/*
 * Arithmetic code ripped out of ash shell for code sharing.
 *
 * This code is derived from software contributed to Berkeley by
 * Kenneth Almquist.
 *
 * Original BSD copyright notice is retained at the end of this file.
 *
 * Copyright (c) 1989, 1991, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * Copyright (c) 1997-2005 Herbert Xu <herbert@gondor.apana.org.au>
 * was re-ported from NetBSD and debianized.
 *
 * rewrite arith.y to micro stack based cryptic algorithm by
 * Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
 *
 * Modified by Paul Mundt <lethal@linux-sh.org> (c) 2004 to support
 * dynamic variables.
 *
 * Modified by Vladimir Oleynik <dzo@simtreas.ru> (c) 2001-2005 to be
 * used in busybox and size optimizations,
 * rewrote arith (see notes to this), added locale support,
 * rewrote dynamic variables.
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
/* Copyright (c) 2001 Aaron Lehmann <aaronl@vitelus.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/* This is my infix parser/evaluator. It is optimized for size, intended
 * as a replacement for yacc-based parsers. However, it may well be faster
 * than a comparable parser written in yacc. The supported operators are
 * listed in #defines below. Parens, order of operations, and error handling
 * are supported. This code is thread safe. The exact expression format should
 * be that which POSIX specifies for shells.
 *
 * The code uses a simple two-stack algorithm. See
 * http://www.onthenet.com.au/~grahamis/int2008/week02/lect02.html
 * for a detailed explanation of the infix-to-postfix algorithm on which
 * this is based (this code differs in that it applies operators immediately
 * to the stack instead of adding them to a queue to end up with an
 * expression).
 */

/*
 * Aug 24, 2001              Manuel Novoa III
 *
 * Reduced the generated code size by about 30% (i386) and fixed several bugs.
 *
 * 1) In arith_apply():
 *    a) Cached values of *numptr and &(numptr[-1]).
 *    b) Removed redundant test for zero denominator.
 *
 * 2) In arith():
 *    a) Eliminated redundant code for processing operator tokens by moving
 *       to a table-based implementation.  Also folded handling of parens
 *       into the table.
 *    b) Combined all 3 loops which called arith_apply to reduce generated
 *       code size at the cost of speed.
 *
 * 3) The following expressions were treated as valid by the original code:
 *       1()  ,    0!  ,    1 ( *3 )   .
 *    These bugs have been fixed by internally enclosing the expression in
 *    parens and then checking that all binary ops and right parens are
 *    preceded by a valid expression (NUM_TOKEN).
 *
 * Note: It may be desirable to replace Aaron's test for whitespace with
 * ctype's isspace() if it is used by another busybox applet or if additional
 * whitespace chars should be considered.  Look below the "#include"s for a
 * precompiler test.
 */
/*
 * Aug 26, 2001              Manuel Novoa III
 *
 * Return 0 for null expressions.  Pointed out by Vladimir Oleynik.
 *
 * Merge in Aaron's comments previously posted to the busybox list,
 * modified slightly to take account of my changes to the code.
 *
 */
/*
 *  (C) 2003 Vladimir Oleynik <dzo@simtreas.ru>
 *
 * - allow access to variable,
 *   use recursive value indirection: c="2*2"; a="c"; echo $((a+=2)) produce 6
 * - implement assign syntax (VAR=expr, +=, *= etc)
 * - implement exponentiation (** operator)
 * - implement comma separated - expr, expr
 * - implement ++expr --expr expr++ expr--
 * - implement expr ? expr : expr (but second expr is always calculated)
 * - allow hexadecimal and octal numbers
 * - restore lost XOR operator
 * - protect $((num num)) as true zero expr (Manuel's error)
 * - always use special isspace(), see comment from bash ;-)
 */
#include "libbb.h"
#include "math.h"

#define lookupvar (math_state->lookupvar)
#define setvar    (math_state->setvar   )
//#define endofname (math_state->endofname)

typedef unsigned char operator;

