#ifndef caller_save_h
#define caller_save_h

namespace as
{

//--------------------------------------------------------------------
// class caller_save
//--------------------------------------------------------------------

class caller_save // SystemV AMD64 ABI
{
public:
    enum when {first = 0, next};

    caller_save() noexcept = default;

    when __attribute__((naked,noinline,returns_twice)) get() noexcept
    {
        asm volatile("mov (%%rsp),%%rax  \n"
                     "mov %%rax,%0       \n"
                     "lea 8(%%rsp),%%rax \n"
                     "mov %%rax,%1       \n"
                     "mov %%rbp,%2       \n"
                     "mov %%rbx,%3       \n"
                     "mov %%r12,%4       \n"
                     "mov %%r13,%5       \n"
                     "mov %%r14,%6       \n"
                     "mov %%r15,%7       \n"
                     "xor %%rax,%%rax    \n"
                     "ret                \n"
                     :"=m"(rip), "=m"(rsp), "=m"(rbp), "=m"(rbx), 
                      "=m"(r12), "=m"(r13), "=m"(r14), "=m"(r15)
                     :
                     :"rax","memory");
    }

    void __attribute__((naked,noinline,noreturn)) set(when ret = next) const noexcept
    {
        asm volatile("mov %1,%%rsp \n"
                     "mov %2,%%rbp \n"
                     "mov %3,%%rbx \n"
                     "mov %4,%%r12 \n"
                     "mov %5,%%r13 \n"
                     "mov %6,%%r14 \n"
                     "mov %7,%%r15 \n"
                     "jmp *%0      \n"
                     :
                     :"m"(rip), "m"(rsp), "m"(rbp), "m"(rbx), 
                      "m"(r12), "m"(r13), "m"(r14), "m"(r15),
                      "a"(ret));
    }

private:
    void *rip, *rsp, *rbp, *rbx, *r12, *r13, *r14, *r15; // SystemV AMD64 ABI

}; // caller_save

//--------------------------------------------------------------------

} // namespace as

#endif // caller_save_h