user: 下面的汇编指令对应的C源代码是什么：

```asm
<decode_quoted_printable>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x18,%rsp
  mov    %ecx,0x8(%rsp)
  mov    (%rdx),%r14d
  movl   $0x0,(%rdx)
  mov    $0x0,%eax
  test   %esi,%esi
  je     L71
  mov    %rdi,%rbx
  mov    %esi,%ebp
  mov    %rdx,%r15
  lea    0x1(%rsi),%r13d
  mov    %r13d,%edi
  call   <malloc@plt>
  mov    %rax,%r12
  test   %rax,%rax
  je     L117
  cmpl   $0x0,0x8(%rsp)
  je     L4
  lea    -0x1(%rbp),%edx
  mov    %rax,%rdi
  mov    $0x0,%ecx
  mov    $0x20,%r10d
  movabs $0x7e0000007e03ff,%r13
  jmp    L469
L358:
  movzbl 0x1(%rbx),%r9d
  mov    %r9d,%esi
  and    $0xffffffdf,%esi
  sub    $0x41,%esi
  cmp    $0x5,%sil
  jbe    L86
  lea    -0x30(%r9),%esi
  cmp    $0x9,%sil
  jbe    L86
L319:
  lea    0x1(%rdi),%rsi
  mov    %al,(%rdi)
  add    $0x1,%ecx
  cmp    %ecx,%r14d
  jbe    L493
  lea    -0x1(%rdx),%eax
  test   %edx,%edx
  je     L493
  mov    %rsi,%rdi
  mov    %edx,%ebp
  mov    %eax,%edx
  mov    %r8,%rbx
L469:
  lea    0x1(%rbx),%r8
  movzbl (%rbx),%eax
  cmp    $0x3d,%al
  je     L358
  cmp    $0x5f,%al
  cmove  %r10d,%eax
  jmp    L319
L86:
  movzbl 0x2(%rbx),%esi
  lea    -0x30(%rsi),%r11d
  cmp    $0x36,%r11b
  ja     L319
  bt     %r11,%r13
  jae    L319
  movzbl %r9b,%eax
  mov    $0x30,%r8d
  cmp    $0x39,%r9b
  jbe    L250
  cmp    $0x47,%r9b
  sbb    %r8d,%r8d
  and    $0xffffffe0,%r8d
  add    $0x57,%r8d
L250:
  sub    %r8d,%eax
  shl    $0x4,%eax
  mov    $0x30,%r8d
  cmp    $0x39,%sil
  jbe    L96
  cmp    $0x47,%sil
  sbb    %r8d,%r8d
  and    $0xffffffe0,%r8d
  add    $0x57,%r8d
L96:
  sub    %r8d,%esi
  or     %esi,%eax
  test   %edx,%edx
  je     L223
  cmp    $0x2,%ebp
  je     L294
  lea    -0x3(%rbp),%edx
L223:
  lea    0x3(%rbx),%r8
  jmp    L319
L294:
  mov    $0x0,%edx
  jmp    L223
L493:
  movb   $0x0,(%rsi)
  sub    %r12,%rsi
  mov    %esi,(%r15)
  add    $0x1,%esi
  mov    %r12,%rdi
  call   <realloc@plt>
L71:
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L4:
  mov    %r13d,%edi
  call   <malloc@plt>
  mov    %rax,0x8(%rsp)
  test   %rax,%rax
  je     L150
  mov    %ebp,%edx
  mov    %rbx,%rsi
  mov    0x8(%rsp),%rbx
  mov    %rbx,%rdi
  call   <memcpy@plt>
  mov    %ebp,%ebp
  movb   $0x0,(%rbx,%rbp,1)
  mov    %r12,%r13
  jmp    L224
L150:
  mov    %r12,%rdi
  call   <free@plt>
  mov    $0x0,%eax
  jmp    L71
L121:
  mov    %rbx,%rdi
  call   <strlen@plt>
  cltq
  lea    -0x1(%rbx,%rax,1),%rdx
  mov    $0x0,%edi
L5:
  cmp    %rbx,%rdx
  jae    L512
  jmp    L179
L231:
  sub    $0x1,%rdx
  cmp    %rbx,%rdx
  jb     L179
L512:
  movzbl (%rdx),%eax
  cmp    $0x9,%al
  je     L231
