user: 提供的汇编代码用C语言表示会是什么样子：

```asm
<subtraction>:
  endbr64
  push   %r15
  mov    %rdi,%r15
  push   %r14
  push   %r13
  mov    %rdx,%r13
  push   %r12
  mov    %rcx,%r12
  push   %rbp
  mov    %esi,%ebp
  mov    $0xa,%esi
  push   %rbx
  sub    $0x28,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x18(%rsp)
  xor    %eax,%eax
  lea    0xe(%rsp),%rbx
  mov    %rbx,%rdi
  call   <bzero@plt>
  mov    $0x8,%esi
  mov    %r12,%rdi
  call   <bzero@plt>
  test   %ebp,%ebp
  js     L315
  movslq %ebp,%r14
  mov    %r15,%rsi
  mov    %rbx,%rdi
  lea    0x1(%r14),%rdx
  call   <memcpy@plt>
  mov    %rbx,%rdx
  mov    $0x1,%eax
  jmp    L249
L300:
  sub    %edi,%ecx
  mov    %cl,-0x1(%r12,%rax,1)
  cmp    %eax,%ebp
  jl     L396
L144:
  add    $0x1,%rax
  add    $0x1,%rdx
L249:
  movzbl (%rdx),%ecx
  movzbl -0x1(%r13,%rax,1),%edi
  mov    %eax,%esi
  cmp    %dil,%cl
  jae    L300
  cmp    %eax,%ebp
  jl     L396
  movzbl 0x1(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x1(%rax),%esi
  movb   $0xff,0x1(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x2(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x2(%rax),%esi
  movb   $0xff,0x2(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x3(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x3(%rax),%esi
  movb   $0xff,0x3(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x4(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x4(%rax),%esi
  movb   $0xff,0x4(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x5(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x5(%rax),%esi
  movb   $0xff,0x5(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x6(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x6(%rax),%esi
  movb   $0xff,0x6(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x7(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x7(%rax),%esi
  movb   $0xff,0x7(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x8(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  lea    0x8(%rax),%esi
  movb   $0xff,0x8(%rdx)
  cmp    %esi,%ebp
  jl     L144
  movzbl 0x9(%rdx),%ecx
  test   %cl,%cl
  jne    L387
  movb   $0xff,0x9(%rdx)
  jmp    L144
  nopl   0x0(%rax)
L387:
  sub    $0x1,%ecx
  movslq %esi,%rsi
  mov    %cl,0xe(%rsp,%rsi,1)
  movzbl (%rdx),%ecx
  sub    %edi,%ecx
  mov    %cl,-0x1(%r12,%rax,1)
  jmp    L144
  nopl   0x0(%rax)
L396:
  cmpb   $0x0,(%r12,%r14,1)
  jne    L315
  lea    -0x1(%rbp),%eax
  test   %ebp,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x2(%rbp),%eax
  cmp    $0x1,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x3(%rbp),%eax
  cmp    $0x2,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x4(%rbp),%eax
  cmp    $0x3,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x5(%rbp),%eax
  cmp    $0x4,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x6(%rbp),%eax
  cmp    $0x5,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x7(%rbp),%eax
  cmp    $0x6,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  lea    -0x8(%rbp),%eax
  cmp    $0x7,%ebp
  je     L22
  movslq %eax,%rdx
  cmpb   $0x0,(%r12,%rdx,1)
  jne    L22
  mov    $0xffffffff,%eax
  cmp    $0x9,%ebp
  jne    L22
  cmpb   $0x1,(%r12)
  sbb    %eax,%eax
L22:
  mov    0x18(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L283
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L315:
  mov    %ebp,%eax
  jmp    L22
L283:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
int subtraction(unsigned char *a, int a_len, unsigned char *b, unsigned char *subres) {
  int i, j, k;
  unsigned char diversion[10];
  bzero(diversion, sizeof(diversion));
  bzero(subres, sizeof(subres));
  for (i = 0; i <= a_len; i++)
    diversion[i] = a[i];
  for (i = 0; i <= a_len; i++) {
    if (diversion[i] >= b[i])
      subres[i] = diversion[i] - b[i];
    else {
      j = i + 1;
      while (j <= a_len) {
        if (diversion[j] > 0) {
          diversion[j]--;
          subres[i] = 256 - b[i] + diversion[i];
          break;
        } else
          diversion[j] = 255;
        j++;
      }
    }
  }
  for (j = a_len; j >= 0; j--) {
    if (subres[j] > 0)
      break;
    a_len--;
  }
  return a_len;
}
```