1 files changed, 149 insertions, 0 deletions
diff --git a/math.c b/math.c
new file mode 100644
index 0000000..5c1560a
--- /dev/null
+++ b/math.c
@@ -0,0 +1,149 @@
+#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(struct FileInfo * i, int argc, char * * argv)
+{
+	while ( argc >= 2 ) {
+		stack_machine(argv[1]);
+		argv++;
+		argc--;
+	}
+	stack_machine(0);
+	return 0;
+}