user: 下面的汇编指令对应的C源代码是什么：

```asm
<uudecode>:
  endbr64
  push   %r15
  mov    %rdi,%r8
  push   %r14
  mov    %rdx,%r14
  push   %r13
  push   %r12
  push   %rbp
  mov    %rcx,%rbp
  push   %rbx
  sub    $0x38,%rsp
  mov    %rsi,0x10(%rsp)
  mov    %fs:0x28,%rax
  mov    %rax,0x28(%rsp)
  xor    %eax,%eax
  test   %rcx,%rcx
  jne    L62
  mov    %rdi,(%rsp)
  mov    %rdx,%rdi
  call   <strlen@plt>
  mov    (%rsp),%r8
  mov    %rax,%rbp
L62:
  lea    0x24(%rsp),%r12
  mov    $0x1,%ecx
  xor    %r15d,%r15d
  xor    %ebx,%ebx
  sub    %r12d,%ecx
  mov    %ecx,%r13d
  nopl   (%rax)
L101:
  cmp    %r15,0x10(%rsp)
  seta   %al
L45:
  cmp    %rbp,%rbx
  jae    L18
  test   %al,%al
  je     L18
  add    $0x1,%rbx
  movzbl -0x1(%r14,%rbx,1),%edx
  cmp    $0x1f,%dl
  jle    L45
  lea    -0x20(%rdx),%eax
  and    $0x3f,%eax
  mov    %rax,0x18(%rsp)
  sete   %al
  cmp    %rbp,%rbx
  setae  %dl
  or     %dl,%al
  jne    L18
  xor    %r9d,%r9d
  nopw   0x0(%rax,%rax,1)
L175:
  xor    %esi,%esi
  mov    $0x4,%edx
  mov    %r12,%rdi
  mov    %r8,0x8(%rsp)
  mov    %r9,(%rsp)
  call   <memset@plt>
  cmp    %rbx,%rbp
  mov    (%rsp),%r9
  mov    0x8(%rsp),%r8
  jbe    L140
  mov    %r12,%rax
L115:
  add    $0x1,%rbx
  movzbl -0x1(%r14,%rbx,1),%edx
  cmp    $0x1f,%dl
  jbe    L218
  sub    $0x20,%edx
L218:
  lea    0x0(%r13,%rax,1),%esi
  cmp    %rbp,%rbx
  mov    %dl,(%rax)
  setb   %dl
  cmp    $0x3,%esi
  setbe  %sil
  add    $0x1,%rax
  test   %dl,%sil
  jne    L115
L108:
  movzbl 0x25(%rsp),%r10d
  movzbl 0x24(%rsp),%esi
  add    $0x3,%r9
  mov    %r10d,%eax
  shl    $0x2,%esi
  sar    $0x4,%eax
  shl    $0x4,%r10d
  and    $0x3,%eax
  or     %esi,%eax
  movzbl 0x26(%rsp),%esi
  mov    %al,(%r8,%r15,1)
  mov    %esi,%eax
  shl    $0x6,%esi
  sar    $0x2,%eax
  and    $0xf,%eax
  or     %r10d,%eax
  mov    %al,0x1(%r8,%r15,1)
  movzbl 0x27(%rsp),%eax
  add    $0x3,%r15
  and    $0x3f,%eax
  or     %esi,%eax
  cmp    %r9,0x18(%rsp)
  seta   %sil
  cmp    %r15,0x10(%rsp)
  mov    %al,-0x1(%r8,%r15,1)
  seta   %al
  test   %al,%sil
  je     L195
  test   %dl,%dl
  jne    L175
L195:
  cmp    %rbx,%rbp
  ja     L43
  jmp    L101
  nopl   0x0(%rax)
L116:
  add    $0x1,%rbx
  cmp    %rbp,%rbx
  jae    L101
L43:
  movzbl (%r14,%rbx,1),%eax
  cmp    $0x20,%al
  jg     L116
  cmp    %rbx,%rbp
  ja     L61
  jmp    L101
  nopl   0x0(%rax,%rax,1)
L134:
  cmp    $0x20,%al
  jg     L101
  add    $0x1,%rbx
  cmp    %rbp,%rbx
  je     L101
  movzbl (%r14,%rbx,1),%eax
L61:
  test   %al,%al
  jne    L134
  jmp    L101
  nopl   0x0(%rax,%rax,1)
L140:
  xor    %edx,%edx
  jmp    L108
L18:
  mov    %r15d,%eax
  mov    0x28(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L31
  add    $0x38,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L31:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
int uudecode(char *target, size_t tlen, const char *source, size_t slen) {
  int i;
  char ch;
  size_t rd = 0;
  size_t wr = 0;
  size_t block;
  size_t len;
  unsigned char cell[4];
  if (slen == 0)
    slen = strlen(source);
  while (rd < slen && wr < tlen) {
    ch = source[rd++];
    if (ch < ' ')
      continue;
    len = (ch - ' ') & 0x3f;
    if (len <= 0 || rd >= slen)
      break;
    block = 0;
    while (block < len && wr < tlen && rd < slen) {
      memset(cell, 0, sizeof(cell));
      for (i = 0; i < sizeof(cell) && rd < slen; i++) {
        cell[i] = source[rd++];
        if (cell[i] >= ' ')
          cell[i] -= ' ';
      }
      target[wr] = (cell[0] & 0x3f) << 2;
      target[wr++] |= (cell[1] & 0x30) >> 4;
      target[wr] = (cell[1] & 0x0f) << 4;
      target[wr++] |= (cell[2] & 0x3c) >> 2;
      target[wr] = (cell[2] & 0x03) << 6;
      target[wr++] |= cell[3] & 0x3f;
      block += 3;
    }
    while (rd < slen && source[rd] > ' ')
      rd++;
    while (rd < slen && source[rd] != 0 && source[rd] <= ' ')
      rd++;
  }
  return (wr);
}
```