user: Demonstrate the C code that generates the assembly output below:

```asm
<mergesort_parall>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  mov    %edx,%r13d
  push   %r12
  sub    %esi,%r13d
  push   %rbp
  push   %rbx
  sub    $0x28,%rsp
  cmp    $0x1,%r13d
  jle    L129
  mov    %r13d,%r9d
  mov    %rdi,%r14
  mov    %esi,%ebp
  mov    %edx,%r12d
  sar    %r9d
  mov    %ecx,%ebx
  lea    (%r9,%rsi,1),%r15d
  cmp    $0x1,%ecx
  jle    L200
  mov    %ecx,%eax
  sar    %eax
  mov    %eax,0x8(%rsp)
  cmp    $0x1,%r9d
  je     L156
  mov    %r13d,%r11d
  sar    $0x2,%r11d
  lea    (%rsi,%r11,1),%r10d
  cmp    $0x1,%eax
  je     L125
  mov    %ecx,%eax
  sar    $0x2,%eax
  mov    %eax,0xc(%rsp)
  cmp    $0x1,%r11d
  je     L60
  sar    $0x3,%r13d
  add    %esi,%r13d
  cmp    $0x1,%eax
  je     L207
  mov    %ecx,%esi
  mov    %r13d,%edx
  mov    %r11d,0x18(%rsp)
  sar    $0x3,%esi
  mov    %r9d,0x14(%rsp)
  mov    %esi,%ecx
  mov    %esi,0x10(%rsp)
  mov    %ebp,%esi
  mov    %r10d,0x1c(%rsp)
  call   <mergesort_parall>
  mov    0x1c(%rsp),%r10d
  mov    %r13d,%esi
  mov    %r14,%rdi
  mov    0x10(%rsp),%eax
  mov    0xc(%rsp),%ecx
  mov    %r10d,%edx
  mov    %r10d,0x10(%rsp)
  sub    %eax,%ecx
  call   <mergesort_parall>
  mov    0x10(%rsp),%r10d
  mov    0x14(%rsp),%r9d
  mov    0x18(%rsp),%r11d
L167:
  mov    %r10d,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  mov    %r11d,0x18(%rsp)
  mov    %r9d,0x14(%rsp)
  mov    %r10d,0x10(%rsp)
  call   <merge@plt>
  mov    0x18(%rsp),%r11d
  mov    0x14(%rsp),%r9d
  mov    0x10(%rsp),%r10d
L60:
  sub    %r11d,%r9d
  cmp    $0x1,%r9d
  jle    L176
  mov    0x8(%rsp),%eax
  sar    %r9d
  sub    0xc(%rsp),%eax
  lea    (%r9,%r10,1),%r13d
  cmp    $0x1,%eax
  jle    L9
  mov    %eax,%r8d
  mov    %r10d,%esi
  mov    %r13d,%edx
  mov    %r14,%rdi
  sar    %r8d
  mov    %r10d,0xc(%rsp)
  mov    %r8d,%ecx
  mov    %eax,0x14(%rsp)
  mov    %r8d,0x10(%rsp)
  call   <mergesort_parall>
  mov    0x14(%rsp),%eax
  mov    %r15d,%edx
  mov    %r13d,%esi
  mov    0x10(%rsp),%r8d
  mov    %r14,%rdi
  sub    %r8d,%eax
  mov    %eax,%ecx
  call   <mergesort_parall>
  mov    0xc(%rsp),%r10d
L38:
  mov    %r15d,%edx
  mov    %r10d,%esi
  mov    %r14,%rdi
  call   <merge@plt>
L176:
  mov    %r15d,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  call   <merge@plt>
L156:
  mov    %r12d,%eax
  sub    %r15d,%eax
  cmp    $0x1,%eax
  jle    L151
  mov    %eax,%edx
  sub    0x8(%rsp),%ebx
  sar    %edx
  lea    (%r15,%rdx,1),%r13d
  cmp    $0x1,%ebx
  jle    L118
  mov    %ebx,%ecx
  sar    %ecx
  mov    %ecx,0x8(%rsp)
  cmp    $0x1,%edx
  je     L138
  sar    $0x2,%eax
  lea    (%rax,%r15,1),%r8d
  cmp    $0x1,%ecx
  je     L84
  mov    %ebx,%eax
  mov    %r8d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  sar    $0x2,%eax
  mov    %r8d,0xc(%rsp)
  mov    %eax,%ecx
  mov    %eax,0x10(%rsp)
  call   <mergesort_parall>
  mov    0x8(%rsp),%ecx
  mov    0x10(%rsp),%eax
  mov    %r13d,%edx
  mov    0xc(%rsp),%esi
  mov    %r14,%rdi
  sub    %eax,%ecx
