user: 请将这段汇编代码片段转换成等效的C代码:

```asm
<square_step>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %rbx
  sub    $0x28,%rsp
  mov    %rdi,-0x18(%rbp)
  mov    %esi,-0x1c(%rbp)
  mov    %edx,-0x20(%rbp)
  mov    %ecx,-0x24(%rbp)
  mov    -0x20(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%edx
  mov    -0x20(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x1c(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  mov    (%rax),%eax
  lea    (%rdx,%rax,1),%ecx
  mov    -0x20(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %eax,%ecx
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x20(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %ecx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  mov    %eax,%ebx
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    -0x24(%rbp),%eax
  mov    %eax,%ecx
  shr    $0x1f,%ecx
  add    %ecx,%eax
  sar    %eax
  neg    %eax
  mov    %eax,%ecx
  mov    -0x20(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x24(%rbp),%eax
  mov    %eax,%esi
  shr    $0x1f,%esi
  add    %esi,%eax
  sar    %eax
  neg    %eax
  mov    %eax,%esi
  mov    -0x1c(%rbp),%eax
  add    %esi,%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  add    %ebx,%edx
  mov    %edx,(%rax)
  mov    -0x20(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%edx
  mov    -0x20(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x1c(%rbp),%esi
  mov    -0x24(%rbp),%eax
  add    %esi,%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  mov    (%rax),%eax
  lea    (%rdx,%rax,1),%esi
  mov    -0x20(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%ecx
  mov    -0x24(%rbp),%eax
  add    %ecx,%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  lea    (%rsi,%rax,1),%ecx
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x20(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %ecx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  mov    %eax,%ebx
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    -0x24(%rbp),%eax
  mov    %eax,%ecx
  shr    $0x1f,%ecx
  add    %ecx,%eax
  sar    %eax
  neg    %eax
  mov    %eax,%ecx
  mov    -0x20(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x24(%rbp),%eax
  mov    %eax,%esi
  shr    $0x1f,%esi
  add    %esi,%eax
  sar    %eax
  mov    %eax,%esi
  mov    -0x1c(%rbp),%eax
  add    %esi,%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  add    %ebx,%edx
  mov    %edx,(%rax)
  mov    -0x20(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%edx
  mov    -0x20(%rbp),%ecx
  mov    -0x24(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x1c(%rbp),%eax
  sub    -0x24(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  mov    (%rax),%eax
  lea    (%rdx,%rax,1),%ecx
  mov    -0x20(%rbp),%edx
  mov    -0x24(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %eax,%ecx
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x20(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %ecx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  mov    %eax,%ebx
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    -0x24(%rbp),%eax
  mov    %eax,%ecx
  shr    $0x1f,%ecx
  add    %ecx,%eax
  sar    %eax
  mov    %eax,%ecx
  mov    -0x20(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x24(%rbp),%eax
  mov    %eax,%esi
  shr    $0x1f,%esi
  add    %esi,%eax
  sar    %eax
  neg    %eax
  mov    %eax,%esi
  mov    -0x1c(%rbp),%eax
  add    %esi,%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  add    %ebx,%edx
  mov    %edx,(%rax)
  mov    -0x20(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%ecx
  mov    -0x24(%rbp),%eax
  add    %ecx,%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%edx
  mov    -0x20(%rbp),%ecx
  mov    -0x24(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x1c(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  mov    (%rax),%eax
  lea    (%rdx,%rax,1),%esi
  mov    -0x20(%rbp),%edx
  mov    -0x24(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x1c(%rbp),%ecx
  mov    -0x24(%rbp),%eax
  add    %ecx,%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  lea    (%rsi,%rax,1),%ecx
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdx
  mov    -0x20(%rbp),%eax
  cltq
  shl    $0x2,%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  add    %ecx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  mov    %eax,%ebx
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    -0x24(%rbp),%eax
  mov    %eax,%ecx
  shr    $0x1f,%ecx
  add    %ecx,%eax
  sar    %eax
  mov    %eax,%ecx
  mov    -0x20(%rbp),%eax
  add    %ecx,%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x18(%rbp),%rax
  add    %rcx,%rax
  mov    (%rax),%rcx
  mov    -0x24(%rbp),%eax
  mov    %eax,%esi
  shr    $0x1f,%esi
  add    %esi,%eax
  sar    %eax
  mov    %eax,%esi
  mov    -0x1c(%rbp),%eax
  add    %esi,%eax
  cltq
  shl    $0x2,%rax
  add    %rcx,%rax
  add    %ebx,%edx
  mov    %edx,(%rax)
  nop
  mov    -0x8(%rbp),%rbx
  leave
  ret
```

assistant: ```c
void square_step(int **map, int x, int y, int length) {
  map[y - length / 2][x - length / 2] = (map[y - length][x - length] + map[y - length][x] + map[y][x - length] + map[x][y]) / 4 + salt();
  map[y - length / 2][x + length / 2] = (map[y - length][x] + map[y - length][x + length] + map[y][x + length] + map[x][y]) / 4 + salt();
  map[y + length / 2][x - length / 2] = (map[y][x - length] + map[y + length][x - length] + map[y + length][x] + map[x][y]) / 4 + salt();
  map[y + length / 2][x + length / 2] = (map[y][x + length] + map[y + length][x] + map[y + length][x + length] + map[x][y]) / 4 + salt();
}
```