/* An operator's token id is a bit of a bitfield. The lower 5 bits are the
 * precedence, and 3 high bits are an ID unique across operators of that
 * precedence. The ID portion is so that multiple operators can have the
 * same precedence, ensuring that the leftmost one is evaluated first.
 * Consider * and /
 */
#define tok_decl(prec,id)       (((id)<<5) | (prec))
#define PREC(op)                ((op) & 0x1F)

#define TOK_LPAREN              tok_decl(0,0)

#define TOK_COMMA               tok_decl(1,0)

/* All assignments are right associative and have the same precedence,
 * but there are 11 of them, which doesn't fit into 3 bits for unique id.
 * Abusing another precedence level:
 */
#define TOK_ASSIGN              tok_decl(2,0)
#define TOK_AND_ASSIGN          tok_decl(2,1)
#define TOK_OR_ASSIGN           tok_decl(2,2)
#define TOK_XOR_ASSIGN          tok_decl(2,3)
#define TOK_PLUS_ASSIGN         tok_decl(2,4)
#define TOK_MINUS_ASSIGN        tok_decl(2,5)
#define TOK_LSHIFT_ASSIGN       tok_decl(2,6)
#define TOK_RSHIFT_ASSIGN       tok_decl(2,7)

#define TOK_MUL_ASSIGN          tok_decl(3,0)
#define TOK_DIV_ASSIGN          tok_decl(3,1)
#define TOK_REM_ASSIGN          tok_decl(3,2)

#define fix_assignment_prec(prec) do { if (prec == 3) prec = 2; } while (0)

/* Ternary conditional operator is right associative too */
#define TOK_CONDITIONAL         tok_decl(4,0)
#define TOK_CONDITIONAL_SEP     tok_decl(4,1)

#define TOK_OR                  tok_decl(5,0)

#define TOK_AND                 tok_decl(6,0)

#define TOK_BOR                 tok_decl(7,0)

#define TOK_BXOR                tok_decl(8,0)

#define TOK_BAND                tok_decl(9,0)

#define TOK_EQ                  tok_decl(10,0)
#define TOK_NE                  tok_decl(10,1)

#define TOK_LT                  tok_decl(11,0)
#define TOK_GT                  tok_decl(11,1)
#define TOK_GE                  tok_decl(11,2)
#define TOK_LE                  tok_decl(11,3)

#define TOK_LSHIFT              tok_decl(12,0)
#define TOK_RSHIFT              tok_decl(12,1)

#define TOK_ADD                 tok_decl(13,0)
#define TOK_SUB                 tok_decl(13,1)

#define TOK_MUL                 tok_decl(14,0)
#define TOK_DIV                 tok_decl(14,1)
#define TOK_REM                 tok_decl(14,2)

/* Exponent is right associative */
#define TOK_EXPONENT            tok_decl(15,1)

/* Unary operators */
#define UNARYPREC               16
#define TOK_BNOT                tok_decl(UNARYPREC,0)
#define TOK_NOT                 tok_decl(UNARYPREC,1)

#define TOK_UMINUS              tok_decl(UNARYPREC+1,0)
#define TOK_UPLUS               tok_decl(UNARYPREC+1,1)

#define PREC_PRE                (UNARYPREC+2)

#define TOK_PRE_INC             tok_decl(PREC_PRE, 0)
#define TOK_PRE_DEC             tok_decl(PREC_PRE, 1)

#define PREC_POST               (UNARYPREC+3)

#define TOK_POST_INC            tok_decl(PREC_POST, 0)
#define TOK_POST_DEC            tok_decl(PREC_POST, 1)

#define SPEC_PREC               (UNARYPREC+4)

