Imported Upstream version 1.3.0+dfsgupstream/1.3.0+dfsg

1 files changed, 1119 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
new file mode 100644
index 00000000..8866ee95
--- /dev/null
+++ b/src/eval.c
@@ -0,0 +1,1119 @@
+#include "common.h"
+
+// ----------------------------------------------------------------------------
+// data structures for storing the parsed expression in memory
+
+typedef struct eval_value {
+    int type;
+
+    union {
+        calculated_number number;
+        EVAL_VARIABLE *variable;
+        struct eval_node *expression;
+    };
+} EVAL_VALUE;
+
+typedef struct eval_node {
+    int id;
+    unsigned char operator;
+    int precedence;
+
+    int count;
+    EVAL_VALUE ops[];
+} EVAL_NODE;
+
+// these are used for EVAL_NODE.operator
+// they are used as internal IDs to identify an operator
+// THEY ARE NOT USED FOR PARSING OPERATORS LIKE THAT
+#define EVAL_OPERATOR_NOP                   '\0'
+#define EVAL_OPERATOR_EXPRESSION_OPEN       '('
+#define EVAL_OPERATOR_EXPRESSION_CLOSE      ')'
+#define EVAL_OPERATOR_NOT                   '!'
+#define EVAL_OPERATOR_PLUS                  '+'
+#define EVAL_OPERATOR_MINUS                 '-'
+#define EVAL_OPERATOR_AND                   '&'
+#define EVAL_OPERATOR_OR                    '|'
+#define EVAL_OPERATOR_GREATER_THAN_OR_EQUAL 'G'
+#define EVAL_OPERATOR_LESS_THAN_OR_EQUAL    'L'
+#define EVAL_OPERATOR_NOT_EQUAL             '~'
+#define EVAL_OPERATOR_EQUAL                 '='
+#define EVAL_OPERATOR_LESS                  '<'
+#define EVAL_OPERATOR_GREATER               '>'
+#define EVAL_OPERATOR_MULTIPLY              '*'
+#define EVAL_OPERATOR_DIVIDE                '/'
+#define EVAL_OPERATOR_SIGN_PLUS             'P'
+#define EVAL_OPERATOR_SIGN_MINUS            'M'
+#define EVAL_OPERATOR_ABS                   'A'
+#define EVAL_OPERATOR_IF_THEN_ELSE          '?'
+
+// ----------------------------------------------------------------------------
+// forward function definitions
+
+static inline void eval_node_free(EVAL_NODE *op);
+static inline EVAL_NODE *parse_full_expression(const char **string, int *error);
+static inline EVAL_NODE *parse_one_full_operand(const char **string, int *error);
+static inline calculated_number eval_node(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error);
+static inline void print_parsed_as_node(BUFFER *out, EVAL_NODE *op, int *error);
+static inline void print_parsed_as_constant(BUFFER *out, calculated_number n);
+
+// ----------------------------------------------------------------------------
+// evaluation of expressions
+
+static inline calculated_number eval_check_number(calculated_number n, int *error) {
+    if(unlikely(isnan(n))) {
+        *error = EVAL_ERROR_VALUE_IS_NAN;
+        return 0;
+    }
+
+    if(unlikely(isinf(n))) {
+        *error = EVAL_ERROR_VALUE_IS_INFINITE;
+        return 0;
+    }
+
+    return n;
+}
+
+static inline calculated_number eval_variable(EVAL_EXPRESSION *exp, EVAL_VARIABLE *v, int *error) {
+    static uint32_t this_hash = 0, now_hash = 0, after_hash = 0, before_hash = 0;
+    calculated_number n;
+
+    if(unlikely(this_hash == 0)) {
+        this_hash = simple_hash("this");
+        now_hash = simple_hash("now");
+        after_hash = simple_hash("after");
+        before_hash = simple_hash("before");
+    }
+
+    if(v->hash == this_hash && !strcmp(v->name, "this")) {
+        n = (exp->this)?*exp->this:NAN;
+        buffer_strcat(exp->error_msg, "[ $this = ");
+        print_parsed_as_constant(exp->error_msg, n);
+        buffer_strcat(exp->error_msg, " ] ");
+        return n;
+    }
+
+    if(v->hash == after_hash && !strcmp(v->name, "after")) {
+        n = (exp->after && *exp->after)?*exp->after:NAN;
+        buffer_strcat(exp->error_msg, "[ $after = ");
+        print_parsed_as_constant(exp->error_msg, n);
+        buffer_strcat(exp->error_msg, " ] ");
+        return n;
+    }
+
+    if(v->hash == before_hash && !strcmp(v->name, "before")) {
+        n = (exp->before && *exp->before)?*exp->before:NAN;
