busybox/math.c

#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. */

const char			math_usage[] = "math expression ...";

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",	add	},
	{	"and",	and	},
	{	"div",	divide	},
	{	"eor",	eor	},
	{	"mul",	mul	},
	{	"not",	not	},
	{	"or",	or	},
	{	"sub",	sub	},
	{	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)
{
	while ( argc >= 2 ) {
		stack_machine(argv[1]);
		argv++;
		argc--;
	}
	stack_machine(0);
	return 0;
}