user: 请从给定的汇编指令推导出C源代码:

```asm
<_pscien>:
  endbr64
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x10,%rsp
  mov    %rdi,%r12
  mov    %esi,%ebx
  mov    %edx,%ebp
  mov    %fs:0x28,%rax
  mov    %rax,0x8(%rsp)
  xor    %eax,%eax
  mov    %rsp,%rdx
  lea    0x4(%rsp),%rsi
  lea    0x1(%rbx),%edi
  push   0x38(%rsp)
  push   0x38(%rsp)
  call   <_ecvt@plt>
  add    $0x10,%rsp
  cmpl   $0x0,(%rsp)
  je     L72
  lea    0x1(%r12),%rdx
  movb   $0x2d,(%r12)
L83:
  lea    0x1(%rax),%rcx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  test   %ebx,%ebx
  jle    L80
  lea    0x2(%rdx),%rdi
  movb   $0x2e,0x1(%rdx)
  jle    L67
  lea    0x3(%rdx),%rax
  lea    -0x1(%rbx),%r9d
  lea    0x4(%rdx,%r9,1),%rsi
  mov    $0x30,%r8d
  jmp    L104
L72:
  test   $0x2,%bpl
  je     L31
  lea    0x1(%r12),%rdx
  movb   $0x2b,(%r12)
  jmp    L83
L31:
  mov    %r12,%rdx
  test   $0x4,%bpl
  je     L83
  lea    0x1(%r12),%rdx
  movb   $0x20,(%r12)
  jmp    L83
L80:
  test   $0x8,%bpl
  jne    L95
  lea    0x1(%rdx),%rdi
  jmp    L67
L197:
  mov    %r8d,%edx
L196:
  mov    %dl,-0x1(%rax)
  add    $0x1,%rax
  cmp    %rsi,%rax
  je     L41
L104:
  movzbl (%rcx),%edx
  test   %dl,%dl
  je     L197
  add    $0x1,%rcx
  jmp    L196
L41:
  lea    0x1(%rdi,%r9,1),%rdi
L67:
  movb   $0x65,(%rdi)
  fldz
  fldt   0x30(%rsp)
  fucomip %st(1),%st
  fstp   %st(0)
  jp     L85
  jne    L85
L169:
  mov    0x4(%rsp),%edx
  test   %edx,%edx
  js     L50
  lea    0x2(%rdi),%rax
  movb   $0x2b,0x1(%rdi)
L153:
  mov    0x4(%rsp),%ecx
  cmp    $0x63,%ecx
  jle    L156
  movslq %ecx,%rdx
  imul   $0x51eb851f,%rdx,%rdx
  sar    $0x25,%rdx
  mov    %ecx,%esi
  sar    $0x1f,%esi
  sub    %esi,%edx
  lea    0x30(%rdx),%esi
  mov    %sil,(%rax)
  imul   $0x64,%edx,%edx
  sub    %edx,%ecx
  mov    %ecx,0x4(%rsp)
  lea    0x1(%rax),%rax
L156:
  mov    0x4(%rsp),%ecx
  movslq %ecx,%rdx
  imul   $0x66666667,%rdx,%rdx
  sar    $0x22,%rdx
  mov    %ecx,%esi
  sar    $0x1f,%esi
  sub    %esi,%edx
  lea    0x30(%rdx),%esi
  mov    %sil,(%rax)
  lea    (%rdx,%rdx,4),%edx
  add    %edx,%edx
  sub    %edx,%ecx
  add    $0x30,%ecx
  mov    %cl,0x1(%rax)
  add    $0x2,%rax
  mov    0x8(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L35
  add    $0x10,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  ret
L85:
  subl   $0x1,0x4(%rsp)
  jmp    L169
L50:
  lea    0x2(%rdi),%rax
  movb   $0x2d,0x1(%rdi)
  neg    %edx
  mov    %edx,0x4(%rsp)
  jmp    L153
L95:
  lea    0x2(%rdx),%rdi
  movb   $0x2e,0x1(%rdx)
  jmp    L67
L35:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
char *_pscien(long double r, register char *s, int n, int flags) {
  int sign, dp;
  register char *s1;
  s1 = _ecvt(r, n + 1, &dp, &sign);
  if (sign)
    *s++ = '-';
  else if (flags & 0x0002)
    *s++ = '+';
  else if (flags & 0x0004)
    *s++ = ' ';
  *s++ = *s1++;
  if ((n > 0) || (flags & 0x0008))
    *s++ = '.';
  while (--n >= 0)
    if (*s1)
      *s++ = *s1++;
    else
      *s++ = '0';
  *s++ = 'e';
  if (r != 0)
    --dp;
  if (dp < 0) {
    *s++ = '-';
    dp = -dp;
  } else {
    *s++ = '+';
  }
  if (dp >= 100) {
    *s++ = '0' + (dp / 100);
    dp %= 100;
  }
  *s++ = '0' + (dp / 10);
  *s++ = '0' + (dp % 10);
  return s;
}
```