  cmp    $0x20,%al
  je     L231
L179:
  movb   $0x0,0x1(%rdx)
  mov    %r13,%rdx
  mov    %r14d,%r9d
  jmp    L205
L252:
  test   %rdi,%rdi
  je     L505
  lea    0x1(%rdx),%r13
  movb   $0xa,(%rdx)
  mov    %r13,%rbp
  sub    %r12,%rbp
  mov    %r14d,%eax
  cmp    %rax,%rbp
  jge    L157
L405:
  test   %rdi,%rdi
  je     L434
  mov    %rdi,%rbx
L224:
  mov    $0xa,%esi
  mov    %rbx,%rdi
  call   <strchr@plt>
  test   %rax,%rax
  je     L121
  lea    0x1(%rax),%rdi
  lea    -0x1(%rax),%rdx
  cmp    %rbx,%rdx
  jb     L179
  cmpb   $0xd,-0x1(%rax)
  jne    L512
  lea    -0x2(%rax),%rdx
  jmp    L5
L46:
  movzbl 0x1(%rbx),%eax
  test   %al,%al
  je     L461
  movzbl 0x2(%rbx),%esi
  mov    %eax,%r8d
  and    $0xffffffdf,%r8d
  sub    $0x41,%r8d
  cmp    $0x5,%r8b
  jbe    L341
  lea    -0x30(%rax),%r8d
  cmp    $0x9,%r8b
  jbe    L341
L116:
  movb   $0x3d,(%rdx)
  mov    %rcx,%rbx
  lea    0x1(%rdx),%rdx
L497:
  mov    %rdx,%rbp
  sub    %r12,%rbp
  cmp    %r9,%rbp
  jge    L446
L205:
  lea    0x1(%rbx),%rcx
  movzbl (%rbx),%eax
  test   %al,%al
  je     L252
  cmp    $0x3d,%al
  je     L46
  mov    %al,(%rdx)
  mov    %rcx,%rbx
  lea    0x1(%rdx),%rdx
  jmp    L497
L341:
  lea    -0x30(%rsi),%r8d
  cmp    $0x36,%r8b
  ja     L116
  movabs $0x7e0000007e03ff,%r11
  bt     %r8,%r11
  jae    L116
  movzbl %al,%ecx
  mov    $0x30,%r8d
  cmp    $0x39,%al
  jbe    L112
  cmp    $0x47,%al
  sbb    %r8d,%r8d
  and    $0xffffffe0,%r8d
  add    $0x57,%r8d
L112:
  mov    %ecx,%eax
  sub    %r8d,%eax
  shl    $0x4,%eax
  mov    $0x30,%ecx
  cmp    $0x39,%sil
  jbe    L170
  cmp    $0x47,%sil
  sbb    %ecx,%ecx
  and    $0xffffffe0,%ecx
  add    $0x57,%ecx
L170:
  sub    %ecx,%esi
  or     %eax,%esi
  mov    %sil,(%rdx)
  add    $0x3,%rbx
  lea    0x1(%rdx),%rdx
  jmp    L497
L434:
  mov    %r13,%rdx
  jmp    L446
L157:
  mov    %r13,%rdx
  jmp    L446
L117:
  mov    $0x0,%eax
  jmp    L71
L505:
  mov    %rdx,%rbp
  sub    %r12,%rbp
  jmp    L446
L461:
  mov    %rdx,%rbp
  sub    %r12,%rbp
  mov    %r14d,%eax
  cmp    %rax,%rbp
  jl     L408
L446:
  movb   $0x0,(%rdx)
  mov    0x8(%rsp),%rdi
  call   <free@plt>
  mov    %ebp,(%r15)
  lea    0x1(%rbp),%esi
  mov    %r12,%rdi
  call   <realloc@plt>
  jmp    L71
L408:
  mov    %rdx,%r13
  jmp    L405
```

assistant: ```c
char *decode_quoted_printable(unsigned char *buf, unsigned int len, unsigned int *ret_len, int header) {
  unsigned char *dest, *deststart;
  unsigned int limit = *ret_len;
  *ret_len = 0;
  if (!len)
    return NULL;
  if (!(dest = (unsigned char *)malloc(len + 1)))
    return NULL;
  deststart = dest;
  if (header) {
    unsigned int real_len = 0;
