/* 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. */

enum { STACK_SIZE = COMMON_BUFSIZE / sizeof(double) };

#define stack ((double*)&bb_common_bufsiz1)
static unsigned int pointer;
static unsigned char base;

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());
}

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)) {
		bb_error_msg("error, base %d is not supported", 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[4];
	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}
};

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;

	current = skip_whitespace(*buffer);
	if (*current != 0) {
		start = current;
		current = skip_non_whitespace(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) MAIN_EXTERNALLY_VISIBLE;
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 = xmalloc_getline(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;
}