deque

### Summary:

type-preserving resizing circular deque

### Author:

Dan Good <[email protected]>

### Description:

This is a deque (double-ended queue, pronounced deck) implementation using a resizing circular buffer. At steady state, deque operations can proceed perpetually without mallocing. The initial capacity must be specified and is a lower bound when shrinking. Buffer capacity is doubled at enqueue to a full deque. Shrink behavior choices are never shrink, shrink to minimum when the queue is empty, or shrink by half when the queue is at 20% of capacity. Operation names are in the Perl/Ruby style.

### Example:

// Evaluates arithmetic expressions using Dijkstra's two-stack algorithm.
// Original: http://algs4.cs.princeton.edu/13stacks/EvaluateDeluxe.java.html
#define _XOPEN_SOURCE 700 // only for getline(3) in this demo
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <err.h>
#include <ccan/deque/deque.h>

static double eval(char op, double a, double b)
{
switch (op) {
case '+': return a + b;
case '-': return a - b;
case '/': return a / b;
case '*': return a * b;
}
}

char opchr[] = { '(', ')', '+', '-', '*', '/' };
int  opprc[] = {  0 ,  0 ,  1 ,  1 ,  2 ,  2  };

static int precedence(char op)
{
int i;
for (i = 0; i < sizeof(opchr); i++)
if (opchr[i] == op)
return opprc[i];
return -1;
}

#define ok(x) ({ int n = (x); if (n == -1) err(1, "%s", #x); n; })

int main(int argc, char *argv[])
{
DEQ_WRAP(char) *ops;
DEQ_WRAP(double) *vals;
char *ln = NULL, *p, op;
size_t lnsz = 0;
double a, b;
int n;

ok(deq_new(ops,  8, DEQ_NO_SHRINK));
ok(deq_new(vals, 8, DEQ_NO_SHRINK));

while (getline(&ln, &lnsz, stdin) > 0) {

for (p = ln; *p; p++) {
if (isspace(*p))
continue;

if (precedence(*p) == -1) {
if (sscanf(p, "%lf%n", &a, &n) != 1)
errx(1, "parse fail: %s", p);
ok(deq_push(vals, a));
p += n - 1;
continue;
}

while (1) {
if (*p == '(' || deq_last(ops, &op) == 0 || (precedence(*p) > precedence(op))) {
ok(deq_push(ops, *p));
break;
}

ok(deq_pop(ops, &op));

if (op == '(') {
assert(*p == ')');
break;
}
else {
if (deq_len(vals) < 2)
errx(1, "out of values");
ok(deq_pop(vals, &b));
ok(deq_pop(vals, &a));
ok(deq_push(vals, eval(op, a, b)));
}
}
}

while (ok(deq_pop(ops, &op)) == 1) {
if (deq_len(vals) < 2)
errx(1, "out of values");
ok(deq_pop(vals, &b));
ok(deq_pop(vals, &a));
ok(deq_push(vals, eval(op, a, b)));
}

if ((n = deq_len(vals)) != 1)
errx(1, "wrong number of values: %d", n);

ok(deq_pop(vals, &a));
printf("%.lf\n", a);
}

if (ferror(stdin))
err(1, "getline");

deq_free(ops);
deq_free(vals);
free(ln);
exit(0);
}