  call   <mergesort_parall>
L127:
  mov    %r13d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <merge@plt>
L138:
  mov    %r12d,%eax
  sub    %r13d,%eax
  cmp    $0x1,%eax
  jle    L140
  sar    %eax
  sub    0x8(%rsp),%ebx
  lea    (%rax,%r13,1),%r8d
  cmp    $0x1,%ebx
  jle    L113
  mov    %ebx,%eax
  mov    %r8d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  sar    %eax
  mov    %r8d,0x8(%rsp)
  mov    %eax,%ecx
  mov    %eax,0xc(%rsp)
  call   <mergesort_parall>
  mov    0xc(%rsp),%eax
  mov    0x8(%rsp),%esi
  mov    %r12d,%edx
  mov    %r14,%rdi
  sub    %eax,%ebx
  mov    %ebx,%ecx
  call   <mergesort_parall>
L153:
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <merge@plt>
L140:
  mov    %r12d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <merge@plt>
  jmp    L151
L200:
  mov    %r15d,%edx
  call   <mergesort_seq@plt>
  mov    %r12d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
L151:
  add    $0x28,%rsp
  mov    %r12d,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  jmp    1060 <merge@plt>
  nopl   0x0(%rax)
L129:
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopw   0x0(%rax,%rax,1)
L118:
  mov    %r13d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  mov    %r12d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  jmp    L140
  xchg   %ax,%ax
L125:
  mov    %r10d,%edx
  mov    %r10d,0xc(%rsp)
  call   <mergesort_seq@plt>
  mov    0xc(%rsp),%esi
  mov    %r15d,%edx
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  jmp    L176
  nopl   0x0(%rax)
L113:
  mov    %r8d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  mov    %r8d,0x8(%rsp)
  call   <mergesort_seq@plt>
  mov    0x8(%rsp),%esi
  mov    %r12d,%edx
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  jmp    L153
  nop
L84:
  mov    %r8d,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  mov    %r8d,0xc(%rsp)
  call   <mergesort_seq@plt>
  mov    0xc(%rsp),%esi
  mov    %r13d,%edx
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  jmp    L127
  nopw   0x0(%rax,%rax,1)
L207:
  mov    %r13d,%edx
  mov    %r10d,0x10(%rsp)
  mov    %r11d,0x18(%rsp)
  mov    %r9d,0x14(%rsp)
  call   <mergesort_seq@plt>
  mov    0x10(%rsp),%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  mov    0x18(%rsp),%r11d
  mov    0x14(%rsp),%r9d
  mov    0x10(%rsp),%r10d
  jmp    L167
  nopw   0x0(%rax,%rax,1)
L9:
  mov    %r10d,%esi
  mov    %r13d,%edx
  mov    %r14,%rdi
  mov    %r10d,0xc(%rsp)
  call   <mergesort_seq@plt>
  mov    %r15d,%edx
  mov    %r13d,%esi
  mov    %r14,%rdi
  call   <mergesort_seq@plt>
  mov    0xc(%rsp),%r10d
  jmp    L38
```

assistant: ```c
void mergesort_parall(int *v, int a, int b, int threads) {
  if (b - a <= 1)
    return;
  int m = a + (b - a) / 2;
  if (threads > 1) {
#pragma omp parallel sections
    {
#pragma omp section
      mergesort_parall(v, a, m, threads / 2);
#pragma omp section
      mergesort_parall(v, m, b, threads - threads / 2);
    }
  } else {
    mergesort_seq(v, a, m);
    mergesort_seq(v, m, b);
  }
  merge(v, a, b);
}
```