFAIL, "Got %i", res);
+
+ tst_bool_expr_free(expr);
+}
+
+static void do_test(void)
+{
+ do_eval_test("(A | B) & !!C", 0, 0, 0, 0);
+ do_eval_test("(A | B) & !!C", 1, 0, 1, 1);
+ do_eval_test("!A & B", 1, 0, 0, 0);
+ do_eval_test("!A & B", 0, 1, 0, 1);
+ do_eval_test("A & !B", 1, 0, 0, 1);
+ do_eval_test("!!A & !!B", 0, 1, 0, 0);
+ do_eval_test("!!A & !!B", 1, 1, 0, 1);
+ do_eval_test("!(A & B) & C", 1, 1, 0, 0);
+ do_eval_test("A & (B | C)", 1, 1, 0, 1);
+ do_eval_test("A & B | C", 1, 1, 0, 1);
+ do_eval_test("((((A)))&(B))", 1, 1, 0, 1);
+ do_eval_test(" A \t", 0, 0, 0, 0);
+ do_eval_test("False & A", 1, 0, 0, 0);
+ do_eval_test("! Undefined", 0, 0, 0, -1);
+
+ parse_fail("A!");
+ parse_fail("A &");
+ parse_fail("A B");
+ parse_fail("A ) B");
+ parse_fail("A ( B");
+ parse_fail("A ( B )");
+ parse_fail("A |");
+ parse_fail("A ! B");
+ parse_fail("A! & B");
+ parse_fail("A & | B");
+ parse_fail("A & (B |)");
+ parse_fail("A & ( | B)");
+ parse_fail("A & B &");
+ parse_fail("((A )");
+ parse_fail("& A");
+ parse_fail("! &");
+ parse_fail(")");
+ parse_fail("| A");
+ parse_fail("");
+}
+
+static struct tst_test test = {
+ .test_all = do_test,
+};
diff --git a/lib/tst_bool_expr.c b/lib/tst_bool_expr.c
new file mode 100644
index 000000000..dd147cde3
--- /dev/null
+++ b/lib/tst_bool_expr.c
@@ -0,0 +1,398 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2020 Cyril Hrubis <chrubis@suse.cz>
+ */
+/*
+ * Boolean expression is evaluated in three steps.
+ *
+ * First of all the string containing the expression is tokenized. The
+ * tokenizer runs twice and we only count number of tokens in the first pass in
+ * order to simplify the memory allocation.
+ *
+ * Secondly the the expression is transformed to a postfix (RPN) notation by
+ * the shunting yard algorithm and the correctness of the expression is checked
+ * during the transformation as well. The fact that parenthesis are matched is
+ * asserted by the shunting yard algorithm itself while the rest is checked
+ * simply by checking if the preceding token is in a set of allowed tokens.
+ * This could be thought of as a simple open-coded state machine.
+ *
+ * An expression in the RPN form can be evaluated given a variable mapping
+ * function. The evaluation ignores most of errors because invalid expression
+ * will be rejected in the second step.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include "tst_bool_expr.h"
+
+static int char_to_op(char c)
+{
+ switch (c) {
+ case '(':
+ return TST_OP_LPAR;
+ case ')':
+ return TST_OP_RPAR;
+ case '&':
+ return TST_OP_AND;
+ case '|':
+ return TST_OP_OR;
+ case '!':
+ return TST_OP_NOT;
+ default:
+ return TST_OP_VAR;
+ }
+}
+
+static int new_tok(struct tst_expr_tok **last, const char *tok, size_t tok_len)
+{
+ if (!tok_len)
+ return 0;
+
