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

```asm
<square_step>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x38,%rsp
  mov    %rdi,%r14
  mov    %edx,%edi
  mov    %ecx,%r15d
  mov    %edx,%eax
  sub    %ecx,%eax
  cltq
  lea    (%r14,%rax,8),%rbx
  mov    (%rbx),%rdx
  mov    %esi,%eax
  sub    %ecx,%eax
  movslq %eax,%r10
  mov    %esi,0x28(%rsp)
  movslq %esi,%r8
  mov    %edi,0x10(%rsp)
  movslq %edi,%r9
  lea    (%r14,%r9,8),%r13
  lea    (%r14,%r8,8),%r12
  mov    %r8,(%rsp)
  mov    (%rdx,%r8,4),%eax
  add    (%rdx,%r10,4),%eax
  mov    0x0(%r13),%rdx
  mov    %r10,0x18(%rsp)
  add    (%rdx,%r10,4),%eax
  mov    (%r12),%rdx
  mov    %r9,0x8(%rsp)
  add    (%rdx,%r9,4),%eax
  lea    0x3(%rax),%edx
  cmovs  %edx,%eax
  mov    %eax,%ebp
  sar    $0x2,%ebp
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    %r15d,%eax
  shr    $0x1f,%eax
  mov    %r15d,%esi
  add    %r15d,%eax
  sar    %eax
  neg    %eax
  mov    %eax,%edi
  add    0x10(%rsp),%eax
  cltq
  lea    (%r14,%rax,8),%r15
  mov    %edi,0x14(%rsp)
  mov    %edi,%eax
  mov    0x28(%rsp),%ecx
  add    %ecx,%eax
  movslq %eax,%r11
  mov    (%r15),%rax
  add    %edx,%ebp
  mov    %r11,0x20(%rsp)
  mov    %ebp,(%rax,%r11,4)
  mov    (%rbx),%rdx
  mov    %esi,0x28(%rsp)
  mov    %esi,%ebp
  mov    %ecx,%ebx
  add    %ecx,%ebp
  movslq %ebp,%rbp
  mov    (%rdx,%rbp,4),%eax
  mov    (%rsp),%r8
  add    (%rdx,%r8,4),%eax
  mov    0x0(%r13),%rdx
  add    (%rdx,%rbp,4),%eax
  mov    (%r12),%rdx
  mov    0x8(%rsp),%r9
  add    (%rdx,%r9,4),%eax
  lea    0x3(%rax),%edx
  cmovs  %edx,%eax
  mov    %eax,%ecx
  sar    $0x2,%ecx
  mov    %ecx,0x2c(%rsp)
  mov    $0x0,%eax
  call   <salt@plt>
  sub    0x14(%rsp),%ebx
  movslq %ebx,%rbx
  mov    (%r15),%rdx
  add    0x2c(%rsp),%eax
  mov    %eax,(%rdx,%rbx,4)
  mov    0x28(%rsp),%eax
  add    0x10(%rsp),%eax
  cltq
  lea    (%r14,%rax,8),%r15
  mov    (%r15),%rdx
  mov    0x0(%r13),%rcx
  mov    0x18(%rsp),%r10
  mov    (%rdx,%r10,4),%eax
  add    (%rcx,%r10,4),%eax
  mov    (%rsp),%r8
  add    (%rdx,%r8,4),%eax
  mov    (%r12),%rdx
  mov    0x8(%rsp),%r9
  add    (%rdx,%r9,4),%eax
  lea    0x3(%rax),%edx
  cmovs  %edx,%eax
  mov    %eax,%esi
  sar    $0x2,%esi
  mov    %esi,0x28(%rsp)
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%ecx
  mov    0x10(%rsp),%eax
  sub    0x14(%rsp),%eax
  cltq
  lea    (%r14,%rax,8),%r14
  mov    (%r14),%rdx
  mov    0x28(%rsp),%esi
  lea    (%rsi,%rcx,1),%eax
  mov    0x20(%rsp),%r11
  mov    %eax,(%rdx,%r11,4)
  mov    (%r15),%rdx
  mov    0x0(%r13),%rcx
  mov    (%rsp),%r8
  mov    (%rdx,%r8,4),%eax
  add    (%rcx,%rbp,4),%eax
  add    (%rdx,%rbp,4),%eax
  mov    (%r12),%rdx
  mov    0x8(%rsp),%r9
  add    (%rdx,%r9,4),%eax
  lea    0x3(%rax),%ebp
  cmovns %eax,%ebp
  sar    $0x2,%ebp
  mov    $0x0,%eax
  call   <salt@plt>
  mov    %eax,%edx
  mov    (%r14),%rax
  add    %edx,%ebp
  mov    %ebp,(%rax,%rbx,4)
  add    $0x38,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  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();
}
```