user: 这段汇编代码用C语言表示是什么样的?

```asm
<str_decode>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x18,%rsp
  mov    %rdi,%r15
  mov    %rsi,%rbx
  mov    %rsi,%rdi
  mov    $0x0,%eax
  call   <ignorestr@plt>
  mov    %eax,0xc(%rsp)
  test   %eax,%eax
  jne    L373
  mov    %eax,%esi
  movzbl (%rbx),%eax
  movzbl %al,%ebp
  mov    %esi,(%rsp)
  mov    %esi,0x4(%rsp)
  mov    %esi,0x8(%rsp)
  test   %ebp,%ebp
  jne    L256
L96:
  movb   $0x0,(%r15)
L117:
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L373:
  mov    %rbx,%rsi
  mov    %r15,%rdi
  call   <strcpy@plt>
  jmp    L117
L342:
  cmp    $0x3d,%ebp
  sete   %dl
  cmpb   $0x3d,0x1(%rbx)
  je     L375
L24:
  cmpl   $0x0,0x4(%rsp)
  je     L260
  cmpl   $0x0,(%rsp)
  je     L183
L260:
  test   %dl,%dl
  jne    L61
L338:
  mov    %al,(%r15)
  mov    %rbx,%rbp
  lea    0x1(%r15),%r15
L314:
  lea    0x1(%rbp),%rbx
  movzbl 0x1(%rbp),%eax
  movzbl %al,%ebp
  test   %ebp,%ebp
  je     L96
L256:
  cmp    $0x3f,%ebp
  je     L342
  cmp    $0xa,%ebp
  je     L57
  cmp    $0x3d,%ebp
  sete   %dl
  cmpl   $0x0,0x8(%rsp)
  je     L24
  test   %dl,%dl
  je     L24
  lea    0x2(%rbx),%rbp
  movzbl 0x2(%rbx),%r12d
  movzbl 0x1(%rbx),%edi
  mov    $0x0,%eax
  call   <qp_code@plt>
  mov    %eax,%ebx
  mov    %r12d,%edi
  mov    $0x0,%eax
  call   <qp_code@plt>
  shl    $0x4,%ebx
  or     %eax,%ebx
  mov    %bl,(%r15)
  lea    0x1(%r15),%r15
  jmp    L314
L375:
  lea    0x1(%rbx),%rbp
  jmp    L314
L57:
  lea    0x1(%rbx),%rbp
  mov    0xc(%rsp),%eax
  mov    %eax,(%rsp)
  mov    %eax,0x4(%rsp)
  mov    %eax,0x8(%rsp)
  jmp    L314
L40:
  add    $0x1,%rbx
  movzbl (%rbx),%ebp
L183:
  mov    %ebp,%edi
  call   <isspace@plt>
  test   %eax,%eax
  jne    L40
  test   %ebp,%ebp
  je     L96
L252:
  add    $0x1,%rbx
  movzbl (%rbx),%r12d
  mov    %r12d,%edi
  call   <isspace@plt>
  test   %eax,%eax
  jne    L252
  test   %r12d,%r12d
  je     L96
L279:
  add    $0x1,%rbx
  movzbl (%rbx),%r13d
  mov    %r13d,%edi
  call   <isspace@plt>
  test   %eax,%eax
  jne    L279
  test   %r13d,%r13d
  je     L96
L318:
  add    $0x1,%rbx
  movzbl (%rbx),%r14d
  mov    %r14d,%edi
  call   <isspace@plt>
  mov    %eax,(%rsp)
  test   %eax,%eax
  jne    L318
  test   %r14d,%r14d
  je     L96
  cmp    $0x3d,%ebp
  je     L151
  cmp    $0x3d,%r12d
  je     L151
  mov    %r12d,%edi
  call   <base64_code@plt>
  mov    %eax,%r12d
  mov    %ebp,%edi
  mov    $0x0,%eax
  call   <base64_code@plt>
  mov    %r12d,%edx
  sar    $0x4,%edx
  and    $0x3,%edx
  shl    $0x2,%eax
  or     %eax,%edx
  mov    %dl,(%r15)
  cmp    $0x3d,%r13d
  jne    L394
  add    $0x1,%r15
  mov    %rbx,%rbp
  movl   $0x1,(%rsp)
  jmp    L314
L394:
  mov    %r13d,%edi
  mov    $0x0,%eax
  call   <base64_code@plt>
  mov    %eax,%ebp
  sar    $0x2,%eax
  and    $0xf,%eax
  shl    $0x4,%r12d
  or     %r12d,%eax
  mov    %al,0x1(%r15)
