max.c

static inline size_t max_size_n(const size_t *values, size_t count) {
  size_t max = values[0];
  for (size_t i = 1; i < count; ++i) 
     if (values[i] > max) max = values[i];
  return max;
}

#define MAX_SIZE(...)                                      \
  max_size_n((const size_t[]){__VA_ARGS__},                \
  sizeof((const size_t[]){__VA_ARGS__}) / sizeof(size_t))  \

mm.c

// https://github.com/sharifsegfaults/nalloc/blob/7f023ccbb6f82245ab3a284382e7e018311d7d94/mm.c#L361-L364

size_t expansion_size = ALIGN(MAX_SIZE(
  (size_t)(EXPANSION_FACTOR * mem_heapsize()),
  sizeof(AllocBlockHeader) + size - recyclable_space,
  sizeof(FreeBlockHeader) + sizeof(BlockFooter)
));