+ if (!(*last))
+ return 1;
+
+ (*last)->tok = tok;
+ (*last)->tok_len = tok_len;
+ (*last)->op = char_to_op(tok[0]);
+ (*last)++;
+
+ return 1;
+}
+
+static unsigned int tokenize(const char *expr, struct tst_expr_tok *last)
+{
+ size_t i, j;
+ unsigned int token_cnt = 0;
+
+ for (j = i = 0; expr[i]; i++) {
+ switch (expr[i]) {
+ case '(':
+ case ')':
+ case '!':
+ case '&':
+ case '|':
+ token_cnt += new_tok(&last, &expr[j], i - j);
+ token_cnt += new_tok(&last, &expr[i], 1);
+ j = i+1;
+ break;
+ case '\t':
+ case ' ':
+ token_cnt += new_tok(&last, &expr[j], i - j);
+ j = i+1;
+ break;
+ default:
+ break;
+ }
+ }
+
+ token_cnt += new_tok(&last, &expr[j], i - j);
+
+ return token_cnt;
+}
+
+void tst_bool_expr_print(FILE *f, struct tst_expr *expr)
+{
+ struct tst_expr_tok *i;
+ size_t j;
+
+ for (i = expr->rpn; i; i = i->next) {
+ for (j = 0; j < i->tok_len; j++)
+ putc(i->tok[j], f);
+
+ if (i->next)
+ putc(' ', f);
+ }
+}
+
+static void print_spaces(FILE *f, unsigned int spaces)
+{
+ while (spaces--)
+ putc(' ', f);
+}
+
+static void tst_bool_expr_err(FILE *f, struct tst_expr *expr, unsigned int cnt)
+{
+ unsigned int i, spaces, err_len;
+ const char *err;
+
+ fprintf(f, "%s", expr->buf->tok);
+ fprintf(f, "\n");
+
+ for (i = 0; i < cnt; i++) {
+ if (expr->buf[i].priv)
+ break;
+ }
+
+ spaces = expr->buf[i].tok - expr->buf[0].tok;
+ err = expr->buf[i].priv;
+ err_len = strlen(err);
+
+ print_spaces(f, spaces);
+
+ fprintf(f, "^\n");
+
+ if (err_len < spaces)
+ print_spaces(f, spaces - err_len + 1);
+
+ fprintf(f, "%s\n", err);
+}
+
+static inline void stack_push(struct tst_expr_tok *stack[], unsigned int *op_stack_pos,
+ struct tst_expr_tok *op)
+{
+ stack[(*op_stack_pos)++] = op;
+}
+
+static inline int stack_empty(unsigned int op_stack_pos)
+{
+ return op_stack_pos == 0;
+}
+
+static inline struct tst_expr_tok *stack_pop(struct tst_expr_tok *stack[],
+ unsigned int *op_stack_pos)
+{
+ if (stack_empty(*op_stack_pos))
+ return NULL;
+
+ return stack[--(*op_stack_pos)];
+}
+
+#define TST_OP_NONE -1
+
+static inline int stack_peek_op(struct tst_expr_tok *stack[],
+ unsigned int op_stack_pos)
+{
+ if (stack_empty(op_stack_pos))
+ return TST_OP_NONE;
+
+ return stack[op_stack_pos - 1]->op;
+}
+
+/*
+ * This is a complete list of which tokens can happen before any of:
+ * - variable
+ * - left parentesis
+ * - negation
+ *
+ * The -1 represents start of the expression.
+ */
+static inline int check_one(int op)
+{
+ switch (op) {
+ case TST_OP_AND:
+ case TST_OP_OR:
+ case TST_OP_NOT:
+ case TST_OP_NONE:
+ case TST_OP_LPAR:
+ return 0;
+ default:
+ return 1;
+ }
+}
+
+/*
+ * And this checks for tokens that can happen before any of:
+ * - right parentesis
+ * - and
+ * - or
+ *
+ * This is also used to check that the last token in expression is correct one.