    while (len--) {
      unsigned char c = *buf++;
      if ('=' == c) {
        unsigned char c2;
        c = buf[0];
        c2 = buf[1];
        if (((((c) >= '0') && ((c) <= '9')) || (((c) >= 'A') && ((c) <= 'F')) || (((c) >= 'a') && ((c) <= 'f'))) && ((((c2) >= '0') && ((c2) <= '9')) || (((c2) >= 'A') && ((c2) <= 'F')) || (((c2) >= 'a') && ((c2) <= 'f')))) {
          c = (((c) - (((c) > '9') ? (((c) > 'F') ? 'a' - 10 : 'A' - 10) : '0')) << 4) | ((c2) - (((c2) > '9') ? (((c2) > 'F') ? 'a' - 10 : 'A' - 10) : '0'));
          if (len)
            len--;
          if (len)
            len--;
          buf += 2;
        } else
          c = '=';
      } else if ('_' == c)
        c = ' ';
      *dest++ = c;
      if (++real_len >= limit)
        break;
    }
    *dest = 0;
    *ret_len = dest - deststart;
    return (char *)realloc(deststart, *ret_len + 1);
  } else {
    unsigned char *text, *textstart;
    if (!(text = (unsigned char *)malloc(len + 1))) {
      free(dest);
      return NULL;
    }
    memcpy(text, buf, len);
    text[len] = 0;
    textstart = text;
    while (text) {
      unsigned char c;
      unsigned char *lp = text;
      {
        unsigned char *ep;
        if ((ep = (unsigned char *)strchr((char *)lp, '\n'))) {
          text = ep + 1;
          ep--;
          if (ep >= lp) {
            if ('\r' == *ep)
              ep--;
          }
        } else {
          ep = lp + strlen((char *)lp) - 1;
          text = NULL;
        }
        while ((ep >= lp) && (((c = *ep) == ' ') || (c == '\t')))
          ep--;
        *(ep + 1) = '\0';
      }
      do {
        switch (c = *lp++) {
        case '\0':
          if (text)
            *dest++ = '\n';
          break;
        case '=':
          if ((c = *lp)) {
            unsigned char d = *(lp + 1);
            if (((((c) >= '0') && ((c) <= '9')) || (((c) >= 'A') && ((c) <= 'F')) || (((c) >= 'a') && ((c) <= 'f'))) && ((((d) >= '0') && ((d) <= '9')) || (((d) >= 'A') && ((d) <= 'F')) || (((d) >= 'a') && ((d) <= 'f')))) {
              *dest++ = (((c) - (((c) > '9') ? (((c) > 'F') ? 'a' - 10 : 'A' - 10) : '0')) << 4) | ((d) - (((d) > '9') ? (((d) > 'F') ? 'a' - 10 : 'A' - 10) : '0'));
              lp += 2;
            } else {
              *dest++ = '=';
            }
          }
          break;
        default:
          *dest++ = c;
          break;
        }
        if ((dest - deststart) >= limit) {
          text = NULL;
          break;
        }
      } while (c);
    }
    *dest = 0;
    free(textstart);
    *ret_len = dest - deststart;
    return (char *)realloc(deststart, *ret_len + 1);
  }
}
```