user: 请从给定的汇编指令推导出C源代码：

```asm
<_pscien>:
  endbr64
  push   %r12
  mov    %rdi,%r12
  push   %rbp
  mov    %edx,%ebp
  push   %rbx
  mov    %esi,%ebx
  lea    0x1(%rbx),%edi
  sub    $0x10,%rsp
  mov    %fs:0x28,%rax
  mov    %rax,0x8(%rsp)
  xor    %eax,%eax
  mov    %rsp,%rdx
  lea    0x4(%rsp),%rsi
  push   0x38(%rsp)
  push   0x38(%rsp)
  call   <_ecvt@plt>
  pop    %rcx
  pop    %rsi
  lea    0x1(%r12),%rdx
  mov    (%rsp),%edi
  test   %edi,%edi
  je     L118
  movb   $0x2d,(%r12)
L56:
  lea    0x1(%rax),%rcx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  test   %ebx,%ebx
  jle    L85
L37:
  lea    -0x1(%rbx),%eax
  lea    0x2(%rdx),%rdi
  movb   $0x2e,0x1(%rdx)
  lea    0x3(%rdx,%rax,1),%rsi
  mov    %rdi,%rax
  jmp    L70
  nopl   0x0(%rax,%rax,1)
L68:
  mov    %dl,-0x1(%rax)
  add    $0x1,%rcx
  cmp    %rax,%rsi
  je     L102
L70:
  movzbl (%rcx),%edx
  add    $0x1,%rax
  test   %dl,%dl
  jne    L68
  mov    $0x30,%edx
  mov    %dl,-0x1(%rax)
  cmp    %rax,%rsi
  jne    L70
L102:
  lea    (%rdi,%rbx,1),%rcx
L30:
  fldz
  movb   $0x65,(%rcx)
  mov    0x4(%rsp),%edx
  fldt   0x30(%rsp)
  fucomip %st(1),%st
  fstp   %st(0)
  jp     L106
  jne    L106
  lea    0x2(%rcx),%rax
  test   %edx,%edx
  js     L40
L111:
  movb   $0x2b,0x1(%rcx)
L54:
  cmp    $0x63,%edx
  jle    L206
  mov    %edx,%esi
  lea    0x3(%rcx),%rax
  imul   $0x51eb851f,%rsi,%rsi
  shr    $0x25,%rsi
  lea    0x30(%rsi),%edi
  imul   $0x64,%esi,%esi
  mov    %dil,0x2(%rcx)
  sub    %esi,%edx
L206:
  mov    %edx,%ecx
  mov    $0xcccccccd,%esi
  add    $0x2,%rax
  imul   %rsi,%rcx
  shr    $0x23,%rcx
  lea    0x30(%rcx),%esi
  lea    (%rcx,%rcx,4),%ecx
  add    %ecx,%ecx
  mov    %sil,-0x2(%rax)
  sub    %ecx,%edx
  add    $0x30,%edx
  mov    %dl,-0x1(%rax)
  mov    0x8(%rsp),%rdx
  sub    %fs:0x28,%rdx
  jne    L182
  add    $0x10,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  ret
  nop
L106:
  sub    $0x1,%edx
  lea    0x2(%rcx),%rax
  test   %edx,%edx
  jns    L111
L40:
  movb   $0x2d,0x1(%rcx)
  neg    %edx
  jmp    L54
  nopl   0x0(%rax,%rax,1)
L118:
  test   $0x2,%bpl
  je     L207
  movb   $0x2b,(%r12)
  lea    0x1(%rax),%rcx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  test   %ebx,%ebx
  jg     L37
L85:
  and    $0x8,%ebp
  je     L116
  movb   $0x2e,0x1(%rdx)
  lea    0x2(%rdx),%rcx
  jmp    L30
  cs nopw 0x0(%rax,%rax,1)
L207:
  test   $0x4,%bpl
  je     L52
  movb   $0x20,(%r12)
  jmp    L56
L116:
  lea    0x1(%rdx),%rcx
  jmp    L30
  nopl   0x0(%rax)
L52:
  mov    %r12,%rdx
  jmp    L56
L182:
  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;
}
```