source: MondoRescue/branches/2.2.2/mindi-busybox/miscutils/dc.c@ 1247

/* vi: set sw=4 ts=4: */
#include "busybox.h"
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <math.h>

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

static double stack[100];
static unsigned int pointer;
static unsigned char base;

static void push(double a)
{
    if (pointer >= (sizeof(stack) / sizeof(*stack)))
        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());
}

static void power(void)
{
    double topower = pop();

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

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

    push(pop() / divisor);
}

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

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

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

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

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

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

static void set_output_base(void)
{
    base=(unsigned char)pop();
    if ((base != 10) && (base != 16)) {
        fprintf(stderr, "Error: base = %d is not supported.\n", base);
        base=10;
    }
}

static void print_base(double print)
{
    if (base == 16)
        printf("%x\n", (unsigned int)print);
    else
    printf("%g\n", print);
}

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

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

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

static const struct op operators[] = {
    {"+",   add},
    {"add", add},
    {"-",   sub},
    {"sub", sub},
    {"*",   mul},
    {"mul", mul},
    {"/",   divide},
    {"div", divide},
    {"**",  power},
    {"exp", power},
    {"pow", power},
    {"%",   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},
    {0,     0}
};

static void stack_machine(const char *argument)
{
    char *endPointer = 0;
    double d;
    const struct op *o = operators;

    if (argument == 0)
        return;

    d = strtod(argument, &endPointer);

    if (endPointer != argument) {
        push(d);
        return;
    }

    while (o->name != 0) {
        if (strcmp(o->name, argument) == 0) {
            (*(o->function)) ();
            return;
        }
        o++;
    }
    bb_error_msg_and_die("%s: syntax error.", 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 *start   = NULL;
    char *current = *buffer;

    while (isspace(*current)) { current++; }
    if (*current != 0) {
        start = current;
        while (!isspace(*current) && *current != 0) { current++; }
        *buffer = current;
    }
    return start;
}

/* In Perl one might say, scalar m|\s*(\S+)\s*|g */
static int number_of_tokens(char *buffer)
{
    int   i = 0;
    char *b = buffer;
    while (get_token(&b)) { i++; }
    return i;
}

int dc_main(int argc, char **argv)
{
    /* take stuff from stdin if no args are given */
    if (argc <= 1) {
        int i, len;
        char *line   = NULL;
        char *cursor = NULL;
        char *token  = NULL;
        while ((line = bb_get_chomped_line_from_file(stdin))) {
            cursor = line;
            len = number_of_tokens(line);
            for (i = 0; i < len; i++) {
                token = get_token(&cursor);
                *cursor++ = 0;
                stack_machine(token);
            }
            free(line);
        }
    } else {
        if (*argv[1]=='-')
            bb_show_usage();
        while (argc >= 2) {
            stack_machine(argv[1]);
            argv++;
            argc--;
        }
    }
    return EXIT_SUCCESS;
}