user: 提供的汇编代码用C语言表示会是什么样子：

```asm
<ff_dm_quad>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x88,%rsp
  mov    0xc0(%rsp),%rax
  mov    %rdi,0x50(%rsp)
  mov    %esi,0x24(%rsp)
  mov    %rax,0x40(%rsp)
  mov    0xc8(%rsp),%rax
  movsd  %xmm0,0x28(%rsp)
  mov    %rax,0x48(%rsp)
  mov    %fs:0x28,%rax
  mov    %rax,0x78(%rsp)
  xor    %eax,%eax
  test   %rdi,%rdi
  je     L8
  lea    0x0(,%rdi,8),%rax
  mov    %rdx,%rbp
  lea    0x60(%rsp),%r13
  mov    %r9,%r12
  add    %rax,%r8
  mov    %rax,0x58(%rsp)
  lea    (%rcx,%rax,1),%rbx
  mov    %r8,0x10(%rsp)
  movq   $0x0,(%rsp)
  movq   $0x0,0x8(%rsp)
  nopl   0x0(%rax)
L89:
  mov    (%rsp),%rax
  add    $0x1,%rax
  mov    %rax,0x18(%rsp)
  cmp    %rax,0x50(%rsp)
  je     L51
  mov    0x18(%rsp),%rax
  xor    %r14d,%r14d
  lea    (%rax,%rax,2),%rax
  lea    0x0(%rbp,%rax,8),%r15
  jmp    L49
  xchg   %ax,%ax
L63:
  mov    0x48(%rsp),%r8
  mov    0x40(%rsp),%rcx
  mov    %r13,%rdx
  mov    %r15,%rdi
  call   <distance_delta_periodic@plt>
  movsd  0x30(%rsp),%xmm2
  movsd  0x38(%rsp),%xmm4
  movapd %xmm0,%xmm1
L74:
  movsd  0x28(%rsp),%xmm5
  movapd %xmm1,%xmm3
  subsd  %xmm2,%xmm3
  movapd %xmm5,%xmm0
  mulsd  %xmm4,%xmm0
  mulsd  %xmm3,%xmm0
  mulsd  %xmm3,%xmm0
  addsd  0x8(%rsp),%xmm0
  movsd  %xmm0,0x8(%rsp)
  test   %r12,%r12
  je     L26
  movapd %xmm5,%xmm0
  mov    0x18(%rsp),%rdi
  mov    %r12,%r8
  mov    %r13,%rcx
  addsd  %xmm5,%xmm0
  mov    %rbp,%rdx
  mov    %r14,%rsi
  mulsd  %xmm4,%xmm0
  mulsd  %xmm3,%xmm0
  divsd  %xmm1,%xmm0
  call   <add_grad@plt>
L26:
  lea    0x1(%r14),%rax
  cmp    %r14,(%rsp)
  je     L6
  mov    %rax,%r14
L49:
  movsd  (%rbx,%r14,8),%xmm2
  pxor   %xmm6,%xmm6
  comisd %xmm6,%xmm2
  jbe    L26
  mov    0x10(%rsp),%rax
  movsd  %xmm2,0x30(%rsp)
  movsd  (%rax,%r14,8),%xmm4
  lea    (%r14,%r14,2),%rax
  lea    0x0(%rbp,%rax,8),%rsi
  mov    0x24(%rsp),%eax
  movsd  %xmm4,0x38(%rsp)
  test   %eax,%eax
  jne    L63
  mov    %r13,%rdx
  mov    %r15,%rdi
  call   <distance_delta@plt>
  movsd  0x38(%rsp),%xmm4
  movsd  0x30(%rsp),%xmm2
  movapd %xmm0,%xmm1
  jmp    L74
  nopw   0x0(%rax,%rax,1)
L6:
  mov    0x58(%rsp),%rdx
  mov    0x18(%rsp),%rax
  add    %rdx,0x10(%rsp)
  mov    %rax,(%rsp)
  add    %rdx,%rbx
  jmp    L89
L8:
  pxor   %xmm7,%xmm7
  movsd  %xmm7,0x8(%rsp)
  nopl   (%rax)
L51:
  mov    0x78(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L40
  movsd  0x8(%rsp),%xmm0
  add    $0x88,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L40:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
double ff_dm_quad(size_t natom, int periodic, double *cor, double *dm0, double *dmk, double amp, double *gradient, double *matrix, double *reciprocal) {
  size_t i, j;
  double delta[3], d, d0, k, tmp, result;
  result = 0.0;
  for (i = 0; i < natom; i++) {
    for (j = 0; j < i; j++) {
      d0 = dm0[i * natom + j];
      k = dmk[i * natom + j];
      if (d0 > 0) {
        if (periodic) {
          d = distance_delta_periodic(cor + 3 * i, cor + 3 * j, delta, matrix, reciprocal);
        } else {
          d = distance_delta(cor + 3 * i, cor + 3 * j, delta);
        }
        tmp = (d - d0);
        result += amp * k * tmp * tmp;
        if (gradient != NULL) {
          tmp = 2 * amp * k * tmp / d;
          add_grad(i, j, tmp, cor, delta, gradient);
        }
      }
    }
  }
  return result;
}
```