+ ssize_t base;
+ struct cookie *c = f->cookie;
+ if (whence>2U) {
+fail:
+ errno = EINVAL;
+ return -1;
+ }
+ base = (size_t [3]){0, c->pos, c->len}[whence];
+ if (off < -base || off > SSIZE_MAX-base) goto fail;
+ return c->pos = base+off;
+}
+
+static size_t mread(FILE *f, unsigned char *buf, size_t len)
+{
+ struct cookie *c = f->cookie;
+ size_t rem = c->size - c->pos;
+ if (len > rem) len = rem;
+ memcpy(buf, c->buf+c->pos, len);
+ c->pos += len;
+ rem -= len;
+ if (rem > f->buf_size) rem = f->buf_size;
+ f->rpos = f->buf;
+ f->rend = f->buf + rem;
+ memcpy(f->rpos, c->buf+c->pos, rem);
+ if (!len) f->flags |= F_EOF;
+ return len;
+}
+
+static size_t mwrite(FILE *f, const unsigned char *buf, size_t len)
+{
+ struct cookie *c = f->cookie;
+ size_t rem;
+ size_t len2 = f->wpos - f->wbase;
+ if (len2) {
+ f->wpos = f->wbase;
+ if (mwrite(f, f->wpos, len2) < len2) return 0;
+ }
+ if (c->mode == 'a') c->pos = c->size;
+ rem = c->size - c->pos;
+ if (len > rem) len = rem;
+ memcpy(c->buf+c->pos, buf, len);
+ c->pos += len;
+ if (c->pos >= c->len) c->len = c->pos;
+ c->buf[c->len==c->size ? c->len-1 : c->len] = 0;
+ return len;
+}
+
+static int mclose(FILE *m)
+{
+ return 0;