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

```asm
<buf2xys>:
  endbr64
  push   %r15
  mov    %rdi,%r10
  mov    %esi,%edi
  push   %r14
  mov    $0x1f,%r14d
  push   %r13
  sub    %ecx,%r14d
  mov    %r9,%r13
  push   %r12
  push   %rbp
  push   %rbx
  mov    %edx,-0x4(%rsp)
  cmp    $0x1e,%r14d
  jg     L85
  mov    %ecx,%r12d
  xor    %ebp,%ebp
  xor    %r11d,%r11d
  xor    %r9d,%r9d
  mov    $0x1f,%esi
  mov    $0xfffffffe,%ebx
  nopw   0x0(%rax,%rax,1)
L18:
  mov    %r9d,%eax
  mov    %r9d,%r15d
  mov    %r9d,%ecx
  add    $0x2,%r9d
  sar    $0x3,%eax
  not    %ecx
  lea    0x1(%r15),%edx
  cltq
  and    $0x7,%ecx
  sar    $0x3,%edx
  movzbl (%r10,%rax,1),%eax
  movslq %edx,%rdx
  movzbl (%r10,%rdx,1),%edx
  sar    %cl,%eax
  mov    %ebx,%ecx
  sub    %r15d,%ecx
  and    $0x1,%eax
  and    $0x7,%ecx
  sar    %cl,%edx
  mov    %esi,%ecx
  sub    $0x1,%esi
  and    $0x1,%edx
  shl    %cl,%eax
  shl    %cl,%edx
  or     %eax,%ebp
  or     %edx,%r11d
  cmp    %r14d,%esi
  jne    L18
  mov    %r11d,-0x18(%rsp)
  add    %r12d,%r12d
  mov    %ebp,-0x14(%rsp)
L40:
  test   %r8d,%r8d
  jle    L58
  mov    %edi,%eax
  lea    -0x1(%r8),%edx
  mov    0x38(%rsp),%r15
  mov    $0xfffffffe,%ebp
  shr    $0x1f,%eax
  add    %edi,%eax
  lea    0x4(%r13,%rdx,4),%rdi
  mov    %r14d,%edx
  sar    %eax
  mov    %rdi,-0x10(%rsp)
  neg    %eax
  sub    %eax,%edx
  lea    0x1f(%rax),%ebx
  lea    -0x40(%rdx,%rdx,1),%eax
  mov    %eax,-0x8(%rsp)
L26:
  mov    -0x14(%rsp),%r11d
  mov    -0x18(%rsp),%r9d
  mov    %r12d,%edi
  mov    %r14d,%esi
  cmp    %r14d,%ebx
  jge    L60
  nopl   (%rax)
L81:
  mov    %edi,%eax
  mov    %edi,%r8d
  mov    %edi,%ecx
  add    $0x2,%edi
  sar    $0x3,%eax
  not    %ecx
  lea    0x1(%r8),%edx
  cltq
  and    $0x7,%ecx
  sar    $0x3,%edx
  movzbl (%r10,%rax,1),%eax
  movslq %edx,%rdx
  movzbl (%r10,%rdx,1),%edx
  sar    %cl,%eax
  mov    %ebp,%ecx
  sub    %r8d,%ecx
  and    $0x1,%eax
  and    $0x7,%ecx
  sar    %cl,%edx
  mov    %esi,%ecx
  sub    $0x1,%esi
  and    $0x1,%edx
  shl    %cl,%eax
  shl    %cl,%edx
  or     %eax,%r11d
  or     %edx,%r9d
  cmp    %esi,%ebx
  jne    L81
  mov    -0x8(%rsp),%eax
  lea    0x2(%r12,%rax,1),%r12d
L60:
  mov    %r9d,0x0(%r13)
  add    $0x4,%r15
  add    $0x4,%r13
  mov    %r11d,-0x4(%r15)
  cmp    %r13,-0x10(%rsp)
  jne    L26
L58:
  mov    -0x4(%rsp),%eax
  mov    %eax,%edx
  sub    $0x1,%edx
  js     L67
  mov    0x40(%rsp),%rbx
  lea    (%r12,%rax,1),%edi
  add    %edx,%r12d
  mov    (%rbx),%rsi
  mov    %rbx,%r8
  cs nopw 0x0(%rax,%rax,1)
L30:
  mov    %r12d,%eax
  mov    %edx,%ecx
  sub    %edx,%eax
  sub    %edi,%ecx
  sar    $0x3,%eax
  and    $0x7,%ecx
  cltq
  movzbl (%r10,%rax,1),%eax
  sar    %cl,%eax
  mov    %edx,%ecx
  and    $0x1,%eax
  shl    %cl,%rax
  or     %rax,%rsi
  mov    %rsi,(%r8)
  sub    $0x1,%edx
  jae    L30
L67:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L85:
  movl   $0x0,-0x14(%rsp)
  xor    %r12d,%r12d
  movl   $0x0,-0x18(%rsp)
  jmp    L40
```

assistant: ```c
void buf2xys(const unsigned char *const buf, const int mapbits, const int metabits, const int skip, const int n, unsigned int *x, unsigned int *y, unsigned long long *meta) {
  int i, j;
  int offbits = 0;
  unsigned int xx = 0, yy = 0;
  for (i = 31; i > 31 - skip; i--) {
    int y0 = (buf[offbits / 8] >> (7 - offbits % 8)) & 1;
    offbits++;
    int x0 = (buf[offbits / 8] >> (7 - offbits % 8)) & 1;
    offbits++;
    xx |= x0 << i;
    yy |= y0 << i;
  }
  for (j = 0; j < n; j++) {
    unsigned int xj = xx;
    unsigned int yj = yy;
    for (i = 31 - skip; i > 31 - mapbits / 2; i--) {
      int y0 = (buf[offbits / 8] >> (7 - offbits % 8)) & 1;
      offbits++;
      int x0 = (buf[offbits / 8] >> (7 - offbits % 8)) & 1;
      offbits++;
      xj |= x0 << i;
      yj |= y0 << i;
    }
    x[j] = xj;
    y[j] = yj;
  }
  for (i = metabits - 1; i >= 0; i--) {
    unsigned long long m = (buf[offbits / 8] >> (7 - offbits % 8)) & 1;
    offbits++;
    *meta |= m << i;
  }
}
```