#if __LP64__
typedef uint32_t mask_t;  // x86_64 & arm64 asm are less efficient with 16-bits
#else
typedef uint16_t mask_t;
#endif

bucket_t数据结构

struct bucket_t {
  //sel作为key
    inline SEL sel() const { return _sel.load(memory_order::memory_order_relaxed); }

//imp作为value
    inline IMP imp(Class cls) const {
        uintptr_t imp = _imp.load(memory_order::memory_order_relaxed);
        if (!imp) return nil;
#if CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_PTRAUTH
        SEL sel = _sel.load(memory_order::memory_order_relaxed);
        return (IMP)
            ptrauth_auth_and_resign((const void *)imp,
                                    ptrauth_key_process_dependent_code,
                                    modifierForSEL(sel, cls),
                                    ptrauth_key_function_pointer, 0);
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_ISA_XOR
        return (IMP)(imp ^ (uintptr_t)cls);
#elif CACHE_IMP_ENCODING == CACHE_IMP_ENCODING_NONE
        return (IMP)imp;
#else
#error Unknown method cache IMP encoding.
#endif
    }
};

cache_t数据结构

struct cache_t {
      struct bucket_t *buckets();  //
      mask_t mask();        //数组（buckets）长度 - 1
      mask_t occupied();  //已缓存方法数
};