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

```asm
<merge_sort>:
  endbr64
  cmp    %edx,%esi
  jl     L61
  ret
  nopl   0x0(%rax)
L61:
  mov    %edx,%eax
  push   %r15
  sub    %esi,%eax
  push   %r14
  mov    %rdi,%r14
  push   %r13
  mov    %eax,%r13d
  push   %r12
  sar    %r13d
  mov    %edx,%r12d
  push   %rbp
  add    %esi,%r13d
  mov    %esi,%ebp
  push   %rbx
  sub    $0x18,%rsp
  cmp    %r13d,%esi
  jl     L72
  lea    0x1(%r13),%r15d
  cmp    %r12d,%r15d
  jl     L69
L39:
  add    $0x18,%rsp
  mov    %r12d,%ecx
  mov    %r13d,%edx
  mov    %ebp,%esi
  pop    %rbx
  mov    %r14,%rdi
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  jmp    1050 <merge_array@plt>
  nop
L72:
  mov    %eax,%ebx
  sar    $0x2,%ebx
  add    %esi,%ebx
  cmp    %ebx,%esi
  jl     L109
L86:
  lea    0x1(%rbx),%r15d
  cmp    %r15d,%r13d
  jg     L63
L92:
  mov    %r13d,%ecx
  mov    %ebx,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  call   <merge_array@plt>
  lea    0x1(%r13),%r15d
  cmp    %r12d,%r15d
  jge    L39
L69:
  mov    %r12d,%eax
  sub    %r15d,%eax
  mov    %eax,%ebx
  sar    %ebx
  add    %r15d,%ebx
  cmp    %ebx,%r15d
  jl     L51
L42:
  lea    0x1(%rbx),%r8d
  cmp    %r8d,%r12d
  jg     L74
L66:
  mov    %r12d,%ecx
  mov    %ebx,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <merge_array@plt>
  jmp    L39
  nopl   0x0(%rax)
L109:
  sar    $0x3,%eax
  lea    (%rax,%rsi,1),%r15d
  mov    %r15d,%edx
  call   <merge_sort>
  lea    0x1(%r15),%esi
  mov    %ebx,%edx
  mov    %r14,%rdi
  call   <merge_sort>
  mov    %ebx,%ecx
  mov    %r15d,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  call   <merge_array@plt>
  jmp    L86
  nopl   0x0(%rax)
L74:
  mov    %r12d,%r9d
  mov    %r8d,%esi
  mov    %r14,%rdi
  mov    %r8d,0xc(%rsp)
  sub    %r8d,%r9d
  sar    %r9d
  add    %r8d,%r9d
  mov    %r9d,%edx
  mov    %r9d,0x8(%rsp)
  call   <merge_sort>
  mov    0x8(%rsp),%r9d
  mov    %r12d,%edx
  mov    %r14,%rdi
  lea    0x1(%r9),%esi
  call   <merge_sort>
  mov    0x8(%rsp),%edx
  mov    0xc(%rsp),%esi
  mov    %r12d,%ecx
  mov    %r14,%rdi
  call   <merge_array@plt>
  jmp    L66
L51:
  sar    $0x2,%eax
  mov    %r15d,%esi
  mov    %r14,%rdi
  lea    (%rax,%r15,1),%r8d
  mov    %r8d,%edx
  mov    %r8d,0x8(%rsp)
  call   <merge_sort>
  mov    0x8(%rsp),%r8d
  mov    %ebx,%edx
  mov    %r14,%rdi
  lea    0x1(%r8),%esi
  call   <merge_sort>
  mov    0x8(%rsp),%edx
  mov    %ebx,%ecx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <merge_array@plt>
  jmp    L42
  nopl   0x0(%rax,%rax,1)
L63:
  mov    %r13d,%r8d
  mov    %r15d,%esi
  mov    %r14,%rdi
  sub    %r15d,%r8d
  sar    %r8d
  add    %r15d,%r8d
  mov    %r8d,%edx
  mov    %r8d,0x8(%rsp)
  call   <merge_sort>
  mov    0x8(%rsp),%r8d
  mov    %r13d,%edx
  mov    %r14,%rdi
  lea    0x1(%r8),%esi
  call   <merge_sort>
  mov    0x8(%rsp),%edx
  mov    %r13d,%ecx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <merge_array@plt>
  jmp    L92
```

assistant: ```c
void merge_sort(int a[], int left, int right) {
  if (left < right) {
    int m = left + (right - left) / 2;
    merge_sort(a, left, m);
    merge_sort(a, m + 1, right);
    merge_array(a, left, m, right);
  }
}
```