busybox/math.c

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

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

static const char math_usage[] = "math expression ...\n\n"
		"This is a Tiny RPN calculator that understands the\n"
		"following operations: +, -, /, *, and, or, not, eor.\n"
		"i.e. 'math 2 2 add' -> 4, and 'math 8 8 \\* 2 2 + /' -> 16\n";

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

static void push(double a)
{
	if (pointer >= (sizeof(stack) / sizeof(*stack))) {
		fprintf(stderr, "math: stack overflow\n");
		exit(-1);
	} else
		stack[pointer++] = a;
}

static double pop()
{
	if (pointer == 0) {
		fprintf(stderr, "math: stack underflow\n");
		exit(-1);
	}
	return stack[--pointer];
}

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

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

	push(pop() - subtrahend);
}

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

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

	push(pop() / divisor);
}

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

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

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

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

static void print()
{
	printf("%g\n", pop());
}

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

static const struct op operators[] = {
	{"+", add},
	{"-", sub},
	{"*", mul},
	{"/", divide},
	{"and", and},
	{"or", or},
	{"not", not},
	{"eor", eor},
	{0, 0}
};

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

	if (argument == 0) {
		print();
		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++;
	}
	fprintf(stderr, "math: %s: syntax error.\n", argument);
	exit(-1);
}

int math_main(int argc, char **argv)
{
	if (argc < 1 || *argv[1]=='-')
		usage(math_usage);
	while (argc >= 2) {
		stack_machine(argv[1]);
		argv++;
		argc--;
	}
	stack_machine(0);
	exit( TRUE);
}