在simclist链接列表库中,我遇到了一个问题,即在函数list_findpos()
中出现除零。通常我会犹豫是否要修改一个广泛使用的第三方库,并且必须有充分的理由说明它为什么会这样做(我没有排除库的使用不正确)。该函数定义为:
/* set tmp to point to element at index posstart in l */
static inline struct list_entry_s *list_findpos(const list_t *restrict l, int posstart) {
struct list_entry_s *ptr;
float x;
int i;
/* accept 1 slot overflow for fetching head and tail sentinels */
if (posstart < -1 || posstart > (int)l->numels) return NULL;
x = (float)(posstart+1) / l->numels;
if (x <= 0.25) {
/* first quarter: get to posstart from head */
for (i = -1, ptr = l->head_sentinel; i < posstart; ptr = ptr->next, i++);
} else if (x < 0.5) {
/* second quarter: get to posstart from mid */
for (i = (l->numels-1)/2, ptr = l->mid; i > posstart; ptr = ptr->prev, i--);
} else if (x <= 0.75) {
/* third quarter: get to posstart from mid */
for (i = (l->numels-1)/2, ptr = l->mid; i < posstart; ptr = ptr->next, i++);
} else {
/* fourth quarter: get to posstart from tail */
for (i = l->numels, ptr = l->tail_sentinel; i > posstart; ptr = ptr->prev, i--);
}
return ptr;
}
如果l->numels
是0
,那么第9行的表达式就是个问题。否则代码运行正常(没有泄漏或段错误),但英特尔检查员说这条线上出现了除零。建议的更改是:
/* set tmp to point to element at index posstart in l */
static inline struct list_entry_s *list_findpos(const list_t *restrict l, int posstart) {
struct list_entry_s *ptr;
float x;
int i;
/* accept 1 slot overflow for fetching head and tail sentinels */
if (posstart < -1 || posstart > (int)l->numels) return NULL;
if (l->numels == 0){ //avoid division-by-zero on first element
ptr = l->head_sentinel;
}
else{
x = (float)(posstart + 1) / l->numels;
if (x <= 0.25) {
/* first quarter: get to posstart from head */
for (i = -1, ptr = l->head_sentinel; i < posstart; ptr = ptr->next, i++);
}
else if (x < 0.5) {
/* second quarter: get to posstart from mid */
for (i = (l->numels - 1) / 2, ptr = l->mid; i > posstart; ptr = ptr->prev, i--);
}
else if (x <= 0.75) {
/* third quarter: get to posstart from mid */
for (i = (l->numels - 1) / 2, ptr = l->mid; i < posstart; ptr = ptr->next, i++);
}
else {
/* fourth quarter: get to posstart from tail */
for (i = l->numels, ptr = l->tail_sentinel; i > posstart; ptr = ptr->prev, i--);
}
}
return ptr;
}
想知道是否有人可以对使用simclist的经验发表评论?
修改
list_findpos
不是API函数;相反,它是一个内部功能。导致问题的电话序列是:
/* ... */
list_init(...)
list_attributes_copy(...)
list_append(...) /* <---- list_findpos() is called here, divide by zero */
答案 0 :(得分:0)
此功能不是库API的一部分;它完全是内部的。为了解决这个问题,图书馆的作者/维护者需要知道的是你所做的API调用序列导致它失败。