+ */
+static inline int check_two(int op)
+{
+ switch (op) {
+ case TST_OP_VAR:
+ case TST_OP_RPAR:
+ return 1;
+ default:
+ return 0;
+ }
+}
+
+static int shunting_yard(struct tst_expr *expr, unsigned int cnt)
+{
+ struct tst_expr_tok *op_stack[cnt];
+ unsigned int op_stack_pos = 0;
+ struct tst_expr_tok *out[cnt + 1];
+ unsigned int out_pos = 0;
+ struct tst_expr_tok *i;
+ unsigned int j;
+ int prev_op = TST_OP_NONE;
+
+ for (i = expr->buf; i < &(expr->buf[cnt]); i++) {
+ switch (i->op) {
+ case TST_OP_VAR:
+ if (check_one(prev_op)) {
+ i->priv = "Expected operation";
+ goto err;
+ }
+
+ stack_push(out, &out_pos, i);
+
+ while (stack_peek_op(op_stack, op_stack_pos) == TST_OP_NOT)
+ stack_push(out, &out_pos, stack_pop(op_stack, &op_stack_pos));
+ break;
+ case TST_OP_LPAR:
+ if (check_one(prev_op)) {
+ i->priv = "Expected operation";
+ goto err;
+ }
+
+ stack_push(op_stack, &op_stack_pos, i);
+ break;
+ case TST_OP_RPAR:
+ if (!check_two(prev_op)) {
+ i->priv = "Expected variable or )";
+ goto err;
+ }
+
+ /* pop everything till ( */
+ for (;;) {
+ struct tst_expr_tok *op = stack_pop(op_stack, &op_stack_pos);
+
+ if (!op) {
+ i->priv = "Missing (";
+ goto err;
+ }
+
+ if (op->op == TST_OP_LPAR)
+ break;
+
+ stack_push(out, &out_pos, op);
+ }
+
+ while (stack_peek_op(op_stack, op_stack_pos) == TST_OP_NOT)
+ stack_push(out, &out_pos, stack_pop(op_stack, &op_stack_pos));
+ break;
+ case TST_OP_NOT:
+ if (check_one(prev_op)) {
+ i->priv = "Expected operation";
+ goto err;
+ }
+ stack_push(op_stack, &op_stack_pos, i);
+ break;
+ case TST_OP_AND:
+ case TST_OP_OR:
+ if (!check_two(prev_op)) {
+ i->priv = "Expected variable or (";
+ goto err;
+ }
+
+ /*
+ * There can be at most one binary op on the stack
+ * since we pop the one present on the stack before we
+ * attempt to push new one they so never accumulate.
+ */
+ switch (stack_peek_op(op_stack, op_stack_pos)) {
+ case TST_OP_AND:
+ case TST_OP_OR:
+ stack_push(out, &out_pos, stack_pop(op_stack, &op_stack_pos));
+ break;
+ }
+
+ stack_push(op_stack, &op_stack_pos, i);
+ break;
+ }
+
+ prev_op = i->op;
+ }
+
+ if (!check_two(expr->buf[cnt-1].op)) {
+ expr->buf[cnt-1].priv = "Unfinished expression";
+ goto err;
+ }
+
+ /* pop remaining operations */
+ while ((i = stack_pop(op_stack, &op_stack_pos))) {
+ if (i->op == TST_OP_LPAR) {
+ i->priv = "Missing )";
+ goto err;
+ }
+
+ stack_push(out, &out_pos, i);
+ }
+
+ /* construct the list */
+ out[out_pos] = NULL;
+
+ for (j = 0; j < out_pos; j++)
+ out[j]->next = out[j + 1];
+
+ expr->rpn = out[0];
+
+ return 0;
+err:
+ return 1;
+}
+
+struct tst_expr *tst_bool_expr_parse(const char *expr)
+{
+ struct tst_expr *ret;
+ unsigned int tok_cnt = tokenize(expr, NULL);
+
+ if (!tok_cnt)
+ return NULL;
+
+ ret = malloc(sizeof(struct tst_expr) + sizeof(struct tst_expr_tok) * tok_cnt);
+ if (!ret)
+ return NULL;
+
+ tokenize(expr, ret->buf);
+
+ if (shunting_yard(ret, tok_cnt)) {
+ tst_bool_expr_err(stderr, ret, tok_cnt);
+ tst_bool_expr_free(ret);
+ return NULL;
+ }
+
+ return ret;
+}
+
+#define MAX_STACK 16
+
+int tst_bool_expr_eval(struct tst_expr *expr,
+ int (*map)(struct tst_expr_tok *var))
+{
+ struct tst_expr_tok *i;
+ int stack[MAX_STACK];
+ int pos = -1;
+
+ for (i = expr->rpn; i; i = i->next) {
+ switch (i->op) {
+ case TST_OP_NOT:
+ stack[pos] = !stack[pos];
+ break;
+ case TST_OP_OR:
+ stack[pos-1] = stack[pos] || stack[pos-1];
+ pos--;
+ break;
+ case TST_OP_AND:
+ stack[pos-1] = stack[pos] && stack[pos-1];
+ pos--;
+ break;
+ case TST_OP_VAR:
+ if (pos + 1 >= MAX_STACK) {
+ fprintf(stderr, "Eval out of stack!\n");
+ return -1;
+ }
+
+ stack[++pos] = map(i);
+
+ /* map reported undefined variable -> abort */
+ if (stack[pos] == -1)
+ return -1;
+ break;
+ /* does not happen */
+ default:
+ break;
+ }
+ }
+
+ return stack[0];
+}
+
+void tst_bool_expr_free(struct tst_expr *expr)
+{
+ free(expr);
+}
--
2.26.2
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