user: 提供的汇编代码用C语言表示会是什么样子：

```asm
<decode_quantum>:
  endbr64
  mov    %rsi,%rcx
  movsbl (%rsi),%esi
  mov    %rdi,%rdx
  lea    -0x41(%rsi),%eax
  cmp    $0x19,%al
  jbe    L28
  cmp    $0x39,%sil
  jg     L404
  cmp    $0x2f,%sil
  jg     L319
  mov    $0x3e,%eax
  cmp    $0x2b,%sil
  je     L337
  xor    %eax,%eax
  cmp    $0x2f,%sil
  mov    $0x3f,%esi
  cmove  %esi,%eax
L337:
  movsbl 0x1(%rcx),%esi
  lea    -0x41(%rsi),%edi
  cmp    $0x19,%dil
  jbe    L227
L419:
  cmp    $0x39,%sil
  jg     L89
  cmp    $0x2f,%sil
  jg     L201
  cmp    $0x2b,%sil
  je     L116
  cmp    $0x2f,%sil
  jne    L196
  shl    $0x6,%eax
  add    $0x3f,%eax
L196:
  movsbl 0x2(%rcx),%esi
  lea    -0x41(%rsi),%edi
  cmp    $0x19,%dil
  jbe    L204
L207:
  cmp    $0x39,%sil
  jg     L198
  cmp    $0x2f,%sil
  jg     L252
  cmp    $0x2b,%sil
  je     L83
  cmp    $0x2f,%sil
  jne    L317
  shl    $0x6,%eax
  add    $0x3f,%eax
  nopl   0x0(%rax,%rax,1)
L317:
  movsbl 0x3(%rcx),%ecx
  lea    -0x41(%rcx),%esi
  cmp    $0x19,%sil
  ja     L29
L171:
  shl    $0x6,%eax
  lea    -0x41(%rax,%rcx,1),%eax
L206:
  mov    %eax,%ecx
  shr    $0x10,%eax
  rol    $0x8,%cx
  mov    %al,(%rdx)
  mov    %cx,0x1(%rdx)
  ret
  nopl   0x0(%rax)
L89:
  cmp    $0x3d,%sil
  je     L281
  lea    -0x61(%rsi),%edi
  cmp    $0x19,%dil
  ja     L196
  shl    $0x6,%eax
  lea    -0x47(%rax,%rsi,1),%eax
  movsbl 0x2(%rcx),%esi
  lea    -0x41(%rsi),%edi
  cmp    $0x19,%dil
  ja     L207
L204:
  movsbl 0x3(%rcx),%ecx
  shl    $0x6,%eax
  lea    -0x41(%rax,%rsi,1),%eax
  lea    -0x41(%rcx),%esi
  cmp    $0x19,%sil
  jbe    L171
L29:
  cmp    $0x39,%cl
  jg     L34
  cmp    $0x2f,%cl
  jg     L213
  cmp    $0x2b,%cl
  je     L169
  cmp    $0x2f,%cl
  jne    L206
  shl    $0x6,%eax
  add    $0x3f,%eax
  jmp    L206
  nop
L198:
  cmp    $0x3d,%sil
  je     L103
  lea    -0x61(%rsi),%edi
  cmp    $0x19,%dil
  ja     L317
  shl    $0x6,%eax
  lea    -0x47(%rax,%rsi,1),%eax
  jmp    L317
  nopl   0x0(%rax,%rax,1)
L404:
  lea    -0x61(%rsi),%eax
  sub    $0x47,%esi
  cmp    $0x1a,%al
  mov    $0x0,%eax
  cmovb  %esi,%eax
  movsbl 0x1(%rcx),%esi
  lea    -0x41(%rsi),%edi
  cmp    $0x19,%dil
  ja     L419
L227:
  shl    $0x6,%eax
  lea    -0x41(%rax,%rsi,1),%eax
  jmp    L196
  nopl   (%rax)
L28:
  lea    -0x41(%rsi),%eax
  jmp    L337
L34:
  cmp    $0x3d,%cl
  je     L279
  lea    -0x61(%rcx),%esi
  cmp    $0x19,%sil
  ja     L206
  shl    $0x6,%eax
  lea    -0x47(%rax,%rcx,1),%eax
  mov    %eax,%ecx
  shr    $0x10,%eax
  rol    $0x8,%cx
  mov    %al,(%rdx)
  mov    %cx,0x1(%rdx)
  ret
  nopl   (%rax)
L103:
  shl    $0x6,%eax
  jmp    L317
  nopl   0x0(%rax,%rax,1)
L116:
  shl    $0x6,%eax
  add    $0x3e,%eax
  jmp    L196
  nopl   0x0(%rax,%rax,1)
L281:
  shl    $0x6,%eax
  jmp    L196
  nopl   0x0(%rax,%rax,1)
L83:
  shl    $0x6,%eax
  add    $0x3e,%eax
  jmp    L317
  nopl   0x0(%rax,%rax,1)
L319:
  add    $0x4,%esi
  movsbl %sil,%eax
  jmp    L337
  nopl   0x0(%rax)
L201:
  add    $0x4,%esi
  shl    $0x6,%eax
  movsbl %sil,%esi
  add    %esi,%eax
  jmp    L196
  nopl   0x0(%rax)
L252:
  add    $0x4,%esi
  shl    $0x6,%eax
  movsbl %sil,%esi
  add    %esi,%eax
  jmp    L317
  nopl   0x0(%rax)
L279:
  shl    $0x6,%eax
  jmp    L206
  nopl   0x0(%rax,%rax,1)
L169:
  shl    $0x6,%eax
  add    $0x3e,%eax
  jmp    L206
  nopl   0x0(%rax,%rax,1)
L213:
  add    $0x4,%ecx
  shl    $0x6,%eax
  movsbl %cl,%ecx
  add    %ecx,%eax
  jmp    L206
```

assistant: ```c
void decode_quantum(unsigned char *dest, const char *src) {
  unsigned int x = 0;
  int i;
  for (i = 0; i < 4; i++) {
    if (src[i] >= 'A' && src[i] <= 'Z')
      x = (x << 6) + (unsigned int)(src[i] - 'A' + 0);
    else if (src[i] >= 'a' && src[i] <= 'z')
      x = (x << 6) + (unsigned int)(src[i] - 'a' + 26);
    else if (src[i] >= '0' && src[i] <= '9')
      x = (x << 6) + (unsigned int)(src[i] - '0' + 52);
    else if (src[i] == '+')
      x = (x << 6) + 62;
    else if (src[i] == '/')
      x = (x << 6) + 63;
    else if (src[i] == '=')
      x = (x << 6);
  }
  dest[2] = (unsigned char)(x & 255);
  x >>= 8;
  dest[1] = (unsigned char)(x & 255);
  x >>= 8;
  dest[0] = (unsigned char)(x & 255);
}
```