postfix... 이거 어떤책에 나오는 소스인가요?

자료구조시간에, 피곤해서 잠깐 자고있어났더니..
postfix 라는걸 했더군요...
책에도 없는 소스를 주석 달아오라네요..^^
뒤적이다보니 외국사이트에도 올라가있고,.. 꽤 알려진 책에서 나온 소스같던데, 어떤 책인지 좀 알려주시면 감사~ ^^;

#include <stdio.h>
#include <stdlib.h>

#define MAXCOLS 60
#define TRUE 1
#define FALSE 0

#define PLUS 1
#define MINUS 1
#define MUL 2
#define DIV 2

struct stack
{
	int top;
	char items[MAXCOLS];
};

int empty(struct stack *ps)
{
	if(ps->top == -1)
		return TRUE;
	else
		return FALSE;
}

char pop(struct stack *ps)
{
	if(empty(ps))
	{
		printf("%s", "stack underflow");
		exit(1);
	}
	return (ps->items[ps->top--]);
}

void popandtest(struct stack *ps, char *px, int *pund)
{
	if(empty(ps))
	{
		*pund = TRUE;
		return;
	}
	*pund = FALSE;
	*px = ps->items[ps->top--];
	return;
}

void push(struct stack *ps, char x)
{
	ps->items[++(ps->top)] = x;
	return;
}

int isoperand(char ch)
{
	if((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') || (ch >= '0' && ch <= '9'))
		return TRUE;
	return FALSE;
}

int prcd(char op1, char op2)
{
	switch(op1)
	{
		case '+' :
			op1 = PLUS;
			break;
		case '-' :
			op1 = MINUS;
			break;
		case '*' :
			op1 = MUL;
			break;
		case '/' :
			op1 = DIV;
			break;
	}

	switch(op2)
	{
		case '+' :
			op2 = PLUS;
			break;
		case '-' :
			op2 = MINUS;
			break;
		case '*' :
			op2 = MUL;
			break;
		case '/' :
			op2 = DIV;
			break;
	}

	if(op1 == '(')
		return FALSE;
	if(op2 == '(')
		return FALSE;
	if(op2 == ')')
		return TRUE;

	if(op1 >= op2)
		return TRUE;
	else 
		return FALSE;
}

void postfix(char in[], char po[])
{
	int position, und;
	int outpos = 0;
	char topsymb = '+';
	char symb;
	struct stack opstk;
	opstk.top = -1;

	for(position = 0; (symb = in[position]) != '\0'; position++)
		if(isoperand(symb))
			po[outpos++] = symb;
		else
		{
			popandtest(&opstk, &topsymb, &und);
			while(!und && prcd(topsymb, symb))
			{
				po[outpos++] = topsymb;
				popandtest(&opstk, &topsymb, &und);
			}
			if(!und)
				push(&opstk, topsymb);
			if(und || (symb != ')'))
				push(&opstk, symb);
			else
				topsymb = pop(&opstk);
		}
		while(!empty(&opstk))
			po[outpos++] = pop(&opstk);
		po[outpos] = '\0';
		return;
}

void main(void)
{
	char infix[MAXCOLS];
	char postr[MAXCOLS];
	int pos = 0;

	while((infix[pos++] = getchar()) != '\n');
	infix[--pos] = '\0';
	printf("%s%s", "the original infix expression is ", infix);
	postfix(infix, postr);
	printf("\n%s\n", postr);
}