user: 请将以下的汇编代码转换成C语言代码：

```asm
<expand>:
  endbr64
  push   %r15
  xor    %r15d,%r15d
  push   %r14
  push   %r13
  mov    %rdi,%r13
  push   %r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  mov    %rdi,%rbx
  sub    $0x18,%rsp
  xchg   %ax,%ax
L113:
  movsbl 0x0(%r13),%edi
  mov    %r13,%r14
  mov    %r15d,%r12d
  add    $0x1,%r13
  add    $0x1,%r15d
  call   <isspace@plt>
  test   %rax,%rax
  jne    L113
  cmpb   $0x2d,(%r14)
  jne    L100
  movslq %r12d,%rax
  mov    %r15d,%edx
  lea    0x1(%rbx,%rax,1),%rax
  sub    %eax,%edx
  nopl   0x0(%rax)
L45:
  lea    (%rdx,%rax,1),%ecx
  mov    %rax,%r14
  add    $0x1,%rax
  cmpb   $0x2d,-0x1(%rax)
  mov    %ecx,0xc(%rsp)
  je     L45
L121:
  mov    %rbx,%rdi
  call   <strlen@plt>
  lea    -0x1(%rax),%edx
  movslq %edx,%r12
  nopw   0x0(%rax,%rax,1)
L78:
  movsbl (%rbx,%r12,1),%edi
  mov    %r12d,%r13d
  lea    (%rbx,%r12,1),%r15
  call   <isspace@plt>
  mov    %rax,%r8
  mov    %r12,%rax
  sub    $0x1,%r12
  test   %r8,%r8
  jne    L78
  cmpb   $0x2d,(%r15)
  jne    L98
  sub    $0x1,%r13d
  movslq %r13d,%r13
  nopl   (%rax)
L25:
  mov    %r13,%rax
  sub    $0x1,%r13
  cmpb   $0x2d,0x1(%rbx,%r13,1)
  je     L25
L98:
  mov    0xc(%rsp),%r15d
  movb   $0x0,0x1(%rbx,%rax,1)
  movzbl (%r14),%r13d
  add    $0x1,%r15d
  movslq %r15d,%r12
  add    %rbx,%r12
  movsbl (%r12),%edi
  test   %dil,%dil
  je     L89
  xor    %r14d,%r14d
  jmp    L16
  nopw   0x0(%rax,%rax,1)
L178:
  call   <isalnum@plt>
  test   %rax,%rax
  je     L67
  movslq %r14d,%rax
  add    $0x1,%r15d
  add    $0x1,%r14d
  mov    %r13b,0x0(%rbp,%rax,1)
  movzbl (%r12),%r13d
  movslq %r15d,%r12
  add    %rbx,%r12
  movsbl (%r12),%edi
  test   %dil,%dil
  je     L131
L16:
  cmp    $0x2d,%dil
  jne    L178
  lea    0x1(%r15),%r12d
  movslq %r12d,%r12
  add    %rbx,%r12
  movsbl (%r12),%edi
  call   <isalnum@plt>
  test   %rax,%rax
  je     L67
  movzbl (%r12),%eax
  cmp    %r13b,%al
  jle    L158
  lea    0x1(%r14),%eax
  mov    %r13d,%edx
  cltq
  nopl   (%rax)
L74:
  mov    %dl,-0x1(%rbp,%rax,1)
  movzbl (%r12),%r13d
  add    $0x1,%edx
  mov    %eax,%r14d
  add    $0x1,%rax
  cmp    %dl,%r13b
  jg     L74
  add    $0x2,%r15d
L168:
  movslq %r15d,%r12
  add    %rbx,%r12
  movsbl (%r12),%edi
  test   %dil,%dil
  jne    L16
  nopl   0x0(%rax)
L131:
  movslq %r14d,%rax
  add    $0x1,%r14d
  add    %rbp,%rax
  movslq %r14d,%r14
L90:
  mov    %r13b,(%rax)
  xor    %eax,%eax
  movb   $0x0,0x0(%rbp,%r14,1)
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nop
L67:
  add    $0x18,%rsp
  mov    $0xffffffff,%eax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   0x0(%rax)
L158:
  mov    %eax,%r13d
  add    $0x2,%r15d
  jmp    L168
L100:
  mov    %r12d,0xc(%rsp)
  jmp    L121
L89:
  mov    %rbp,%rax
  mov    $0x1,%r14d
  jmp    L90
```

assistant: ```c
int expand(char s1[], char s2[]) {
  int i, j;
  char ch;
  i = 0;
  while (isspace(s1[i])) {
    i++;
  }
  while (s1[i] == '-') {
    i++;
  }
  int len = strlen(s1) - 1;
  while (isspace(s1[len])) {
    len--;
  }
  while (s1[len] == '-') {
    len--;
  }
  s1[len + 1] = '\0';
  j = 0;
  char start = s1[i++];
  while (s1[i] != '\0') {
    if (s1[i] == '-') {
      i++;
      if (isalnum(s1[i])) {
        for (ch = start; ch < s1[i]; ch++) {
          s2[j++] = ch;
        }
        start = s1[i++];
      } else {
        return -1;
      }
    } else if (isalnum(s1[i])) {
      s2[j++] = start;
      start = s1[i++];
    } else {
      return -1;
    }
  }
  s2[j++] = start;
  s2[j] = '\0';
  return 0;
}
```