#define TOK_NUM                 tok_decl(SPEC_PREC, 0)
#define TOK_RPAREN              tok_decl(SPEC_PREC, 1)

static int
is_assign_op(operator op)
{
        operator prec = PREC(op);
        fix_assignment_prec(prec);
        return prec == PREC(TOK_ASSIGN)
        || prec == PREC_PRE
        || prec == PREC_POST;
}

static int
is_right_associative(operator prec)
{
        return prec == PREC(TOK_ASSIGN)
        || prec == PREC(TOK_EXPONENT)
        || prec == PREC(TOK_CONDITIONAL);
}


typedef struct {
        arith_t val;
        /* We acquire second_val only when "expr1 : expr2" part
         * of ternary ?: op is evaluated.
         * We treat ?: as two binary ops: (expr ? (expr1 : expr2)).
         * ':' produces a new value which has two parts, val and second_val;
         * then '?' selects one of them based on its left side.
         */
        arith_t second_val;
        char second_val_present;
        /* If NULL then it's just a number, else it's a named variable */
        char *var;
} var_or_num_t;

typedef struct remembered_name {
        struct remembered_name *next;
        const char *var;
} remembered_name;


static arith_t FAST_FUNC
evaluate_string(arith_state_t *math_state, const char *expr);

static const char*
arith_lookup_val(arith_state_t *math_state, var_or_num_t *t)
{
        if (t->var) {
                const char *p = lookupvar(t->var);
                if (p) {
                        remembered_name *cur;
                        remembered_name cur_save;

                        /* did we already see this name?
                         * testcase: a=b; b=a; echo $((a))
                         */
                        for (cur = math_state->list_of_recursed_names; cur; cur = cur->next) {
                                if (strcmp(cur->var, t->var) == 0) {
                                        /* Yes */
                                        return "expression recursion loop detected";
                                }
                        }

                        /* push current var name */
                        cur = math_state->list_of_recursed_names;
                        cur_save.var = t->var;
                        cur_save.next = cur;
                        math_state->list_of_recursed_names = &cur_save;

                        /* recursively evaluate p as expression */
                        t->val = evaluate_string(math_state, p);

                        /* pop current var name */
                        math_state->list_of_recursed_names = cur;

                        return math_state->errmsg;
                }
                /* treat undefined var as 0 */
                t->val = 0;
        }
        return 0;
}

/* "Applying" a token means performing it on the top elements on the integer
 * stack. For an unary operator it will only change the top element, but a
 * binary operator will pop two arguments and push the result */
static NOINLINE const char*
arith_apply(arith_state_t *math_state, operator op, var_or_num_t *numstack, var_or_num_t **numstackptr)
{
#define NUMPTR (*numstackptr)

        var_or_num_t *top_of_stack;
        arith_t rez;
        const char *err;

        /* There is no operator that can work without arguments */
        if (NUMPTR == numstack)
                goto err;

        top_of_stack = NUMPTR - 1;

        /* Resolve name to value, if needed */
        err = arith_lookup_val(math_state, top_of_stack);
        if (err)
                return err;

        rez = top_of_stack->val;
        if (op == TOK_UMINUS)
                rez = -rez;
        else if (op == TOK_NOT)
                rez = !rez;
        else if (op == TOK_BNOT)
                rez = ~rez;
        else if (op == TOK_POST_INC || op == TOK_PRE_INC)
                rez++;
        else if (op == TOK_POST_DEC || op == TOK_PRE_DEC)
                rez--;
        else if (op != TOK_UPLUS) {
                /* Binary operators */
                arith_t right_side_val;
                char bad_second_val;

