user: 请从给定的汇编指令推导出C源代码:

```asm
<fnMergeSort>:
  endbr64
  cmp    %edx,%esi
  jl     L126
  ret
  nopl   0x0(%rax)
L126:
  lea    (%rsi,%rdx,1),%eax
  push   %r15
  push   %r14
  mov    %rdi,%r14
  push   %r13
  mov    %eax,%r13d
  push   %r12
  shr    $0x1f,%r13d
  mov    %edx,%r12d
  push   %rbp
  add    %eax,%r13d
  mov    %esi,%ebp
  push   %rbx
  sar    %r13d
  sub    $0x18,%rsp
  cmp    %r13d,%esi
  jl     L86
  lea    0x1(%r13),%r15d
  cmp    %r12d,%r15d
  jl     L82
L26:
  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 <fnMerge@plt>
  nopw   0x0(%rax,%rax,1)
L86:
  lea    (%rsi,%r13,1),%eax
  mov    %eax,%r15d
  shr    $0x1f,%r15d
  add    %eax,%r15d
  sar    %r15d
  cmp    %r15d,%esi
  jl     L21
L67:
  lea    0x1(%r15),%ebx
  cmp    %ebx,%r13d
  jg     L105
L120:
  mov    %r15d,%edx
  mov    %r13d,%ecx
  mov    %ebp,%esi
  mov    %r14,%rdi
  call   <fnMerge@plt>
  lea    0x1(%r13),%r15d
  cmp    %r12d,%r15d
  jge    L26
L82:
  lea    (%r15,%r12,1),%eax
  mov    %eax,%ebx
  shr    $0x1f,%ebx
  add    %eax,%ebx
  sar    %ebx
  cmp    %ebx,%r15d
  jl     L20
L111:
  lea    0x1(%rbx),%r8d
  cmp    %r8d,%r12d
  jg     L107
L13:
  mov    %r12d,%ecx
  mov    %ebx,%edx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <fnMerge@plt>
  jmp    L26
  nopl   0x0(%rax,%rax,1)
L21:
  lea    (%rsi,%r15,1),%eax
  mov    %eax,%ebx
  shr    $0x1f,%ebx
  add    %eax,%ebx
  sar    %ebx
  mov    %ebx,%edx
  call   <fnMergeSort>
  lea    0x1(%rbx),%esi
  mov    %r15d,%edx
  mov    %r14,%rdi
  call   <fnMergeSort>
  mov    %r15d,%ecx
  mov    %ebx,%edx
  mov    %ebp,%esi
  mov    %r14,%rdi
  call   <fnMerge@plt>
  jmp    L67
  cs nopw 0x0(%rax,%rax,1)
L107:
  lea    (%r12,%r8,1),%eax
  mov    %r8d,%esi
  mov    %r14,%rdi
  mov    %r8d,0xc(%rsp)
  mov    %eax,%r9d
  shr    $0x1f,%r9d
  add    %eax,%r9d
  sar    %r9d
  mov    %r9d,%edx
  mov    %r9d,0x8(%rsp)
  call   <fnMergeSort>
  mov    0x8(%rsp),%r9d
  mov    %r12d,%edx
  mov    %r14,%rdi
  lea    0x1(%r9),%esi
  call   <fnMergeSort>
  mov    0x8(%rsp),%edx
  mov    0xc(%rsp),%esi
  mov    %r12d,%ecx
  mov    %r14,%rdi
  call   <fnMerge@plt>
  jmp    L13
  nopl   (%rax)
L20:
  lea    (%r15,%rbx,1),%eax
  mov    %r15d,%esi
  mov    %r14,%rdi
  mov    %eax,%r8d
  shr    $0x1f,%r8d
  add    %eax,%r8d
  sar    %r8d
  mov    %r8d,%edx
  mov    %r8d,0x8(%rsp)
  call   <fnMergeSort>
  mov    0x8(%rsp),%r8d
  mov    %ebx,%edx
  mov    %r14,%rdi
  lea    0x1(%r8),%esi
  call   <fnMergeSort>
  mov    0x8(%rsp),%edx
  mov    %ebx,%ecx
  mov    %r15d,%esi
  mov    %r14,%rdi
  call   <fnMerge@plt>
  jmp    L111
  nopl   (%rax)
L105:
  lea    0x0(%r13,%rbx,1),%eax
  mov    %ebx,%esi
  mov    %r14,%rdi
  mov    %eax,%r8d
  shr    $0x1f,%r8d
  add    %eax,%r8d
  sar    %r8d
  mov    %r8d,%edx
  mov    %r8d,0x8(%rsp)
  call   <fnMergeSort>
  mov    0x8(%rsp),%r8d
  mov    %r13d,%edx
  mov    %r14,%rdi
  lea    0x1(%r8),%esi
  call   <fnMergeSort>
  mov    0x8(%rsp),%edx
  mov    %r13d,%ecx
  mov    %ebx,%esi
  mov    %r14,%rdi
  call   <fnMerge@plt>
  jmp    L120
```

assistant: ```c
void fnMergeSort(int a[], int low, int high) {
  int mid;
  if (low < high) {
    mid = (low + high) / 2;
    fnMergeSort(a, low, mid);
    fnMergeSort(a, mid + 1, high);
    fnMerge(a, low, mid, high);
  }
}
```