[LTP] [PATCH v3 1/2] lib: Add generic boolean expression parser and eval
Richard Palethorpe
rpalethorpe@suse.de
Tue Nov 3 13:28:23 CET 2020
Hello Metan,
Cyril Hrubis <chrubis@suse.cz> writes:
> 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>
> ---
>
> v3:
> - now we run tokenizer twice and count number of tokens in the first
> pass then allocate all the tokens in one malloc() which simplifies
> the code again a bit
> - sligtly better formatting for error messages
>
> include/tst_bool_expr.h | 86 +++++++
> lib/newlib_tests/.gitignore | 1 +
> lib/newlib_tests/tst_bool_expr.c | 128 ++++++++++
> lib/tst_bool_expr.c | 411 +++++++++++++++++++++++++++++++
> 4 files changed, 626 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..0e2fcc2e7
> --- /dev/null
> +++ b/include/tst_bool_expr.h
> @@ -0,0 +1,86 @@
> +// 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 *expr;
Maybe call this 'first' or 'head'?
> + struct tst_expr_tok *buf;
I suppose that buf could be a trailing array saving a call to malloc and
free :-)
> +};
> +
> +
> +/*
> + * 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..e4cab1474
> --- /dev/null
> +++ b/lib/tst_bool_expr.c
> @@ -0,0 +1,411 @@
> +// 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 *ret)
> +{
> + size_t i, j;
> + unsigned int token_cnt = 0;
> + struct tst_expr_tok *last = ret ? ret->buf : NULL;
> +
> + 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->expr; 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->expr->tok);
> + fprintf(f, "\n");
> +
> + for (i = 0; i < cnt; i++) {
> + if (expr->expr[i].priv)
> + break;
> + }
> +
> + spaces = expr->expr[i].tok - expr->expr[0].tok;
> + err = expr->expr[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;
> + }
> +}
> +
> +/*
> + * Note that we avoid modifying the list until the end so that the caller can
> + * free memory correctly, which is the reason we have a stack for parentesis
> + * that are just freed at the end.
> + */
> +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->expr; i < &(expr->expr[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 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;
> + }
This looks a bit odd as it is the only place you use buf like this. Why
not only use buf until setting expr=out[0] (and only set buf=tok
initially) or only use expr until free(expr->buf) and/or do --i and use
that?
> +
> + /* 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->expr = out[0];
> +
> + return 0;
> +err:
> + return 1;
> +}
> +
> +struct tst_expr *tst_bool_expr_parse(const char *expr)
> +{
> + struct tst_expr *ret;
> + struct tst_expr_tok *tok;
> + unsigned int tok_cnt = tokenize(expr, NULL);
> +
> + if (!tok_cnt)
> + return NULL;
> +
> + ret = malloc(sizeof(struct tst_expr));
> + tok = malloc(sizeof(struct tst_expr_tok) * tok_cnt);
> + if (!ret || !tok) {
> + free(ret);
> + free(tok);
> + return NULL;
> + }
> +
> + ret->expr = ret->buf = tok;
> + tokenize(expr, ret);
> +
> + 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->expr; 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->buf);
> + free(expr);
> +}
> --
> 2.26.2
--
Thank you,
Richard.
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