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

```asm
<draw_ellipse>:
  endbr64
  push   %r15
  mov    %ecx,%eax
  mov    %edx,%r15d
  push   %r14
  imul   %edx,%r15d
  mov    %edi,%r14d
  push   %r13
  imul   %ecx,%eax
  mov    %esi,%r13d
  push   %r12
  mov    %edx,%r12d
  mov    %r8d,%edx
  push   %rbp
  mov    %ecx,%ebp
  push   %rbx
  mov    %r8d,%ebx
  sub    $0x38,%rsp
  mov    %esi,0x8(%rsp)
  lea    (%rcx,%rsi,1),%esi
  mov    %r15d,0x1c(%rsp)
  mov    %eax,0x14(%rsp)
  call   <draw_pixel@plt>
  mov    %r13d,%esi
  mov    %r14d,%edi
  mov    %ebx,%edx
  sub    %ebp,%esi
  lea    0x1(%r14),%r13d
  call   <draw_pixel@plt>
  mov    %r15d,%eax
  mov    %r15d,%r8d
  lea    (%r15,%r15,1),%ecx
  imul   %ebp,%eax
  sar    $0x2,%r8d
  xor    %r15d,%r15d
  mov    %r14d,0x28(%rsp)
  mov    %r12d,0x2c(%rsp)
  mov    %r13d,%r12d
  mov    %r15d,%r13d
  mov    %ecx,0x24(%rsp)
  lea    (%rax,%rax,1),%r10d
  sub    %eax,%r8d
  mov    0x14(%rsp),%eax
  mov    %r8d,%r15d
  add    %eax,%eax
  mov    %eax,0x18(%rsp)
  lea    (%r14,%r14,1),%eax
  mov    %r10d,%r14d
  mov    %eax,0x20(%rsp)
  jmp    L38
L40:
  mov    0x8(%rsp),%esi
  mov    %r12d,%edi
  mov    %ebx,%edx
  sub    %ebp,%esi
  mov    %esi,0xc(%rsp)
  call   <draw_pixel@plt>
  mov    0x20(%rsp),%r11d
  mov    0xc(%rsp),%esi
  mov    %ebx,%edx
  sub    %r12d,%r11d
  mov    %r11d,%edi
  mov    %r11d,0x10(%rsp)
  call   <draw_pixel@plt>
  mov    0x8(%rsp),%esi
  mov    %r12d,%edi
  mov    %ebx,%edx
  add    $0x1,%r12d
  add    %ebp,%esi
  mov    %esi,0xc(%rsp)
  call   <draw_pixel@plt>
  mov    0xc(%rsp),%esi
  mov    0x10(%rsp),%edi
  mov    %ebx,%edx
  call   <draw_pixel@plt>
L38:
  mov    0x14(%rsp),%eax
  add    %r13d,%eax
  add    %eax,%r15d
  js     L58
  sub    0x24(%rsp),%r14d
  sub    $0x1,%ebp
  sub    %r14d,%r15d
L58:
  add    0x18(%rsp),%r13d
  cmp    %r13d,%r14d
  jg     L40
  mov    0x28(%rsp),%r14d
  mov    0x8(%rsp),%r15d
  mov    %ebx,%edx
  xor    %r13d,%r13d
  mov    0x2c(%rsp),%r12d
  mov    %r15d,%esi
  lea    (%r12,%r14,1),%edi
  call   <draw_pixel@plt>
  mov    %r14d,%edi
  mov    %r15d,%esi
  mov    %ebx,%edx
  sub    %r12d,%edi
  call   <draw_pixel@plt>
  mov    0x14(%rsp),%ecx
  mov    %r14d,0x8(%rsp)
  mov    %r13d,%r14d
  mov    %ecx,%eax
  sar    $0x2,%ecx
  imul   %r12d,%eax
  mov    %ecx,%ebp
  lea    (%rax,%rax,1),%r9d
  sub    %eax,%ebp
  mov    0x1c(%rsp),%eax
  mov    %r9d,%r13d
  add    %eax,%eax
  mov    %eax,0x20(%rsp)
  mov    %r15d,%eax
  lea    -0x1(%r15),%r15d
  add    %eax,%eax
  mov    %eax,0x24(%rsp)
  jmp    L22
L49:
  mov    0x8(%rsp),%eax
  mov    %r15d,%esi
  mov    %ebx,%edx
  lea    (%r12,%rax,1),%r11d
  mov    %r11d,%edi
  mov    %r11d,0x14(%rsp)
  call   <draw_pixel@plt>
  mov    0x8(%rsp),%r10d
  mov    %r15d,%esi
  mov    %ebx,%edx
  sub    %r12d,%r10d
  mov    %r10d,%edi
  mov    %r10d,0x10(%rsp)
  call   <draw_pixel@plt>
  mov    0x24(%rsp),%esi
  mov    0x14(%rsp),%edi
  mov    %ebx,%edx
  sub    %r15d,%esi
  sub    $0x1,%r15d
  mov    %esi,0xc(%rsp)
  call   <draw_pixel@plt>
  mov    0xc(%rsp),%esi
  mov    0x10(%rsp),%edi
  mov    %ebx,%edx
  call   <draw_pixel@plt>
L22:
  mov    0x1c(%rsp),%eax
  add    %r14d,%eax
  add    %eax,%ebp
  js     L56
  sub    0x18(%rsp),%r13d
  sub    $0x1,%r12d
  sub    %r13d,%ebp
L56:
  add    0x20(%rsp),%r14d
  cmp    %r14d,%r13d
  jge    L49
  add    $0x38,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
void draw_ellipse(int x, int y, int a, int b, int color) {
  int wx, wy;
  int thresh;
  int asq = a * a;
  int bsq = b * b;
  int xa, ya;
  draw_pixel(x, y + b, color);
  draw_pixel(x, y - b, color);
  wx = 0;
  wy = b;
  xa = 0;
  ya = asq * 2 * b;
  thresh = asq / 4 - asq * b;
  for (;;) {
    thresh += xa + bsq;
    if (thresh >= 0) {
      ya -= asq * 2;
      thresh -= ya;
      wy--;
    }
    xa += bsq * 2;
    wx++;
    if (xa >= ya)
      break;
    draw_pixel(x + wx, y - wy, color);
    draw_pixel(x - wx, y - wy, color);
    draw_pixel(x + wx, y + wy, color);
    draw_pixel(x - wx, y + wy, color);
  }
  draw_pixel(x + a, y, color);
  draw_pixel(x - a, y, color);
  wx = a;
  wy = 0;
  xa = bsq * 2 * a;
  ya = 0;
  thresh = bsq / 4 - bsq * a;
  for (;;) {
    thresh += ya + asq;
    if (thresh >= 0) {
      xa -= bsq * 2;
      thresh = thresh - xa;
      wx--;
    }
    ya += asq * 2;
    wy++;
    if (ya > xa)
      break;
    draw_pixel(x + wx, y - wy, color);
    draw_pixel(x - wx, y - wy, color);
    draw_pixel(x + wx, y + wy, color);
    draw_pixel(x - wx, y + wy, color);
  }
}
```