  cmp    $0x3d,%r14d
  jne    L95
  add    $0x2,%r15
  mov    %rbx,%rbp
  movl   $0x1,(%rsp)
  jmp    L314
L95:
  mov    %r14d,%edi
  mov    $0x0,%eax
  call   <base64_code@plt>
  shl    $0x6,%ebp
  or     %eax,%ebp
  mov    %bpl,0x2(%r15)
  mov    %rbx,%rbp
  lea    0x3(%r15),%r15
  jmp    L314
L61:
  movzbl 0x1(%rbx),%edx
  cmp    $0x3f,%dl
  jne    L338
  lea    0x1(%rbx),%rbp
  mov    0xc(%rsp),%ecx
  mov    %ecx,%esi
  mov    $0x3f,%eax
  jmp    L164
L188:
  add    $0x1,%ecx
  cmp    $0x2,%ecx
  jg     L16
L55:
  add    $0x1,%rbp
  movzbl 0x0(%rbp),%edx
  movzbl %dl,%eax
  test   %eax,%eax
  je     L16
L164:
  cmp    $0x3f,%eax
  je     L188
  or     $0x20,%edx
  movzbl %dl,%edx
  cmp    $0x2,%ecx
  cmove  %edx,%esi
  jmp    L55
L16:
  cmp    $0x71,%esi
  je     L226
  cmp    $0x62,%esi
  mov    $0x1,%eax
  cmovne 0x4(%rsp),%eax
  mov    %eax,0x4(%rsp)
  jmp    L314
L151:
  mov    %rbx,%rbp
  movl   $0x1,(%rsp)
  jmp    L314
L226:
  movl   $0x1,0x8(%rsp)
  jmp    L314
```

assistant: ```c
void str_decode(dst, src) register unsigned char *dst, *src;
{
  register int is_qp, is_base64, is_done;
  register int c1, c2, c3, c4;
  if (ignorestr(src)) {
    strcpy(dst, src);
    return;
  }
  for (is_done = is_qp = is_base64 = 0; (c1 = *src); src++) {
    if (c1 == '?' && src[1] == '=') {
      src++;
      continue;
    } else if (c1 == '\n') {
      src++;
      is_done = is_qp = is_base64 = 0;
      continue;
    } else if (is_qp && c1 == '=') {
      c1 = *++src;
      c2 = *++src;
      *dst++ = (qp_code(c1) << 4) | qp_code(c2);
    } else if (is_base64 && !is_done) {
      while (isspace(c1)) {
        c1 = *++src;
      }
      if (!c1)
        break;
      do {
        c2 = *++src;
      } while (isspace(c2));
      if (!c2)
        break;
      do {
        c3 = *++src;
      } while (isspace(c3));
      if (!c3)
        break;
      do {
        c4 = *++src;
      } while (isspace(c4));
      if (!c4)
        break;
      if (c1 == '=' || c2 == '=') {
        is_done = 1;
        continue;
      }
      c2 = base64_code(c2);
      *dst++ = (base64_code(c1) << 2) | ((c2 & 0x30) >> 4);
      if (c3 == '=')
        is_done = 1;
      else {
        c3 = base64_code(c3);
        *dst++ = ((c2 & 0xF) << 4) | ((c3 & 0x3c) >> 2);
        if (c4 == '=')
          is_done = 1;
        else {
          *dst++ = ((c3 & 0x03) << 6) | base64_code(c4);
        }
      }
    } else if ((c1 == '=') && (src[1] == '?')) {
      c2 = c3 = 0;
      for (;;) {
        c1 = *++src;
        if (c1 == 0)
          break;
        if (c1 != '?') {
          if (c2 == 2)
            c3 = c1 | 0x20;
        } else {
          if (++c2 >= 3)
            break;
        }
      }
      if (c3 == 'q')
        is_qp = 1;
      else if (c3 == 'b')
        is_base64 = 1;
    } else
      *dst++ = c1;
  }
  *dst = '\0';
}
```