+        buffer_strcat(exp->error_msg, "[ $before = ");
+        print_parsed_as_constant(exp->error_msg, n);
+        buffer_strcat(exp->error_msg, " ] ");
+        return n;
+    }
+
+    if(v->hash == now_hash && !strcmp(v->name, "now")) {
+        n = time(NULL);
+        buffer_strcat(exp->error_msg, "[ $now = ");
+        print_parsed_as_constant(exp->error_msg, n);
+        buffer_strcat(exp->error_msg, " ] ");
+        return n;
+    }
+
+    if(exp->rrdcalc && health_variable_lookup(v->name, v->hash, exp->rrdcalc, &n)) {
+        buffer_sprintf(exp->error_msg, "[ $%s = ", v->name);
+        print_parsed_as_constant(exp->error_msg, n);
+        buffer_strcat(exp->error_msg, " ] ");
+        return n;
+    }
+
+    *error = EVAL_ERROR_UNKNOWN_VARIABLE;
+    buffer_sprintf(exp->error_msg, "unknown variable '%s'", v->name);
+    return 0;
+}
+
+static inline calculated_number eval_value(EVAL_EXPRESSION *exp, EVAL_VALUE *v, int *error) {
+    calculated_number n;
+
+    switch(v->type) {
+        case EVAL_VALUE_EXPRESSION:
+            n = eval_node(exp, v->expression, error);
+            break;
+
+        case EVAL_VALUE_NUMBER:
+            n = v->number;
+            break;
+
+        case EVAL_VALUE_VARIABLE:
+            n = eval_variable(exp, v->variable, error);
+            break;
+
+        default:
+            *error = EVAL_ERROR_INVALID_VALUE;
+            n = 0;
+            break;
+    }
+
+    // return eval_check_number(n, error);
+    return n;
+}
+
+static inline int is_true(calculated_number n) {
+    if(isnan(n)) return 0;
+    if(isinf(n)) return 1;
+    if(n == 0) return 0;
+    return 1;
+}
+
+calculated_number eval_and(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return is_true(eval_value(exp, &op->ops[0], error)) && is_true(eval_value(exp, &op->ops[1], error));
+}
+calculated_number eval_or(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return is_true(eval_value(exp, &op->ops[0], error)) || is_true(eval_value(exp, &op->ops[1], error));
+}
+calculated_number eval_greater_than_or_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    return isgreaterequal(n1, n2);
+}
+calculated_number eval_less_than_or_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    return islessequal(n1, n2);
+}
+calculated_number eval_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    if(isnan(n1) && isnan(n2)) return 1;
+    if(isinf(n1) && isinf(n2)) return 1;
+    if(isnan(n1) || isnan(n2)) return 0;
+    if(isinf(n1) || isinf(n2)) return 0;
+    return n1 == n2;
+}
+calculated_number eval_not_equal(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return !eval_equal(exp, op, error);
+}
+calculated_number eval_less(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    return isless(n1, n2);
+}
+calculated_number eval_greater(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    return isgreater(n1, n2);
+}
+calculated_number eval_plus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    if(isnan(n1) || isnan(n2)) return NAN;
+    if(isinf(n1) || isinf(n2)) return INFINITY;
+    return n1 + n2;
+}
+calculated_number eval_minus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    if(isnan(n1) || isnan(n2)) return NAN;
+    if(isinf(n1) || isinf(n2)) return INFINITY;
+    return n1 - n2;
+}
+calculated_number eval_multiply(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    if(isnan(n1) || isnan(n2)) return NAN;
+    if(isinf(n1) || isinf(n2)) return INFINITY;
+    return n1 * n2;
+}
+calculated_number eval_divide(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    calculated_number n2 = eval_value(exp, &op->ops[1], error);
+    if(isnan(n1) || isnan(n2)) return NAN;
+    if(isinf(n1) || isinf(n2)) return INFINITY;
+    return n1 / n2;
+}
+calculated_number eval_nop(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return eval_value(exp, &op->ops[0], error);
+}
+calculated_number eval_not(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return !is_true(eval_value(exp, &op->ops[0], error));
+}