                /* Binary operators need two arguments */
                if (top_of_stack == numstack)
                        goto err;
                /* ...and they pop one */
                NUMPTR = top_of_stack; /* this decrements NUMPTR */

                bad_second_val = top_of_stack->second_val_present;
                if (op == TOK_CONDITIONAL) { /* ? operation */
                        /* Make next if (...) protect against
                         * $((expr1 ? expr2)) - that is, missing ": expr" */
                        bad_second_val = !bad_second_val;
                }
                if (bad_second_val) {
                        /* Protect against $((expr <not_?_op> expr1 : expr2)) */
                        return "malformed ?: operator";
                }

                top_of_stack--; /* now points to left side */

                if (op != TOK_ASSIGN) {
                        /* Resolve left side value (unless the op is '=') */
                        err = arith_lookup_val(math_state, top_of_stack);
                        if (err)
                                return err;
                }

                right_side_val = rez;
                rez = top_of_stack->val;
                if (op == TOK_CONDITIONAL) /* ? operation */
                        rez = (rez ? right_side_val : top_of_stack[1].second_val);
                else if (op == TOK_CONDITIONAL_SEP) { /* : operation */
                        if (top_of_stack == numstack) {
                                /* Protect against $((expr : expr)) */
                                return "malformed ?: operator";
                        }
                        top_of_stack->second_val_present = op;
                        top_of_stack->second_val = right_side_val;
                }
                else if (op == TOK_BOR || op == TOK_OR_ASSIGN)
                        rez |= right_side_val;
                else if (op == TOK_OR)
                        rez = right_side_val || rez;
                else if (op == TOK_BAND || op == TOK_AND_ASSIGN)
                        rez &= right_side_val;
                else if (op == TOK_BXOR || op == TOK_XOR_ASSIGN)
                        rez ^= right_side_val;
                else if (op == TOK_AND)
                        rez = rez && right_side_val;
                else if (op == TOK_EQ)
                        rez = (rez == right_side_val);
                else if (op == TOK_NE)
                        rez = (rez != right_side_val);
                else if (op == TOK_GE)
                        rez = (rez >= right_side_val);
                else if (op == TOK_RSHIFT || op == TOK_RSHIFT_ASSIGN)
                        rez >>= right_side_val;
                else if (op == TOK_LSHIFT || op == TOK_LSHIFT_ASSIGN)
                        rez <<= right_side_val;
                else if (op == TOK_GT)
                        rez = (rez > right_side_val);
                else if (op == TOK_LT)
                        rez = (rez < right_side_val);
                else if (op == TOK_LE)
                        rez = (rez <= right_side_val);
                else if (op == TOK_MUL || op == TOK_MUL_ASSIGN)
                        rez *= right_side_val;
                else if (op == TOK_ADD || op == TOK_PLUS_ASSIGN)
                        rez += right_side_val;
                else if (op == TOK_SUB || op == TOK_MINUS_ASSIGN)
                        rez -= right_side_val;
                else if (op == TOK_ASSIGN || op == TOK_COMMA)
                        rez = right_side_val;
                else if (op == TOK_EXPONENT) {
                        arith_t c;
                        if (right_side_val < 0)
                                return "exponent less than 0";
                        c = 1;
                        while (--right_side_val >= 0)
                                c *= rez;
                        rez = c;
                }
                else if (right_side_val == 0)
                        return "divide by zero";
                else if (op == TOK_DIV || op == TOK_DIV_ASSIGN
                      || op == TOK_REM || op == TOK_REM_ASSIGN) {
                        /*
                         * bash 4.2.45 x86 64bit: SEGV on 'echo $((2**63 / -1))'
                         *
                         * MAX_NEGATIVE_INT / -1 = MAX_POSITIVE_INT+1
                         * and thus is not representable.
                         * Some CPUs segfault trying such op.
                         * Others overflow MAX_POSITIVE_INT+1 to
                         * MAX_NEGATIVE_INT (0x7fff+1 = 0x8000).
                         * Make sure to at least not SEGV here:
                         */
                        if (right_side_val == -1
                         && rez << 1 == 0 /* MAX_NEGATIVE_INT or 0 */
                        ) {
                                right_side_val = 1;
                        }
                        if (op == TOK_DIV || op == TOK_DIV_ASSIGN)
                                rez /= right_side_val;
                        else {
                                rez %= right_side_val;
                        }
                }
        }

