user: What would the C source look like for the assembly code provided here?

```asm
<utf8char>:
  endbr64
  mov    %rsi,%rax
  lea    -0xfffe(%rsi),%rdx
  cmp    $0x1,%rdx
  jbe    L25
  cmp    $0xd,%rsi
  jne    L80
L25:
  mov    %rdi,%rax
  ret
L80:
  cmp    $0x7f,%rsi
  ja     L69
  mov    %sil,(%rdi)
  lea    0x1(%rdi),%rdi
  jmp    L25
L69:
  cmp    $0x7ff,%rsi
  ja     L13
  mov    %rsi,%rdx
  shr    $0x6,%rdx
  sub    $0x40,%edx
  mov    %dl,(%rdi)
  and    $0x3f,%eax
  add    $0xffffff80,%eax
  mov    %al,0x1(%rdi)
  lea    0x2(%rdi),%rdi
  jmp    L25
L13:
  cmp    $0xffff,%rsi
  ja     L72
  mov    %rsi,%rdx
  shr    $0xc,%rdx
  sub    $0x20,%edx
  mov    %dl,(%rdi)
  mov    %rsi,%rdx
  shr    $0x6,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x1(%rdi)
  and    $0x3f,%eax
  add    $0xffffff80,%eax
  mov    %al,0x2(%rdi)
  lea    0x3(%rdi),%rdi
  jmp    L25
L72:
  cmp    $0x1fffff,%rsi
  ja     L45
  mov    %rsi,%rdx
  shr    $0x12,%rdx
  sub    $0x10,%edx
  mov    %dl,(%rdi)
  mov    %rsi,%rdx
  shr    $0xc,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x1(%rdi)
  mov    %rsi,%rdx
  shr    $0x6,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x2(%rdi)
  and    $0x3f,%eax
  add    $0xffffff80,%eax
  mov    %al,0x3(%rdi)
  lea    0x4(%rdi),%rdi
  jmp    L25
L45:
  cmp    $0x3ffffff,%rsi
  ja     L64
  mov    %rsi,%rdx
  shr    $0x18,%rdx
  sub    $0x8,%edx
  mov    %dl,(%rdi)
  mov    %rsi,%rdx
  shr    $0x12,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x1(%rdi)
  mov    %rsi,%rdx
  shr    $0xc,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x2(%rdi)
  mov    %rsi,%rdx
  shr    $0x6,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x3(%rdi)
  and    $0x3f,%eax
  add    $0xffffff80,%eax
  mov    %al,0x4(%rdi)
  lea    0x5(%rdi),%rdi
  jmp    L25
L64:
  cmp    $0x7fffffff,%rsi
  ja     L25
  mov    %rsi,%rdx
  shr    $0x1e,%rdx
  sub    $0x4,%edx
  mov    %dl,(%rdi)
  mov    %rsi,%rdx
  shr    $0x18,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x1(%rdi)
  mov    %rsi,%rdx
  shr    $0x12,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x2(%rdi)
  mov    %rsi,%rdx
  shr    $0xc,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x3(%rdi)
  mov    %rsi,%rdx
  shr    $0x6,%rdx
  and    $0x3f,%edx
  add    $0xffffff80,%edx
  mov    %dl,0x4(%rdi)
  and    $0x3f,%eax
  add    $0xffffff80,%eax
  mov    %al,0x5(%rdi)
  lea    0x6(%rdi),%rdi
  jmp    L25
```

assistant: ```c
unsigned char *utf8char(unsigned char *dst, unsigned long value) {
  if (value == '\r' || value == 0xFFFE || value == 0xFFFF) {
    ;
  } else if (value < 0x80) {
    *dst++ = value;
  } else if (value < 0x800) {
    *dst++ = 0xC0 + ((value >> 6) & 0x1F);
    *dst++ = 0x80 + ((value >> 0) & 0x3F);
  } else if (value < 0x10000) {
    *dst++ = 0xE0 + ((value >> 12) & 0x0F);
    *dst++ = 0x80 + ((value >> 6) & 0x3F);
    *dst++ = 0x80 + ((value >> 0) & 0x3F);
  } else if (value < 0x200000) {
    *dst++ = 0xF0 + ((value >> 18) & 0x07);
    *dst++ = 0x80 + ((value >> 12) & 0x3F);
    *dst++ = 0x80 + ((value >> 6) & 0x3F);
    *dst++ = 0x80 + ((value >> 0) & 0x3F);
  } else if (value < 0x4000000) {
    *dst++ = 0xF8 + ((value >> 24) & 0x03);
    *dst++ = 0x80 + ((value >> 18) & 0x3F);
    *dst++ = 0x80 + ((value >> 12) & 0x3F);
    *dst++ = 0x80 + ((value >> 6) & 0x3F);
    *dst++ = 0x80 + ((value >> 0) & 0x3F);
  } else if (value < 0x80000000) {
    *dst++ = 0xFC + ((value >> 30) & 0x01);
    *dst++ = 0x80 + ((value >> 24) & 0x3F);
    *dst++ = 0x80 + ((value >> 18) & 0x3F);
    *dst++ = 0x80 + ((value >> 12) & 0x3F);
    *dst++ = 0x80 + ((value >> 6) & 0x3F);
    *dst++ = 0x80 + ((value >> 0) & 0x3F);
  }
  return dst;
}
```