user: What is the c source code of the assembly code below:

```asm
<_pscien>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r12
  push   %rbx
  sub    $0x20,%rsp
  movsd  %xmm0,-0x28(%rbp)
  mov    %rdi,%rbx
  mov    %esi,-0x2c(%rbp)
  mov    %edx,-0x30(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x18(%rbp)
  xor    %eax,%eax
  mov    -0x2c(%rbp),%eax
  lea    0x1(%rax),%edi
  lea    -0x20(%rbp),%rdx
  lea    -0x1c(%rbp),%rcx
  mov    -0x28(%rbp),%rax
  mov    %rcx,%rsi
  movq   %rax,%xmm0
  call   <_ecvt@plt>
  mov    %rax,%r12
  mov    -0x20(%rbp),%eax
  test   %eax,%eax
  je     L23
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x2d,(%rax)
  jmp    L36
L23:
  mov    -0x30(%rbp),%eax
  and    $0x2,%eax
  test   %eax,%eax
  je     L63
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x2b,(%rax)
  jmp    L36
L63:
  mov    -0x30(%rbp),%eax
  and    $0x4,%eax
  test   %eax,%eax
  je     L36
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x20,(%rax)
L36:
  mov    %r12,%rdx
  lea    0x1(%rdx),%r12
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movzbl (%rdx),%edx
  mov    %dl,(%rax)
  cmpl   $0x0,-0x2c(%rbp)
  jg     L20
  mov    -0x30(%rbp),%eax
  and    $0x8,%eax
  test   %eax,%eax
  je     L99
L20:
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x2e,(%rax)
  jmp    L99
L61:
  movzbl (%r12),%eax
  test   %al,%al
  je     L83
  mov    %r12,%rdx
  lea    0x1(%rdx),%r12
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movzbl (%rdx),%edx
  mov    %dl,(%rax)
  jmp    L99
L83:
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x30,(%rax)
L99:
  subl   $0x1,-0x2c(%rbp)
  cmpl   $0x0,-0x2c(%rbp)
  jns    L61
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x65,(%rax)
  pxor   %xmm0,%xmm0
  ucomisd -0x28(%rbp),%xmm0
  jp     L71
  pxor   %xmm0,%xmm0
  ucomisd -0x28(%rbp),%xmm0
  je     L15
L71:
  mov    -0x1c(%rbp),%eax
  sub    $0x1,%eax
  mov    %eax,-0x1c(%rbp)
L15:
  mov    -0x1c(%rbp),%eax
  test   %eax,%eax
  jns    L72
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x2d,(%rax)
  mov    -0x1c(%rbp),%eax
  neg    %eax
  mov    %eax,-0x1c(%rbp)
  jmp    L126
L72:
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  movb   $0x2b,(%rax)
L126:
  mov    -0x1c(%rbp),%eax
  cmp    $0x63,%eax
  jle    L46
  mov    -0x1c(%rbp),%eax
  movslq %eax,%rdx
  imul   $0x51eb851f,%rdx,%rdx
  shr    $0x20,%rdx
  sar    $0x5,%edx
  sar    $0x1f,%eax
  mov    %eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  lea    0x30(%rax),%edx
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  mov    %dl,(%rax)
  mov    -0x1c(%rbp),%edx
  movslq %edx,%rax
  imul   $0x51eb851f,%rax,%rax
  shr    $0x20,%rax
  sar    $0x5,%eax
  mov    %edx,%ecx
  sar    $0x1f,%ecx
  sub    %ecx,%eax
  imul   $0x64,%eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  mov    %eax,-0x1c(%rbp)
L46:
  mov    -0x1c(%rbp),%eax
  movslq %eax,%rdx
  imul   $0x66666667,%rdx,%rdx
  shr    $0x20,%rdx
  sar    $0x2,%edx
  sar    $0x1f,%eax
  mov    %eax,%ecx
  mov    %edx,%eax
  sub    %ecx,%eax
  lea    0x30(%rax),%edx
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  mov    %dl,(%rax)
  mov    -0x1c(%rbp),%edx
  movslq %edx,%rax
  imul   $0x66666667,%rax,%rax
  shr    $0x20,%rax
  sar    $0x2,%eax
  mov    %edx,%esi
  sar    $0x1f,%esi
  sub    %esi,%eax
  mov    %eax,%ecx
  mov    %ecx,%eax
  shl    $0x2,%eax
  add    %ecx,%eax
  add    %eax,%eax
  mov    %edx,%ecx
  sub    %eax,%ecx
  mov    %ecx,%eax
  lea    0x30(%rax),%edx
  mov    %rbx,%rax
  lea    0x1(%rax),%rbx
  mov    %dl,(%rax)
  mov    %rbx,%rax
  mov    -0x18(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L6
  call   <__stack_chk_fail@plt>
L6:
  add    $0x20,%rsp
  pop    %rbx
  pop    %r12
  pop    %rbp
  ret
```

assistant: ```c
char *_pscien(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;
}
```