        if (is_assign_op(op)) {
                char buf[sizeof(arith_t)*3 + 2];

                if (top_of_stack->var == NULL) {
                        /* Hmm, 1=2 ? */
//TODO: actually, bash allows ++7 but for some reason it evals to 7, not 8
                        goto err;
                }
                /* Save to shell variable */
                sprintf(buf, ARITH_FMT, rez);
                setvar(top_of_stack->var, buf);
                /* After saving, make previous value for v++ or v-- */
                if (op == TOK_POST_INC)
                        rez--;
                else if (op == TOK_POST_DEC)
                        rez++;
        }

        top_of_stack->val = rez;
        /* Erase var name, it is just a number now */
        top_of_stack->var = NULL;
        return NULL;
 err:
        return "arithmetic syntax error";
#undef NUMPTR
}

/* longest must be first */
static const char op_tokens[] ALIGN1 = {
        '<','<','=',0, TOK_LSHIFT_ASSIGN,
        '>','>','=',0, TOK_RSHIFT_ASSIGN,
        '<','<',    0, TOK_LSHIFT,
        '>','>',    0, TOK_RSHIFT,
        '|','|',    0, TOK_OR,
        '&','&',    0, TOK_AND,
        '!','=',    0, TOK_NE,
        '<','=',    0, TOK_LE,
        '>','=',    0, TOK_GE,
        '=','=',    0, TOK_EQ,
        '|','=',    0, TOK_OR_ASSIGN,
        '&','=',    0, TOK_AND_ASSIGN,
        '*','=',    0, TOK_MUL_ASSIGN,
        '/','=',    0, TOK_DIV_ASSIGN,
        '%','=',    0, TOK_REM_ASSIGN,
        '+','=',    0, TOK_PLUS_ASSIGN,
        '-','=',    0, TOK_MINUS_ASSIGN,
        '-','-',    0, TOK_POST_DEC,
        '^','=',    0, TOK_XOR_ASSIGN,
        '+','+',    0, TOK_POST_INC,
        '*','*',    0, TOK_EXPONENT,
        '!',        0, TOK_NOT,
        '<',        0, TOK_LT,
        '>',        0, TOK_GT,
        '=',        0, TOK_ASSIGN,
        '|',        0, TOK_BOR,
        '&',        0, TOK_BAND,
        '*',        0, TOK_MUL,
        '/',        0, TOK_DIV,
        '%',        0, TOK_REM,
        '+',        0, TOK_ADD,
        '-',        0, TOK_SUB,
        '^',        0, TOK_BXOR,
        /* uniq */
        '~',        0, TOK_BNOT,
        ',',        0, TOK_COMMA,
        '?',        0, TOK_CONDITIONAL,
        ':',        0, TOK_CONDITIONAL_SEP,
        ')',        0, TOK_RPAREN,
        '(',        0, TOK_LPAREN,
        0
};
#define ptr_to_rparen (&op_tokens[sizeof(op_tokens)-7])

#if ENABLE_FEATURE_SH_MATH_BASE
static arith_t strto_arith_t(const char *nptr, char **endptr)
{
        unsigned base;
        arith_t n;

# if ENABLE_FEATURE_SH_MATH_64
        n = strtoull(nptr, endptr, 0);
# else
        n = strtoul(nptr, endptr, 0);
# endif
        if (**endptr != '#'
         || (*nptr < '1' || *nptr > '9')
         || (n < 2 || n > 64)
        ) {
                return n;
        }

