user: 下面的汇编指令对应的C源代码是什么：

```asm
<backrow>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  movslq %edi,%r12
  push   %rbp
  lea    -0x1(%r12),%ebp
  push   %rbx
  mov    %rdx,%rbx
  sub    $0x18,%rsp
  test   %ecx,%ecx
  jne    L180
  test   %ebp,%ebp
  js     L50
  movslq %ebp,%rdx
  movslq %r12d,%rcx
  mov    %r12d,%r14d
  imul   $0x1908,%rcx,%rcx
  lea    (%rbx,%rdx,8),%rbp
  lea    (%rdx,%rdx,4),%rdx
  lea    (%rdx,%rdx,4),%r13
  shl    $0x8,%r13
  lea    -0x1908(%rsi,%rcx,1),%r15
  add    %rsi,%r13
  nopl   0x0(%rax,%rax,1)
L7:
  cmp    %r14d,%r12d
  jle    L116
  movsd  0x0(%rbp),%xmm1
  movslq %r14d,%rax
  nopl   (%rax)
L99:
  movsd  0x0(%r13,%rax,8),%xmm0
  mulsd  (%rbx,%rax,8),%xmm0
  add    $0x1,%rax
  subsd  %xmm0,%xmm1
  movsd  %xmm1,0x0(%rbp)
  cmp    %eax,%r12d
  jg     L99
L116:
  movsd  (%r15),%xmm0
  call   <is_zero@plt>
  test   %rax,%rax
  jne    L100
  movsd  0x0(%rbp),%xmm0
  sub    $0x8,%rbp
  divsd  (%r15),%xmm0
  sub    $0x1900,%r13
  movsd  %xmm0,0x8(%rbp)
  sub    $0x1908,%r15
  sub    $0x1,%r14d
  jne    L7
L50:
  add    $0x18,%rsp
  xor    %eax,%eax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   0x0(%rax)
L180:
  test   %ebp,%ebp
  js     L50
  imul   $0x1908,%r12,%rcx
  lea    0x8(%rdx),%rax
  movslq %ebp,%r14
  mov    %rax,0x8(%rsp)
  lea    -0x1908(%rsi,%rcx,1),%r15
  lea    (%r12,%r12,4),%rcx
  lea    (%rcx,%rcx,4),%rcx
  movsd  (%r15),%xmm0
  lea    (%rdx,%r12,8),%r12
  shl    $0x8,%rcx
  lea    -0x1900(%rsi,%rcx,1),%r13
  call   <is_zero@plt>
  test   %rax,%rax
  jne    L100
  nopw   0x0(%rax,%rax,1)
L38:
  movsd  -0x8(%r12),%xmm0
  lea    -0x1(%rbp),%ecx
  divsd  (%r15),%xmm0
  movsd  %xmm0,-0x8(%r12)
  test   %r14d,%r14d
  jle    L71
  mulsd  0x0(%r13),%xmm0
  movsd  (%rbx),%xmm1
  subsd  %xmm0,%xmm1
  movsd  %xmm1,(%rbx)
  cmp    $0x1,%r14d
  je     L136
  mov    %ecx,%eax
  mov    0x8(%rsp),%rdx
  lea    0x8(,%rax,8),%rdi
  lea    0x0(,%r14,8),%rax
  cmp    %rax,%rdi
  setle  %al
  cmp    %r12,%rdx
  setae  %dil
  or     %dil,%al
  je     L166
  lea    0x10(%r13),%rax
  cmp    %rax,%rdx
  setne  %dil
  cmp    $0x2,%r14d
  setne  %al
  test   %al,%dil
  je     L166
  movsd  -0x8(%r12),%xmm2
  mov    %ecx,%edx
  lea    0x8(%r13),%rsi
  xor    %eax,%eax
  shr    %edx
  unpcklpd %xmm2,%xmm2
  shl    $0x4,%rdx
  nopl   0x0(%rax)
L78:
  movupd (%rsi,%rax,1),%xmm1
  movupd 0x8(%rbx,%rax,1),%xmm0
  mulpd  %xmm2,%xmm1
  subpd  %xmm1,%xmm0
  movups %xmm0,0x8(%rbx,%rax,1)
  add    $0x10,%rax
  cmp    %rdx,%rax
  jne    L78
  mov    %ecx,%eax
  or     $0x1,%eax
  test   $0x1,%cl
  je     L136
  cltq
  movsd  -0x8(%r12),%xmm1
  mulsd  0x0(%r13,%rax,8),%xmm1
  lea    (%rbx,%rax,8),%rdx
  movsd  (%rdx),%xmm0
  subsd  %xmm1,%xmm0
  movsd  %xmm0,(%rdx)
L136:
  movsd  -0x1908(%r15),%xmm0
  sub    $0x1908,%r15
  sub    $0x1,%r14
  mov    %ecx,%ebp
  sub    $0x1900,%r13
  sub    $0x8,%r12
  call   <is_zero@plt>
  test   %rax,%rax
  je     L38
L100:
  add    $0x18,%rsp
  mov    $0xffffffff,%eax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  xchg   %ax,%ax
L166:
  lea    -0x2(%rbp),%edx
  mov    $0x1,%eax
  add    $0x2,%rdx
  nopl   0x0(%rax)
L16:
  movsd  0x0(%r13,%rax,8),%xmm1
  mulsd  -0x8(%r12),%xmm1
  movsd  (%rbx,%rax,8),%xmm0
  subsd  %xmm1,%xmm0
  movsd  %xmm0,(%rbx,%rax,8)
  add    $0x1,%rax
  cmp    %rdx,%rax
  jne    L16
  jmp    L136
  nopw   0x0(%rax,%rax,1)
L71:
  test   %ecx,%ecx
  jns    L136
  jmp    L50
```

assistant: ```c
int backrow(int n, double A[][800], double b[], int trans) {
  int i, j;
  if (trans == 0) {
    for (i = n - 1; i >= 0; i--) {
      for (j = i + 1; j < n; j++) {
        b[i] -= A[i][j] * b[j];
      }
      if (is_zero(A[i][i]))
        return -1;
      b[i] /= A[i][i];
    }
  } else {
    for (i = n - 1; i >= 0; i--) {
      if (is_zero(A[i][i]))
        return -1;
      b[i] /= A[i][i];
      for (j = 0; j < i; j++) {
        b[j] -= A[i][j] * b[i];
      }
    }
  }
  return 0;
}
```