LibC: bsearch fix for large arrays (SerenityOS#3138)

Implement unsigned arithmetic to compute middle without causing overflow.
And without mixed signed/unsigned operations.

Libraries/LibC/stdlib.cpp

@@ -745,18 +745,17 @@ char* mkdtemp(char* pattern)
 
 void* bsearch(const void* key, const void* base, size_t nmemb, size_t size, int (*compar)(const void*, const void*))
 {
- int low = 0;
- int high = nmemb - 1;
- while (low <= high) {
- int middle = (low + high) / 2;
- void* middle_memb = const_cast<char*>((const char*)base + middle * size);
+ char* start = static_cast<char*>(const_cast<void*>(base));
+ while (nmemb > 0) {
+ char* middle_memb = start + (nmemb / 2) * size;
  int comparison = compar(key, middle_memb);
- if (comparison < 0)
- high = middle - 1;
- else if (comparison > 0)
- low = middle + 1;
- else
+ if (comparison == 0)
  return middle_memb;
+ else if (comparison > 0) {
+ start = middle_memb + size;
+ --nmemb;
+ }
+ nmemb /= 2;
  }
 
  return NULL;