        /* It's "N#nnnn" or "NN#nnnn" syntax, NN can't start with 0,
         * NN is in 2..64 range.
         */
        base = (unsigned)n;
        n = 0;
        nptr = *endptr + 1;
        /* bash allows "N#" (empty "nnnn" part) */
        while (isdigit(*nptr)) {
                /* bash does not check for overflows */
                n = n * base + (*nptr++ - '0');
        }
        *endptr = (char*)nptr;
        return n;
}
#else /* !ENABLE_FEATURE_SH_MATH_BASE */
# if ENABLE_FEATURE_SH_MATH_64
#  define strto_arith_t(nptr, endptr) strtoull(nptr, endptr, 0)
# else
#  define strto_arith_t(nptr, endptr) strtoul(nptr, endptr, 0)
# endif
#endif

static arith_t FAST_FUNC
evaluate_string(arith_state_t *math_state, const char *expr)
{
        operator lasttok;
        const char *errmsg;
        const char *start_expr = expr = skip_whitespace(expr);
        unsigned expr_len = strlen(expr) + 2;
        /* Stack of integers */
        /* The proof that there can be no more than strlen(startbuf)/2+1
         * integers in any given correct or incorrect expression
         * is left as an exercise to the reader. */
        var_or_num_t *const numstack = alloca((expr_len / 2) * sizeof(numstack[0]));
        var_or_num_t *numstackptr = numstack;
        /* Stack of operator tokens */
        operator *const stack = alloca(expr_len * sizeof(stack[0]));
        operator *stackptr = stack;

        /* Start with a left paren */
        *stackptr++ = lasttok = TOK_LPAREN;
        errmsg = NULL;

        while (1) {
                const char *p;
                operator op;
                operator prec;
                char arithval;

                expr = skip_whitespace(expr);
                arithval = *expr;
                if (arithval == '\0') {
                        if (expr == start_expr) {
                                /* Null expression */
                                numstack->val = 0;
                                goto ret;
                        }

                        /* This is only reached after all tokens have been extracted from the
                         * input stream. If there are still tokens on the operator stack, they
                         * are to be applied in order. At the end, there should be a final
                         * result on the integer stack */

                        if (expr != ptr_to_rparen + 1) {
                                /* If we haven't done so already,
                                 * append a closing right paren
                                 * and let the loop process it */
                                expr = ptr_to_rparen;
                                continue;
                        }
                        /* At this point, we're done with the expression */
                        if (numstackptr != numstack + 1) {
                                /* ...but if there isn't, it's bad */
                                goto err;
                        }
                        if (numstack->var) {
                                /* expression is $((var)) only, lookup now */
                                errmsg = arith_lookup_val(math_state, numstack);
                        }
                        goto ret;
                }

                p = endofname(expr);
                if (p != expr) {
                        /* Name */
                        size_t var_name_size = (p-expr) + 1;  /* +1 for NUL */
                        numstackptr->var = alloca(var_name_size);
                        safe_strncpy(numstackptr->var, expr, var_name_size);
                        expr = p;
 num:
                        numstackptr->second_val_present = 0;
                        numstackptr++;
                        lasttok = TOK_NUM;
                        continue;
                }

                if (isdigit(arithval)) {
                        /* Number */
                        numstackptr->var = NULL;
                        errno = 0;
                        numstackptr->val = strto_arith_t(expr, (char**) &expr);
                        if (errno)
                                numstackptr->val = 0; /* bash compat */
                        goto num;
                }

                /* Should be an operator */

                /* Special case: NUM-- and NUM++ are not recognized if NUM
                 * is a literal number, not a variable. IOW:
                 * "a+++v" is a++ + v.
                 * "7+++v" is 7 + ++v, not 7++ + v.
                 */
                if (lasttok == TOK_NUM && !numstackptr[-1].var /* number literal */
                 && (expr[0] == '+' || expr[0] == '-')
                 && (expr[1] == expr[0])
                ) {
                        //bb_error_msg("special %c%c", expr[0], expr[0]);
                        op = (expr[0] == '+' ? TOK_ADD : TOK_SUB);
                        expr += 1;
                        goto tok_found1;
                }