+calculated_number eval_sign_plus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    return eval_value(exp, &op->ops[0], error);
+}
+calculated_number eval_sign_minus(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    if(isnan(n1)) return NAN;
+    if(isinf(n1)) return INFINITY;
+    return -n1;
+}
+calculated_number eval_abs(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    calculated_number n1 = eval_value(exp, &op->ops[0], error);
+    if(isnan(n1)) return NAN;
+    if(isinf(n1)) return INFINITY;
+    return abs(n1);
+}
+calculated_number eval_if_then_else(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    if(is_true(eval_value(exp, &op->ops[0], error)))
+        return eval_value(exp, &op->ops[1], error);
+    else
+        return eval_value(exp, &op->ops[2], error);
+}
+
+static struct operator {
+    const char *print_as;
+    char precedence;
+    char parameters;
+    char isfunction;
+    calculated_number (*eval)(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error);
+} operators[256] = {
+        // this is a random access array
+        // we always access it with a known EVAL_OPERATOR_X
+
+        [EVAL_OPERATOR_IF_THEN_ELSE]          = { "?",  1, 3, 0, eval_if_then_else },
+        [EVAL_OPERATOR_AND]                   = { "&&", 2, 2, 0, eval_and },
+        [EVAL_OPERATOR_OR]                    = { "||", 2, 2, 0, eval_or },
+        [EVAL_OPERATOR_GREATER_THAN_OR_EQUAL] = { ">=", 3, 2, 0, eval_greater_than_or_equal },
+        [EVAL_OPERATOR_LESS_THAN_OR_EQUAL]    = { "<=", 3, 2, 0, eval_less_than_or_equal },
+        [EVAL_OPERATOR_NOT_EQUAL]             = { "!=", 3, 2, 0, eval_not_equal },
+        [EVAL_OPERATOR_EQUAL]                 = { "==", 3, 2, 0, eval_equal },
+        [EVAL_OPERATOR_LESS]                  = { "<",  3, 2, 0, eval_less },
+        [EVAL_OPERATOR_GREATER]               = { ">",  3, 2, 0, eval_greater },
+        [EVAL_OPERATOR_PLUS]                  = { "+",  4, 2, 0, eval_plus },
+        [EVAL_OPERATOR_MINUS]                 = { "-",  4, 2, 0, eval_minus },
+        [EVAL_OPERATOR_MULTIPLY]              = { "*",  5, 2, 0, eval_multiply },
+        [EVAL_OPERATOR_DIVIDE]                = { "/",  5, 2, 0, eval_divide },
+        [EVAL_OPERATOR_NOT]                   = { "!",  6, 1, 0, eval_not },
+        [EVAL_OPERATOR_SIGN_PLUS]             = { "+",  6, 1, 0, eval_sign_plus },
+        [EVAL_OPERATOR_SIGN_MINUS]            = { "-",  6, 1, 0, eval_sign_minus },
+        [EVAL_OPERATOR_ABS]                   = { "abs(",6,1, 1, eval_abs },
+        [EVAL_OPERATOR_NOP]                   = { NULL, 7, 1, 0, eval_nop },
+        [EVAL_OPERATOR_EXPRESSION_OPEN]       = { NULL, 7, 1, 0, eval_nop },
+
+        // this should exist in our evaluation list
+        [EVAL_OPERATOR_EXPRESSION_CLOSE]      = { NULL, 99, 1, 0, eval_nop }
+};
+
+#define eval_precedence(operator) (operators[(unsigned char)(operator)].precedence)
+
+static inline calculated_number eval_node(EVAL_EXPRESSION *exp, EVAL_NODE *op, int *error) {
+    if(unlikely(op->count != operators[op->operator].parameters)) {
+        *error = EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS;
+        return 0;
+    }
+
+    calculated_number n = operators[op->operator].eval(exp, op, error);
+
+    // return eval_check_number(n, error);
+    return n;
+}
+
+// ----------------------------------------------------------------------------
+// parsed-as generation
+
+static inline void print_parsed_as_variable(BUFFER *out, EVAL_VARIABLE *v, int *error) {
+    (void)error;
+    buffer_sprintf(out, "$%s", v->name);
+}
+
+static inline void print_parsed_as_constant(BUFFER *out, calculated_number n) {
+    if(unlikely(isnan(n))) {
+        buffer_strcat(out, "nan");
+        return;
+    }
+
+    if(unlikely(isinf(n))) {
+        buffer_strcat(out, "inf");
+        return;
+    }
+
+    char b[100+1], *s;
+    snprintfz(b, 100, CALCULATED_NUMBER_FORMAT, n);
+
+    s = &b[strlen(b) - 1];
+    while(s > b && *s == '0') {
+        *s ='\0';
+        s--;
+    }
+
+    if(s > b && *s == '.')
