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

```asm
<substr>:
  endbr64
  movslq %edx,%r9
  lea    -0x1(%rsi),%eax
  lea    D66(%rip),%r8
  mov    %rdi,%rcx
  lea    (%rax,%r9,1),%edi
  cmp    %eax,%edi
  jle    L155
  mov    %edi,%r11d
  push   %rbp
  mov    %r8,%rdx
  sub    %esi,%r11d
  movslq %esi,%rsi
  push   %rbx
  lea    (%rcx,%rsi,1),%rbx
  sub    %rbx,%rdx
  cmp    $0xe,%rdx
  jbe    L12
  cmp    $0x6,%r11d
  jbe    L12
  lea    0x1(%r11),%r10d
  cmp    $0xe,%r11d
  jbe    L148
  lea    -0x1(%rcx,%rsi,1),%rdx
  mov    %r10d,%ebp
  movdqu (%rdx),%xmm0
  shr    $0x4,%ebp
  movaps %xmm0,D60(%rip)
  cmp    $0x1,%ebp
  je     L120
  movdqu 0x10(%rdx),%xmm1
  movaps %xmm1,D60(%rip)
  cmp    $0x2,%ebp
  je     L120
  movdqu 0x20(%rdx),%xmm2
  movaps %xmm2,D65(%rip)
  cmp    $0x3,%ebp
  je     L120
  movdqu 0x30(%rdx),%xmm3
  movaps %xmm3,D38(%rip)
  cmp    $0x4,%ebp
  je     L120
  movdqu 0x40(%rdx),%xmm4
  movaps %xmm4,D36(%rip)
  cmp    $0x5,%ebp
  je     L120
  movdqu 0x50(%rdx),%xmm5
  movaps %xmm5,D13(%rip)
L120:
  mov    %r10d,%edx
  and    $0xfffffff0,%edx
  mov    %edx,%esi
  add    %edx,%eax
  cmp    %edx,%r10d
  je     L23
  sub    %edx,%r11d
  lea    0x1(%r11),%r10d
  cmp    $0x6,%r11d
  jbe    L95
L72:
  mov    -0x1(%rdx,%rbx,1),%r11
  mov    %r11,(%r8,%rdx,1)
  mov    %r10d,%edx
  and    $0xfffffff8,%edx
  add    %edx,%eax
  add    %edx,%esi
  cmp    %r10d,%edx
  je     L23
L95:
  movslq %eax,%rdx
  movzbl (%rcx,%rdx,1),%r10d
  movslq %esi,%rdx
  mov    %r10b,(%r8,%rdx,1)
  lea    0x1(%rax),%edx
  lea    0x1(%rsi),%r10d
  cmp    %edx,%edi
  jle    L23
  movslq %edx,%rdx
  movslq %r10d,%r10
  movzbl (%rcx,%rdx,1),%edx
  mov    %dl,(%r8,%r10,1)
  lea    0x2(%rax),%edx
  lea    0x2(%rsi),%r10d
  cmp    %edx,%edi
  jle    L23
  movslq %edx,%rdx
  movslq %r10d,%r10
  movzbl (%rcx,%rdx,1),%edx
  mov    %dl,(%r8,%r10,1)
  lea    0x3(%rax),%edx
  lea    0x3(%rsi),%r10d
  cmp    %edx,%edi
  jle    L23
  movslq %edx,%rdx
  movslq %r10d,%r10
  movzbl (%rcx,%rdx,1),%edx
  mov    %dl,(%r8,%r10,1)
  lea    0x4(%rax),%edx
  lea    0x4(%rsi),%r10d
  cmp    %edx,%edi
  jle    L23
  movslq %edx,%rdx
  movslq %r10d,%r10
  movzbl (%rcx,%rdx,1),%edx
  mov    %dl,(%r8,%r10,1)
  lea    0x5(%rax),%edx
  lea    0x5(%rsi),%r10d
  cmp    %edx,%edi
  jle    L23
  movslq %edx,%rdx
  movslq %r10d,%r10
  add    $0x6,%eax
  add    $0x6,%esi
  movzbl (%rcx,%rdx,1),%edx
  mov    %dl,(%r8,%r10,1)
  cmp    %eax,%edi
  jle    L23
  cltq
  movslq %esi,%rsi
  movzbl (%rcx,%rax,1),%eax
  mov    %al,(%r8,%rsi,1)
L23:
  movb   $0x0,(%r8,%r9,1)
  mov    %r8,%rax
  pop    %rbx
  pop    %rbp
  ret
L12:
  mov    %r8,%r10
  cltq
  sub    %rsi,%r10
  nopl   0x0(%rax,%rax,1)
L79:
  movzbl (%rcx,%rax,1),%edx
  mov    %dl,0x1(%r10,%rax,1)
  add    $0x1,%rax
  cmp    %eax,%edi
  jg     L79
  movb   $0x0,(%r8,%r9,1)
  mov    %r8,%rax
  pop    %rbx
  pop    %rbp
  ret
  nopl   0x0(%rax)
L155:
  movb   $0x0,(%r8,%r9,1)
  mov    %r8,%rax
  ret
L148:
  xor    %edx,%edx
  xor    %esi,%esi
  jmp    L72
```

assistant: ```c
char *substr(char *str, int pos, int len) {
  static char str1[100];
  int i, j, end;
  pos--;
  end = pos + len - 1;
  for (i = pos, j = 0; i <= end; i++, j++)
    str1[j] = str[i];
  str1[len] = '\0';
  return str1;
}
```