user: What would the C source look like for the assembly code provided here:

```asm
<update_r>:
  endbr64
  push   %r15
  mov    %ecx,%r15d
  mov    %r8d,%ecx
  push   %r14
  push   %r13
  mov    %edx,%r13d
  mov    %esi,%edx
  push   %r12
  mov    %esi,%r12d
  mov    %edi,%esi
  push   %rbp
  mov    %edi,%ebp
  xor    %edi,%edi
  push   %rbx
  mov    %r8d,%ebx
  mov    %ebx,%r14d
  neg    %r14d
  sub    $0x28,%rsp
  call   <update@plt>
  mov    %r15d,0xc(%rsp)
  add    $0x1,%r15d
  mov    %ebp,%esi
  mov    %r14d,%ecx
  mov    %r15d,%edx
  xor    %edi,%edi
  call   <update@plt>
  mov    %r13d,0x14(%rsp)
  add    $0x1,%r13d
  xor    %edi,%edi
  mov    %r14d,%ecx
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    $0x1,%r14d
  call   <update@plt>
  mov    %ebx,%ecx
  mov    %r15d,%edx
  mov    %r13d,%esi
  xor    %edi,%edi
  call   <update@plt>
  mov    %r14d,%r10d
  mov    %r12d,%edx
  mov    %ebp,%esi
  sub    %r12d,%r10d
  mov    $0x1,%edi
  imul   %ebx,%r10d
  mov    %r10d,%ecx
  mov    %r10d,0x1c(%rsp)
  call   <update@plt>
  mov    0xc(%rsp),%r11d
  mov    %r15d,%edx
  mov    %ebp,%esi
  mov    $0x1,%edi
  imul   %ebx,%r11d
  mov    %r11d,%ecx
  mov    %r11d,0x18(%rsp)
  call   <update@plt>
  mov    0x1c(%rsp),%r10d
  mov    %r12d,%edx
  mov    %r13d,%esi
  lea    -0x1(%r12),%eax
  mov    $0x1,%edi
  neg    %r10d
  mov    %eax,0x10(%rsp)
  mov    %r10d,%ecx
  call   <update@plt>
  mov    0x18(%rsp),%ecx
  mov    %r15d,%edx
  mov    %r13d,%esi
  mov    $0x1,%edi
  neg    %ecx
  call   <update@plt>
  mov    %r14d,%ecx
  mov    %r12d,%edx
  mov    %ebp,%esi
  sub    %ebp,%ecx
  mov    $0x2,%edi
  lea    -0x1(%rbp),%r14d
  imul   %ebx,%ecx
  mov    %ecx,0x18(%rsp)
  call   <update@plt>
  mov    0x18(%rsp),%ecx
  mov    %r15d,%edx
  mov    %ebp,%esi
  mov    $0x2,%edi
  neg    %ecx
  call   <update@plt>
  mov    0x14(%rsp),%ecx
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    $0x2,%edi
  imul   %ebx,%ecx
  mov    %ecx,0x18(%rsp)
  call   <update@plt>
  mov    0x18(%rsp),%ecx
  mov    %r15d,%edx
  mov    %r13d,%esi
  mov    $0x2,%edi
  neg    %ecx
  call   <update@plt>
  mov    0x10(%rsp),%ecx
  mov    %r12d,%edx
  mov    %ebp,%esi
  mov    $0x3,%edi
  imul   %r14d,%ecx
  imul   %ebx,%ecx
  call   <update@plt>
  mov    0xc(%rsp),%ecx
  mov    %r15d,%edx
  mov    %ebp,%esi
  mov    $0x3,%edi
  neg    %ecx
  imul   %r14d,%ecx
  imul   %ebx,%ecx
  call   <update@plt>
  mov    0x14(%rsp),%r14d
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    0x10(%rsp),%ecx
  mov    $0x3,%edi
  mov    %r14d,%eax
  neg    %eax
  imul   %eax,%ecx
  imul   %ebx,%ecx
  call   <update@plt>
  mov    0xc(%rsp),%ecx
  add    $0x28,%rsp
  mov    %r15d,%edx
  mov    %r13d,%esi
  mov    $0x3,%edi
  imul   %r14d,%ecx
  imul   %ebx,%ecx
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  jmp    1050 <update@plt>
```

assistant: ```c
void update_r(int x1, int y1, int x2, int y2, int val) {
  update(0, x1, y1, val);
  update(0, x1, y2 + 1, -val);
  update(0, x2 + 1, y1, -val);
  update(0, x2 + 1, y2 + 1, val);
  update(1, x1, y1, val * (1 - y1));
  update(1, x1, y2 + 1, val * y2);
  update(1, x2 + 1, y1, val * (y1 - 1));
  update(1, x2 + 1, y2 + 1, -val * y2);
  update(2, x1, y1, val * (1 - x1));
  update(2, x1, y2 + 1, (x1 - 1) * val);
  update(2, x2 + 1, y1, val * x2);
  update(2, x2 + 1, y2 + 1, -x2 * val);
  update(3, x1, y1, (x1 - 1) * (y1 - 1) * val);
  update(3, x1, y2 + 1, -y2 * (x1 - 1) * val);
  update(3, x2 + 1, y1, -x2 * (y1 - 1) * val);
  update(3, x2 + 1, y2 + 1, x2 * y2 * val);
}
```