+        *s = '\0';
+
+    buffer_strcat(out, b);
+}
+
+static inline void print_parsed_as_value(BUFFER *out, EVAL_VALUE *v, int *error) {
+    switch(v->type) {
+        case EVAL_VALUE_EXPRESSION:
+            print_parsed_as_node(out, v->expression, error);
+            break;
+
+        case EVAL_VALUE_NUMBER:
+            print_parsed_as_constant(out, v->number);
+            break;
+
+        case EVAL_VALUE_VARIABLE:
+            print_parsed_as_variable(out, v->variable, error);
+            break;
+
+        default:
+            *error = EVAL_ERROR_INVALID_VALUE;
+            break;
+    }
+}
+
+static inline void print_parsed_as_node(BUFFER *out, EVAL_NODE *op, int *error) {
+    if(unlikely(op->count != operators[op->operator].parameters)) {
+        *error = EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS;
+        return;
+    }
+
+    if(operators[op->operator].parameters == 1) {
+
+        if(operators[op->operator].print_as)
+            buffer_sprintf(out, "%s", operators[op->operator].print_as);
+
+        //if(op->operator == EVAL_OPERATOR_EXPRESSION_OPEN)
+        //    buffer_strcat(out, "(");
+
+        print_parsed_as_value(out, &op->ops[0], error);
+
+        //if(op->operator == EVAL_OPERATOR_EXPRESSION_OPEN)
+        //    buffer_strcat(out, ")");
+    }
+
+    else if(operators[op->operator].parameters == 2) {
+        buffer_strcat(out, "(");
+        print_parsed_as_value(out, &op->ops[0], error);
+
+        if(operators[op->operator].print_as)
+            buffer_sprintf(out, " %s ", operators[op->operator].print_as);
+
+        print_parsed_as_value(out, &op->ops[1], error);
+        buffer_strcat(out, ")");
+    }
+    else if(op->operator == EVAL_OPERATOR_IF_THEN_ELSE && operators[op->operator].parameters == 3) {
+        buffer_strcat(out, "(");
+        print_parsed_as_value(out, &op->ops[0], error);
+
+        if(operators[op->operator].print_as)
+            buffer_sprintf(out, " %s ", operators[op->operator].print_as);
+
+        print_parsed_as_value(out, &op->ops[1], error);
+        buffer_strcat(out, " : ");
+        print_parsed_as_value(out, &op->ops[2], error);
+        buffer_strcat(out, ")");
+    }
+
+    if(operators[op->operator].isfunction)
+        buffer_strcat(out, ")");
+}
+
+// ----------------------------------------------------------------------------
+// parsing expressions
+
+// skip spaces
+static inline void skip_spaces(const char **string) {
+    const char *s = *string;
+    while(isspace(*s)) s++;
+    *string = s;
+}
+
+// what character can appear just after an operator keyword
+// like NOT AND OR ?
+static inline int isoperatorterm_word(const char s) {
+    if(isspace(s) || s == '(' || s == '$' || s == '!' || s == '-' || s == '+' || isdigit(s) || !s)
+        return 1;
+
+    return 0;
+}
+
+// what character can appear just after an operator symbol?