                p = op_tokens;
                while (1) {
                        /* Compare expr to current op_tokens[] element */
                        const char *e = expr;
                        while (1) {
                                if (*p == '\0') {
                                        /* Match: operator is found */
                                        expr = e;
                                        goto tok_found;
                                }
                                if (*p != *e)
                                        break;
                                p++;
                                e++;
                        }
                        /* No match, go to next element of op_tokens[] */
                        while (*p)
                                p++;
                        p += 2; /* skip NUL and TOK_foo bytes */
                        if (*p == '\0') {
                                /* No next element, operator not found */
                                //math_state->syntax_error_at = expr;
                                goto err;
                        }
                }
 tok_found:
                op = p[1]; /* fetch TOK_foo value */
 tok_found1:
                /* NB: expr now points past the operator */

                /* post grammar: a++ reduce to num */
                if (lasttok == TOK_POST_INC || lasttok == TOK_POST_DEC)
                        lasttok = TOK_NUM;

                /* Plus and minus are binary (not unary) _only_ if the last
                 * token was a number, or a right paren (which pretends to be
                 * a number, since it evaluates to one). Think about it.
                 * It makes sense. */
                if (lasttok != TOK_NUM) {
                        switch (op) {
                        case TOK_ADD:
                                op = TOK_UPLUS;
                                break;
                        case TOK_SUB:
                                op = TOK_UMINUS;
                                break;
                        case TOK_POST_INC:
                                op = TOK_PRE_INC;
                                break;
                        case TOK_POST_DEC:
                                op = TOK_PRE_DEC;
                                break;
                        }
                }
                /* We don't want an unary operator to cause recursive descent on the
                 * stack, because there can be many in a row and it could cause an
                 * operator to be evaluated before its argument is pushed onto the
                 * integer stack.
                 * But for binary operators, "apply" everything on the operator
                 * stack until we find an operator with a lesser priority than the
                 * one we have just extracted. If op is right-associative,
                 * then stop "applying" on the equal priority too.
                 * Left paren is given the lowest priority so it will never be
                 * "applied" in this way.
                 */
                prec = PREC(op);
                if ((prec > 0 && prec < UNARYPREC) || prec == SPEC_PREC) {
                        /* not left paren or unary */
                        if (lasttok != TOK_NUM) {
                                /* binary op must be preceded by a num */
                                goto err;
                        }
                        while (stackptr != stack) {
                                operator prev_op = *--stackptr;
                                if (op == TOK_RPAREN) {
                                        /* The algorithm employed here is simple: while we don't
                                         * hit an open paren nor the bottom of the stack, pop
                                         * tokens and apply them */
                                        if (prev_op == TOK_LPAREN) {
                                                /* Any operator directly after a
                                                 * close paren should consider itself binary */
                                                lasttok = TOK_NUM;
                                                goto next;
                                        }
                                } else {
                                        operator prev_prec = PREC(prev_op);
                                        fix_assignment_prec(prec);
                                        fix_assignment_prec(prev_prec);
                                        if (prev_prec < prec
                                         || (prev_prec == prec && is_right_associative(prec))
                                        ) {
                                                stackptr++;
                                                break;
                                        }
                                }
                                errmsg = arith_apply(math_state, prev_op, numstack, &numstackptr);
                                if (errmsg)
                                        goto err_with_custom_msg;
                        }
                        if (op == TOK_RPAREN)
                                goto err;
                }

                /* Push this operator to the stack and remember it */
                *stackptr++ = lasttok = op;
 next: ;
        } /* while (1) */

 err:
        errmsg = "arithmetic syntax error";
 err_with_custom_msg:
        numstack->val = -1;
 ret:
        math_state->errmsg = errmsg;
        return numstack->val;
}

arith_t FAST_FUNC
arith(arith_state_t *math_state, const char *expr)
{
        math_state->errmsg = NULL;
        math_state->list_of_recursed_names = NULL;
        return evaluate_string(math_state, expr);
}

/*
 * Copyright (c) 1989, 1991, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Kenneth Almquist.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ''AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */