user: 请将这段汇编代码片段转换成等效的C代码：

```asm
<concatenation>:
  endbr64
  push   %r13
  push   %r12
  mov    %rdi,%r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  sub    $0x8,%rsp
  call   <strlen@plt>
  mov    %rbp,%rdi
  mov    %eax,%ebx
  call   <strlen@plt>
  lea    (%rbx,%rax,1),%edi
  mov    %eax,%r13d
  call   <malloc@plt>
  mov    %rax,%r8
  test   %ebx,%ebx
  jle    L250
  lea    0x1(%r12),%rsi
  mov    %r8,%rdx
  lea    -0x1(%rbx),%eax
  mov    %ebx,%ecx
  sub    %rsi,%rdx
  cmp    $0xe,%rdx
  jbe    L189
  cmp    $0x6,%eax
  jbe    L189
  cmp    $0xe,%eax
  jbe    L74
  mov    %ebx,%edx
  xor    %eax,%eax
  shr    $0x4,%edx
  shl    $0x4,%rdx
L25:
  movdqu (%r12,%rax,1),%xmm0
  movups %xmm0,(%r8,%rax,1)
  add    $0x10,%rax
  cmp    %rdx,%rax
  jne    L25
  mov    %ebx,%edx
  and    $0xfffffff0,%edx
  mov    %edx,%eax
  cmp    %edx,%ebx
  je     L250
  mov    %ebx,%ecx
  sub    %edx,%ecx
  lea    -0x1(%rcx),%esi
  cmp    $0x6,%esi
  jbe    L66
L202:
  mov    (%r12,%rdx,1),%rsi
  mov    %rsi,(%r8,%rdx,1)
  mov    %ecx,%edx
  and    $0xfffffff8,%edx
  add    %edx,%eax
  cmp    %edx,%ecx
  je     L250
L66:
  movslq %eax,%rdx
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  lea    0x1(%rax),%edx
  cmp    %edx,%ebx
  jle    L250
  movslq %edx,%rdx
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  lea    0x2(%rax),%edx
  cmp    %edx,%ebx
  jle    L250
  movslq %edx,%rdx
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  lea    0x3(%rax),%edx
  cmp    %edx,%ebx
  jle    L250
  movslq %edx,%rdx
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  lea    0x4(%rax),%edx
  cmp    %edx,%ebx
  jle    L250
  movslq %edx,%rdx
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  lea    0x5(%rax),%edx
  cmp    %edx,%ebx
  jle    L250
  movslq %edx,%rdx
  add    $0x6,%eax
  movzbl (%r12,%rdx,1),%ecx
  mov    %cl,(%r8,%rdx,1)
  cmp    %eax,%ebx
  jle    L250
  cltq
  movzbl (%r12,%rax,1),%edx
  mov    %dl,(%r8,%rax,1)
L250:
  test   %r13d,%r13d
  jle    L173
  movslq %ebx,%rdx
  lea    0x1(%rbp),%rdi
  lea    -0x1(%r13),%eax
  mov    %r13d,%esi
  add    %r8,%rdx
  mov    %rdx,%rcx
  sub    %rdi,%rcx
  cmp    $0xe,%rcx
  jbe    L321
  cmp    $0x6,%eax
  jbe    L321
  cmp    $0xe,%eax
  jbe    L128
  mov    %r13d,%ecx
  xor    %eax,%eax
  shr    $0x4,%ecx
  shl    $0x4,%rcx
  nopw   0x0(%rax,%rax,1)
L147:
  movdqu 0x0(%rbp,%rax,1),%xmm1
  movups %xmm1,(%rdx,%rax,1)
  add    $0x10,%rax
  cmp    %rcx,%rax
  jne    L147
  mov    %r13d,%ecx
  and    $0xfffffff0,%ecx
  mov    %ecx,%eax
  cmp    %ecx,%r13d
  je     L173
  mov    %r13d,%esi
  sub    %ecx,%esi
  lea    -0x1(%rsi),%edi
  cmp    $0x6,%edi
  jbe    L11
L263:
  mov    0x0(%rbp,%rcx,1),%rdi
  mov    %rdi,(%rdx,%rcx,1)
  mov    %esi,%edx
  and    $0xfffffff8,%edx
  add    %edx,%eax
  cmp    %edx,%esi
  je     L173
L11:
  movslq %eax,%rdx
  movzbl 0x0(%rbp,%rdx,1),%ecx
  lea    (%rbx,%rax,1),%edx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  lea    0x1(%rax),%edx
  cmp    %edx,%r13d
  jle    L173
  movslq %edx,%rcx
  add    %ebx,%edx
  movzbl 0x0(%rbp,%rcx,1),%ecx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  lea    0x2(%rax),%edx
  cmp    %r13d,%edx
  jge    L173
  movslq %edx,%rcx
  add    %ebx,%edx
  movzbl 0x0(%rbp,%rcx,1),%ecx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  lea    0x3(%rax),%edx
  cmp    %edx,%r13d
  jle    L173
  movslq %edx,%rcx
  add    %ebx,%edx
  movzbl 0x0(%rbp,%rcx,1),%ecx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  lea    0x4(%rax),%edx
  cmp    %edx,%r13d
  jle    L173
  movslq %edx,%rcx
  add    %ebx,%edx
  movzbl 0x0(%rbp,%rcx,1),%ecx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  lea    0x5(%rax),%edx
  cmp    %edx,%r13d
  jle    L173
  movslq %edx,%rcx
  add    %ebx,%edx
  add    $0x6,%eax
  movzbl 0x0(%rbp,%rcx,1),%ecx
  movslq %edx,%rdx
  mov    %cl,(%r8,%rdx,1)
  cmp    %eax,%r13d
  jle    L173
  movslq %eax,%rdx
  add    %eax,%ebx
  movzbl 0x0(%rbp,%rdx,1),%edx
  movslq %ebx,%rbx
  mov    %dl,(%r8,%rbx,1)
L173:
  add    $0x8,%rsp
  mov    %r8,%rax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nopl   0x0(%rax,%rax,1)
L321:
  mov    %r13d,%r13d
  xor    %eax,%eax
  nopl   (%rax)
L97:
  movzbl 0x0(%rbp,%rax,1),%ecx
  mov    %cl,(%rdx,%rax,1)
  add    $0x1,%rax
  cmp    %r13,%rax
  jne    L97
  add    $0x8,%rsp
  mov    %r8,%rax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nop
L189:
  mov    %ebx,%ecx
  xor    %eax,%eax
  nopl   0x0(%rax)
L168:
  movzbl (%r12,%rax,1),%edx
  mov    %dl,(%r8,%rax,1)
  add    $0x1,%rax
  cmp    %rcx,%rax
  jne    L168
  jmp    L250
L74:
  xor    %edx,%edx
  xor    %eax,%eax
  jmp    L202
L128:
  xor    %ecx,%ecx
  xor    %eax,%eax
  jmp    L263
```

assistant: ```c
char *concatenation(char *ch1, char *ch2) {
  int size1 = strlen(ch1);
  int size2 = strlen(ch2);
  char *concat = malloc((size1 + size2) * sizeof(char));
  int i = 0;
  for (i = 0; i < size1; i++) {
    concat[i] = ch1[i];
  }
  for (i = 0; i < size2; i++) {
    concat[size1 + i] = ch2[i];
  }
  return concat;
}
```