+static inline int isoperatorterm_symbol(const char s) {
+    if(isoperatorterm_word(s) || isalpha(s))
+        return 1;
+
+    return 0;
+}
+
+// return 1 if the character should never appear in a variable
+static inline int isvariableterm(const char s) {
+    if(isalnum(s) || s == '.' || s == '_')
+        return 0;
+
+    return 1;
+}
+
+// ----------------------------------------------------------------------------
+// parse operators
+
+static inline int parse_and(const char **string) {
+    const char *s = *string;
+
+    // AND
+    if((s[0] == 'A' || s[0] == 'a') && (s[1] == 'N' || s[1] == 'n') && (s[2] == 'D' || s[2] == 'd') && isoperatorterm_word(s[3])) {
+        *string = &s[4];
+        return 1;
+    }
+
+    // &&
+    if(s[0] == '&' && s[1] == '&' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_or(const char **string) {
+    const char *s = *string;
+
+    // OR
+    if((s[0] == 'O' || s[0] == 'o') && (s[1] == 'R' || s[1] == 'r') && isoperatorterm_word(s[2])) {
+        *string = &s[3];
+        return 1;
+    }
+
+    // ||
+    if(s[0] == '|' && s[1] == '|' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_greater_than_or_equal(const char **string) {
+    const char *s = *string;
+
+    // >=
+    if(s[0] == '>' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_less_than_or_equal(const char **string) {
+    const char *s = *string;
+
+    // <=
+    if (s[0] == '<' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_greater(const char **string) {
+    const char *s = *string;
+
+    // >
+    if(s[0] == '>' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_less(const char **string) {
+    const char *s = *string;
+
+    // <
+    if(s[0] == '<' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_equal(const char **string) {
+    const char *s = *string;
+
+    // ==
+    if(s[0] == '=' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    // =
+    if(s[0] == '=' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_not_equal(const char **string) {
+    const char *s = *string;
+
+    // !=
+    if(s[0] == '!' && s[1] == '=' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+        return 1;
+    }
+
+    // <>
+    if(s[0] == '<' && s[1] == '>' && isoperatorterm_symbol(s[2])) {
+        *string = &s[2];
+    }
+
+    return 0;
+}
+
+static inline int parse_not(const char **string) {
+    const char *s = *string;
+
+    // NOT
+    if((s[0] == 'N' || s[0] == 'n') && (s[1] == 'O' || s[1] == 'o') && (s[2] == 'T' || s[2] == 't') && isoperatorterm_word(s[3])) {
+        *string = &s[3];
+        return 1;
+    }
+
+    if(s[0] == '!') {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_multiply(const char **string) {
+    const char *s = *string;
+
+    // *
+    if(s[0] == '*' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_divide(const char **string) {
+    const char *s = *string;
+
+    // /
+    if(s[0] == '/' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_minus(const char **string) {
+    const char *s = *string;
+
+    // -
+    if(s[0] == '-' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_plus(const char **string) {
+    const char *s = *string;
+
+    // +
+    if(s[0] == '+' && isoperatorterm_symbol(s[1])) {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_open_subexpression(const char **string) {
+    const char *s = *string;
+
+    // (
+    if(s[0] == '(') {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+#define parse_close_function(x) parse_close_subexpression(x)
+
+static inline int parse_close_subexpression(const char **string) {
+    const char *s = *string;
+
+    // )
+    if(s[0] == ')') {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_variable(const char **string, char *buffer, size_t len) {
+    const char *s = *string;
+
+    // $
+    if(s[0] == '$') {
+        size_t i = 0;
+        s++;
+
+        while(*s && !isvariableterm(*s) && i < len)
+            buffer[i++] = *s++;
+
+        buffer[i] = '\0';
+
+        if(buffer[0]) {
+            *string = &s[0];
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+static inline int parse_constant(const char **string, calculated_number *number) {
+    char *end = NULL;
+    calculated_number n = strtold(*string, &end);
+    if(unlikely(!end || *string == end)) {
+        *number = 0;
+        return 0;
+    }
+    *number = n;
+    *string = end;
+    return 1;
+}
+
+static inline int parse_abs(const char **string) {
+    const char *s = *string;
+
+    // ABS
+    if((s[0] == 'A' || s[0] == 'a') && (s[1] == 'B' || s[1] == 'b') && (s[2] == 'S' || s[2] == 's') && s[3] == '(') {
+        *string = &s[3];
+        return 1;
+    }
+
+    return 0;
+}
+
+static inline int parse_if_then_else(const char **string) {
+    const char *s = *string;
+
+    // ?
+    if(s[0] == '?') {
+        *string = &s[1];
+        return 1;
+    }
+
+    return 0;
+}
+
+static struct operator_parser {
+    unsigned char id;
+    int (*parse)(const char **);
+} operator_parsers[] = {
+        // the order in this list is important!
