user: 请将这段汇编代码片段转换成等效的C代码：

```asm
<hlp_file_randmod>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x28,%rsp
  mov    %rdi,%r13
  mov    %esi,%ebp
  mov    %rdx,%rbx
  mov    %rcx,%r15
  mov    %r8,%r12
  mov    $0x1,%edi
  call   <malloc@plt>
  mov    %rax,(%rsp)
  test   %rax,%rax
  je     L50
  mov    D19(%rip),%rax
  mov    (%rax),%esi
  mov    %r13,%rdi
  call   <open@plt>
  mov    %eax,0xc(%rsp)
  test   %eax,%eax
  js     L19
  mov    D32(%rip),%rax
  mov    (%rax),%edx
  mov    $0x0,%esi
  mov    0xc(%rsp),%edi
  call   <lseek@plt>
  mov    %eax,0x8(%rsp)
  test   %eax,%eax
  js     L178
  mov    $0x0,%eax
  call   <sranddev@plt>
  test   %ebp,%ebp
  je     L107
  mov    %r12,0x10(%rsp)
  mov    %ebp,%eax
  mov    %rax,0x18(%rsp)
  mov    $0xffffffff,%r14d
  mov    $0x0,%r13d
  mov    $0x1,%ebp
  jmp    L111
L50:
  mov    D1(%rip),%rax
  mov    (%rax),%eax
L68:
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L19:
  mov    (%rsp),%rdi
  call   <free@plt>
  mov    D1(%rip),%rax
  mov    (%rax),%eax
  jmp    L68
L178:
  mov    (%rsp),%rdi
  call   <free@plt>
  mov    0xc(%rsp),%edi
  call   <close@plt>
  mov    D1(%rip),%rax
  mov    (%rax),%eax
  jmp    L68
L187:
  mov    %edx,%ecx
  mov    %ebp,%edx
  mov    (%rsp),%rsi
  mov    0xc(%rsp),%edi
  call   <pread@plt>
  cmp    $0x1,%eax
  jne    L53
  mov    (%rsp),%rax
  movzbl (%rax),%eax
  mov    %al,(%r15,%r13,1)
  mov    0x10(%rsp),%rdi
  mov    %rdi,%r12
  mov    %al,(%rdi)
  cmp    (%r15,%r13,1),%al
  jne    L147
L132:
  mov    $0x0,%eax
  call   <rand@plt>
  cltd
  shr    $0x18,%edx
  add    %edx,%eax
  movzbl %al,%eax
  sub    %edx,%eax
  mov    %al,(%r12)
  cmp    (%r15,%r13,1),%al
  je     L132
L147:
  mov    (%rbx,%r13,4),%ecx
  mov    %ebp,%edx
  mov    %r12,%rsi
  mov    0xc(%rsp),%edi
  call   <pwrite@plt>
  cmp    $0x1,%eax
  jne    L157
  add    $0x1,%r13
  addq   $0x1,0x10(%rsp)
  add    $0x1,%r14d
  cmp    0x18(%rsp),%r13
  je     L107
L111:
  mov    %r13d,%r12d
L92:
  mov    $0x0,%eax
  call   <rand@plt>
  cltd
  idivl  0x8(%rsp)
  mov    %edx,(%rbx,%r13,4)
  cmp    %r14d,%r13d
  jb     L187
  mov    %r14d,%eax
  mov    $0x0,%ecx
L35:
  mov    %eax,%esi
  cmp    (%rbx,%rsi,4),%edx
  cmove  %ebp,%ecx
  sub    $0x1,%eax
  cmp    %eax,%r12d
  jae    L35
  test   %ecx,%ecx
  jne    L92
  jmp    L187
L53:
  mov    0xc(%rsp),%edi
  call   <close@plt>
  mov    (%rsp),%rdi
  call   <free@plt>
  mov    D1(%rip),%rax
  mov    (%rax),%eax
  jmp    L68
L157:
  mov    0xc(%rsp),%edi
  call   <close@plt>
  mov    (%rsp),%rdi
  call   <free@plt>
  mov    D1(%rip),%rax
  mov    (%rax),%eax
  jmp    L68
L107:
  mov    0xc(%rsp),%edi
  call   <close@plt>
  mov    (%rsp),%rdi
  call   <free@plt>
  mov    $0x0,%eax
  jmp    L68
```

assistant: ```c
int hlp_file_randmod(const char *path, unsigned int mod_amount, off_t *positions, unsigned char *orig_chars, unsigned char *mod_chars) {
  off_t filesize;
  int fd;
  unsigned int i, j, flag;
  void *buf = NULL;
  buf = malloc(1);
  if (NULL == buf)
    return errno;
  fd = open(path, O_RDWR);
  if (fd < 0) {
    free(buf);
    return errno;
  }
  filesize = lseek(fd, 0, SEEK_END);
  if (filesize < 0) {
    free(buf);
    close(fd);
    return errno;
  }
  sranddev();
  for (i = 0; i < mod_amount; i++) {
    flag = 1;
    while (flag) {
      positions[i] = (rand() % filesize);
      flag = 0;
      for (j = i - 1; j <= i; j--)
        if (positions[j] == positions[i])
          flag = 1;
    }
    if (1 != pread(fd, buf, 1, positions[i])) {
      close(fd);
      free(buf);
      return errno;
    }
    orig_chars[i] = (*(unsigned char *)buf);
    mod_chars[i] = orig_chars[i];
    while (mod_chars[i] == orig_chars[i])
      mod_chars[i] = (unsigned char)(rand() % 256);
    if (1 != pwrite(fd, &(mod_chars[i]), 1, positions[i])) {
      close(fd);
      free(buf);
      return errno;
    }
  }
  close(fd);
  free(buf);
  return 0;
}
```