/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "libbb.h"
#include <math.h>

/* Tiny RPN calculator, because "expr" didn't give me bitwise operations. */


struct globals {
        unsigned pointer;
        unsigned base;
        double stack[1];
} FIX_ALIASING;
enum { STACK_SIZE = (COMMON_BUFSIZE - offsetof(struct globals, stack)) / sizeof(double) };
#define G (*(struct globals*)&bb_common_bufsiz1)
#define pointer   (G.pointer   )
#define base      (G.base      )
#define stack     (G.stack     )
#define INIT_G() do { \
        base = 10; \
} while (0)


static void push(double a)
{
        if (pointer >= STACK_SIZE)
                bb_error_msg_and_die("stack overflow");
        stack[pointer++] = a;
}

static double pop(void)
{
        if (pointer == 0)
                bb_error_msg_and_die("stack underflow");
        return stack[--pointer];
}

static void add(void)
{
        push(pop() + pop());
}

static void sub(void)
{
        double subtrahend = pop();

        push(pop() - subtrahend);
}

static void mul(void)
{
        push(pop() * pop());
}

#if ENABLE_FEATURE_DC_LIBM
static void power(void)
{
        double topower = pop();

        push(pow(pop(), topower));
}
#endif

static void divide(void)
{
        double divisor = pop();

        push(pop() / divisor);
}

static void mod(void)
{
        unsigned d = pop();

        push((unsigned) pop() % d);
}

static void and(void)
{
        push((unsigned) pop() & (unsigned) pop());
}

static void or(void)
{
        push((unsigned) pop() | (unsigned) pop());
}

static void eor(void)
{
        push((unsigned) pop() ^ (unsigned) pop());
}

static void not(void)
{
        push(~(unsigned) pop());
}

static void set_output_base(void)
{
        static const char bases[] ALIGN1 = { 2, 8, 10, 16, 0 };
        unsigned b = (unsigned)pop();

        base = *strchrnul(bases, b);
        if (base == 0) {
                bb_error_msg("error, base %u is not supported", b);
                base = 10;
        }
}

static void print_base(double print)
{
        unsigned x, i;

        if (base == 10) {
                printf("%g\n", print);
                return;
        }

        x = (unsigned)print;
        switch (base) {
        case 16:
                printf("%x\n", x);
                break;
        case 8:
                printf("%o\n", x);
                break;
        default: /* base 2 */
                i = (unsigned)INT_MAX + 1;
                do {
                        if (x & i) break;
                        i >>= 1;
                } while (i > 1);
                do {
                        bb_putchar('1' - !(x & i));
                        i >>= 1;
                } while (i);
                bb_putchar('\n');
        }
}

static void print_stack_no_pop(void)
{
        unsigned i = pointer;
        while (i)
                print_base(stack[--i]);
}

static void print_no_pop(void)
{
        print_base(stack[pointer-1]);
}

struct op {
        const char name[4];
        void (*function) (void);
};

static const struct op operators[] = {
        {"+",   add},
        {"add", add},
        {"-",   sub},
        {"sub", sub},
        {"*",   mul},
        {"mul", mul},
        {"/",   divide},
        {"div", divide},
#if ENABLE_FEATURE_DC_LIBM
        {"**",  power},
        {"exp", power},
        {"pow", power},
#endif
        {"%",   mod},
        {"mod", mod},
        {"and", and},
        {"or",  or},
        {"not", not},
        {"eor", eor},
        {"xor", eor},
        {"p", print_no_pop},
        {"f", print_stack_no_pop},
        {"o", set_output_base},
        { "", NULL }
};

static void stack_machine(const char *argument)
{
        char *endPointer;
        double d;
        const struct op *o = operators;

        d = strtod(argument, &endPointer);

        if (endPointer != argument && *endPointer == '\0') {
                push(d);
                return;
        }

        while (o->function) {
                if (strcmp(o->name, argument) == 0) {
                        o->function();
                        return;
                }
                o++;
        }
        bb_error_msg_and_die("syntax error at '%s'", argument);
}

/* return pointer to next token in buffer and set *buffer to one char
 * past the end of the above mentioned token
 */
static char *get_token(char **buffer)
{
        char *current = skip_whitespace(*buffer);
        if (*current != '\0') {
                *buffer = skip_non_whitespace(current);
                return current;
        }
        return NULL;
}

int dc_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dc_main(int argc UNUSED_PARAM, char **argv)
{
        INIT_G();

        argv++;
        if (!argv[0]) {
                /* take stuff from stdin if no args are given */
                char *line;
                char *cursor;
                char *token;
                while ((line = xmalloc_fgetline(stdin)) != NULL) {
                        cursor = line;
                        while (1) {
                                token = get_token(&cursor);
                                if (!token)
                                        break;
                                *cursor++ = '\0';
                                stack_machine(token);
                        }
                        free(line);
                }
        } else {
                // why? it breaks "dc -2 2 * p"
                //if (argv[0][0] == '-')
                //      bb_show_usage();
                do {
                        stack_machine(*argv);
                } while (*++argv);
        }
        return EXIT_SUCCESS;
}