+        // the first matching will be used
+        // so place the longer of overlapping ones
+        // at the top
+
+        { EVAL_OPERATOR_AND,                   parse_and },
+        { EVAL_OPERATOR_OR,                    parse_or },
+        { EVAL_OPERATOR_GREATER_THAN_OR_EQUAL, parse_greater_than_or_equal },
+        { EVAL_OPERATOR_LESS_THAN_OR_EQUAL,    parse_less_than_or_equal },
+        { EVAL_OPERATOR_NOT_EQUAL,             parse_not_equal },
+        { EVAL_OPERATOR_EQUAL,                 parse_equal },
+        { EVAL_OPERATOR_LESS,                  parse_less },
+        { EVAL_OPERATOR_GREATER,               parse_greater },
+        { EVAL_OPERATOR_PLUS,                  parse_plus },
+        { EVAL_OPERATOR_MINUS,                 parse_minus },
+        { EVAL_OPERATOR_MULTIPLY,              parse_multiply },
+        { EVAL_OPERATOR_DIVIDE,                parse_divide },
+        { EVAL_OPERATOR_IF_THEN_ELSE,          parse_if_then_else },
+
+        /* we should not put in this list the following:
+         *
+         *  - NOT
+         *  - (
+         *  - )
+         *
+         * these are handled in code
+         */
+
+        // termination
+        { EVAL_OPERATOR_NOP, NULL }
+};
+
+static inline unsigned char parse_operator(const char **string, int *precedence) {
+    skip_spaces(string);
+
+    int i;
+    for(i = 0 ; operator_parsers[i].parse != NULL ; i++)
+        if(operator_parsers[i].parse(string)) {
+            if(precedence) *precedence = eval_precedence(operator_parsers[i].id);
+            return operator_parsers[i].id;
+        }
+
+    return EVAL_OPERATOR_NOP;
+}
+
+// ----------------------------------------------------------------------------
+// memory management
+
+static inline EVAL_NODE *eval_node_alloc(int count) {
+    static int id = 1;
+
+    EVAL_NODE *op = callocz(1, sizeof(EVAL_NODE) + (sizeof(EVAL_VALUE) * count));
+
+    op->id = id++;
+    op->operator = EVAL_OPERATOR_NOP;
+    op->precedence = eval_precedence(EVAL_OPERATOR_NOP);
+    op->count = count;
+    return op;
+}
+
+static inline void eval_node_set_value_to_node(EVAL_NODE *op, int pos, EVAL_NODE *value) {
+    if(pos >= op->count)
+        fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+    op->ops[pos].type = EVAL_VALUE_EXPRESSION;
+    op->ops[pos].expression = value;
+}
+
+static inline void eval_node_set_value_to_constant(EVAL_NODE *op, int pos, calculated_number value) {
+    if(pos >= op->count)
+        fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+    op->ops[pos].type = EVAL_VALUE_NUMBER;
+    op->ops[pos].number = value;
+}
+
+static inline void eval_node_set_value_to_variable(EVAL_NODE *op, int pos, const char *variable) {
+    if(pos >= op->count)
+        fatal("Invalid request to set position %d of OPERAND that has only %d values", pos + 1, op->count + 1);
+
+    op->ops[pos].type = EVAL_VALUE_VARIABLE;
+    op->ops[pos].variable = callocz(1, sizeof(EVAL_VARIABLE));
+    op->ops[pos].variable->name = strdupz(variable);
+    op->ops[pos].variable->hash = simple_hash(op->ops[pos].variable->name);
+}
+
+static inline void eval_variable_free(EVAL_VARIABLE *v) {
+    freez(v->name);
+    freez(v);
+}
+
+static inline void eval_value_free(EVAL_VALUE *v) {
+    switch(v->type) {
+        case EVAL_VALUE_EXPRESSION:
+            eval_node_free(v->expression);
+            break;
+
+        case EVAL_VALUE_VARIABLE:
+            eval_variable_free(v->variable);
+            break;
+
+        default:
+            break;
+    }
+}
+
+static inline void eval_node_free(EVAL_NODE *op) {
+    if(op->count) {
+        int i;
+        for(i = op->count - 1; i >= 0 ;i--)
+            eval_value_free(&op->ops[i]);
+    }
+
+    freez(op);
+}
+
+// ----------------------------------------------------------------------------
+// the parsing logic
+
+// helper function to avoid allocations all over the place
+static inline EVAL_NODE *parse_next_operand_given_its_operator(const char **string, unsigned char operator_type, int *error) {
+    EVAL_NODE *sub = parse_one_full_operand(string, error);
+    if(!sub) return NULL;
+
+    EVAL_NODE *op = eval_node_alloc(1);
+    op->operator = operator_type;
+    eval_node_set_value_to_node(op, 0, sub);
+    return op;
+}
+
+// parse a full operand, including its sign or other associative operator (e.g. NOT)
+static inline EVAL_NODE *parse_one_full_operand(const char **string, int *error) {
+    char variable_buffer[EVAL_MAX_VARIABLE_NAME_LENGTH + 1];
+    EVAL_NODE *op1 = NULL;
+    calculated_number number;
+
+    *error = EVAL_ERROR_OK;
+
+    skip_spaces(string);
+    if(!(**string)) {
+        *error = EVAL_ERROR_MISSING_OPERAND;
+        return NULL;
+    }
+
+    if(parse_not(string)) {
+        op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_NOT, error);
+        op1->precedence = eval_precedence(EVAL_OPERATOR_NOT);
+    }
+    else if(parse_plus(string)) {
+        op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_SIGN_PLUS, error);
+        op1->precedence = eval_precedence(EVAL_OPERATOR_SIGN_PLUS);
+    }
+    else if(parse_minus(string)) {
+        op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_SIGN_MINUS, error);
+        op1->precedence = eval_precedence(EVAL_OPERATOR_SIGN_MINUS);
+    }
+    else if(parse_abs(string)) {
+        op1 = parse_next_operand_given_its_operator(string, EVAL_OPERATOR_ABS, error);
+        op1->precedence = eval_precedence(EVAL_OPERATOR_ABS);
+    }
+    else if(parse_open_subexpression(string)) {
+        EVAL_NODE *sub = parse_full_expression(string, error);
+        if(sub) {
+            op1 = eval_node_alloc(1);
+            op1->operator = EVAL_OPERATOR_EXPRESSION_OPEN;
+            op1->precedence = eval_precedence(EVAL_OPERATOR_EXPRESSION_OPEN);
+            eval_node_set_value_to_node(op1, 0, sub);
+            if(!parse_close_subexpression(string)) {
+                *error = EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION;
+                eval_node_free(op1);
+                return NULL;
+            }
+        }
+    }
+    else if(parse_variable(string, variable_buffer, EVAL_MAX_VARIABLE_NAME_LENGTH)) {
+        op1 = eval_node_alloc(1);
+        op1->operator = EVAL_OPERATOR_NOP;
+        eval_node_set_value_to_variable(op1, 0, variable_buffer);
+    }
+    else if(parse_constant(string, &number)) {
+        op1 = eval_node_alloc(1);
+        op1->operator = EVAL_OPERATOR_NOP;
+        eval_node_set_value_to_constant(op1, 0, number);
+    }
+    else if(**string)
+        *error = EVAL_ERROR_UNKNOWN_OPERAND;
+    else
+        *error = EVAL_ERROR_MISSING_OPERAND;
+
+    return op1;
+}
+
+// parse an operator and the rest of the expression
+// precedence processing is handled here
+static inline EVAL_NODE *parse_rest_of_expression(const char **string, int *error, EVAL_NODE *op1) {
+    EVAL_NODE *op2 = NULL;
+    unsigned char operator;
+    int precedence;
+
+    operator = parse_operator(string, &precedence);
+    skip_spaces(string);
+
+    if(operator != EVAL_OPERATOR_NOP) {
+        op2 = parse_one_full_operand(string, error);
+        if(!op2) {
+            // error is already reported
+            eval_node_free(op1);
+            return NULL;
+        }
+
+        EVAL_NODE *op = eval_node_alloc(operators[operator].parameters);
+        op->operator = operator;
+        op->precedence = precedence;
+
+        if(operator == EVAL_OPERATOR_IF_THEN_ELSE && op->count == 3) {
+            skip_spaces(string);
+
+            if(**string != ':') {
+                eval_node_free(op);
+                eval_node_free(op1);
+                eval_node_free(op2);
+                *error = EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE;
+                return NULL;
+            }
+            (*string)++;
+
+            skip_spaces(string);
+
+            EVAL_NODE *op3 = parse_one_full_operand(string, error);
+            if(!op3) {
+                eval_node_free(op);
+                eval_node_free(op1);
+                eval_node_free(op2);
+                // error is already reported
+                return NULL;
+            }
+
+            eval_node_set_value_to_node(op, 2, op3);
+        }
+
+        eval_node_set_value_to_node(op, 1, op2);
+
+        // precedence processing
+        // if this operator has a higher precedence compared to its next
+        // put the next operator on top of us (top = evaluated later)
+        // function recursion does the rest...
+        if(op->precedence > op1->precedence && op1->count == 2 && op1->operator != '(' && op1->ops[1].type == EVAL_VALUE_EXPRESSION) {
+            eval_node_set_value_to_node(op, 0, op1->ops[1].expression);
+            op1->ops[1].expression = op;
+            op = op1;
+        }
+        else
+            eval_node_set_value_to_node(op, 0, op1);
+
+        return parse_rest_of_expression(string, error, op);
+    }
+    else if(**string == ')') {
+        ;
+    }
+    else if(**string) {
+        eval_node_free(op1);
+        op1 = NULL;
+        *error = EVAL_ERROR_MISSING_OPERATOR;
+    }
+
+    return op1;
+}
+
+// high level function to parse an expression or a sub-expression
+static inline EVAL_NODE *parse_full_expression(const char **string, int *error) {
+    EVAL_NODE *op1 = NULL;
+
+    op1 = parse_one_full_operand(string, error);
+    if(!op1) {
+        *error = EVAL_ERROR_MISSING_OPERAND;
+        return NULL;
+    }
+
+    return parse_rest_of_expression(string, error, op1);
+}
+
+// ----------------------------------------------------------------------------
+// public API
+
+int expression_evaluate(EVAL_EXPRESSION *exp) {
+    exp->error = EVAL_ERROR_OK;
+
+    buffer_reset(exp->error_msg);
+    exp->result = eval_node(exp, (EVAL_NODE *)exp->nodes, &exp->error);
+
+    if(exp->error == EVAL_ERROR_OK)
+        exp->result = eval_check_number(exp->result, &exp->error);
+
+    if(exp->error != EVAL_ERROR_OK) {
+        exp->result = NAN;
+
+        if(buffer_strlen(exp->error_msg))
+            buffer_strcat(exp->error_msg, "; ");
+
+        buffer_sprintf(exp->error_msg, "failed to evaluate expression with error %d (%s)", exp->error, expression_strerror(exp->error));
+        return 0;
+    }
+
+    return 1;
+}
+
+EVAL_EXPRESSION *expression_parse(const char *string, const char **failed_at, int *error) {
+    const char *s = string;
+    int err = EVAL_ERROR_OK;
+    unsigned long pos = 0;
+
+    EVAL_NODE *op = parse_full_expression(&s, &err);
+
+    if(*s) {
+        if(op) {
+            eval_node_free(op);
+            op = NULL;
+        }
+        err = EVAL_ERROR_REMAINING_GARBAGE;
+    }
+
+    if (failed_at) *failed_at = s;
+    if (error) *error = err;
+
+    if(!op) {
+        pos = s - string + 1;
+        error("failed to parse expression '%s': %s at character %lu (i.e.: '%s').", string, expression_strerror(err), pos, s);
+        return NULL;
+    }
+
+    BUFFER *out = buffer_create(1024);
+    print_parsed_as_node(out, op, &err);
+    if(err != EVAL_ERROR_OK) {
+        error("failed to re-generate expression '%s' with reason: %s", string, expression_strerror(err));
+        eval_node_free(op);
+        buffer_free(out);
+        return NULL;
+    }
+
+    EVAL_EXPRESSION *exp = callocz(1, sizeof(EVAL_EXPRESSION));
+
+    exp->source = strdupz(string);
+    exp->parsed_as = strdupz(buffer_tostring(out));
+    buffer_free(out);
+
+    exp->error_msg = buffer_create(100);
+    exp->nodes = (void *)op;
+
+    return exp;
+}
+
+void expression_free(EVAL_EXPRESSION *exp) {
+    if(!exp) return;
+
+    if(exp->nodes) eval_node_free((EVAL_NODE *)exp->nodes);
+    freez((void *)exp->source);
+    freez((void *)exp->parsed_as);
+    buffer_free(exp->error_msg);
+    freez(exp);
+}
+
+const char *expression_strerror(int error) {
+    switch(error) {
+        case EVAL_ERROR_OK:
+            return "success";
+
+        case EVAL_ERROR_MISSING_CLOSE_SUBEXPRESSION:
+            return "missing closing parenthesis";
+
+        case EVAL_ERROR_UNKNOWN_OPERAND:
+            return "unknown operand";
+
+        case EVAL_ERROR_MISSING_OPERAND:
+            return "expected operand";
+
+        case EVAL_ERROR_MISSING_OPERATOR:
+            return "expected operator";
+
+        case EVAL_ERROR_REMAINING_GARBAGE:
+            return "remaining characters after expression";
+
+        case EVAL_ERROR_INVALID_VALUE:
+            return "invalid value structure - internal error";
+
+        case EVAL_ERROR_INVALID_NUMBER_OF_OPERANDS:
+            return "wrong number of operands for operation - internal error";
+
+        case EVAL_ERROR_VALUE_IS_NAN:
+            return "value is unset";
+
+        case EVAL_ERROR_VALUE_IS_INFINITE:
+            return "computed value is infinite";
+
+        case EVAL_ERROR_UNKNOWN_VARIABLE:
+            return "undefined variable";
+
+        case EVAL_ERROR_IF_THEN_ELSE_MISSING_ELSE:
+            return "missing second sub-expression of inline conditional";
+
+        default:
+            return "unknown error";
+    }
+}