user: Converte this assembly snippet into its equivalent C code:

```asm
<cov>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbx
  sub    $0x68,%rsp
  mov    %rdi,-0x68(%rbp)
  mov    %rsi,-0x70(%rbp)
  mov    %rdx,-0x78(%rbp)
  mov    %rcx,-0x80(%rbp)
  mov    %r8,-0x88(%rbp)
  mov    %r9,-0x90(%rbp)
  mov    -0x70(%rbp),%rax
  mov    %rax,%rdx
  sub    $0x1,%rdx
  mov    %rdx,-0x48(%rbp)
  mov    %rax,%r14
  mov    $0x0,%r15d
  mov    -0x80(%rbp),%rax
  mov    %rax,%rdx
  sub    $0x1,%rdx
  mov    %rdx,-0x40(%rbp)
  mov    %rax,%r12
  mov    $0x0,%r13d
  mov    -0x80(%rbp),%rbx
  mov    %rbx,%rax
  sub    $0x1,%rax
  mov    %rax,-0x38(%rbp)
  mov    %rbx,%r10
  mov    $0x0,%r11d
  mov    -0x68(%rbp),%rax
  cmp    -0x78(%rbp),%rax
  sete   %al
  movzbl %al,%eax
  mov    %eax,%edi
  call   <assert@plt>
  movq   $0x0,-0x58(%rbp)
  jmp    L30
L39:
  mov    -0x58(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x10(%rbp),%rax
  lea    (%rdx,%rax,1),%r12
  mov    -0x58(%rbp),%rcx
  mov    -0x88(%rbp),%rdx
  mov    -0x70(%rbp),%rsi
  mov    -0x68(%rbp),%rax
  mov    %rax,%rdi
  call   <mu@plt>
  movq   %xmm0,%rax
  mov    %rax,(%r12)
  addq   $0x1,-0x58(%rbp)
L30:
  mov    -0x58(%rbp),%rax
  cmp    -0x70(%rbp),%rax
  jb     L39
  movq   $0x0,-0x58(%rbp)
  jmp    L19
L56:
  mov    -0x58(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x18(%rbp),%rax
  lea    (%rdx,%rax,1),%r12
  mov    -0x58(%rbp),%rcx
  mov    -0x90(%rbp),%rdx
  mov    -0x80(%rbp),%rsi
  mov    -0x78(%rbp),%rax
  mov    %rax,%rdi
  call   <mu@plt>
  movq   %xmm0,%rax
  mov    %rax,(%r12)
  addq   $0x1,-0x58(%rbp)
L19:
  mov    -0x58(%rbp),%rax
  cmp    -0x80(%rbp),%rax
  jb     L56
  movq   $0x0,-0x58(%rbp)
  jmp    L43
L48:
  movq   $0x0,-0x50(%rbp)
  jmp    L12
L53:
  mov    -0x50(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x18(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x58(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x10(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%rdi
  mov    %rbx,%rax
  imul   -0x50(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x20(%rbp),%rax
  lea    (%rdx,%rax,1),%r12
  mov    -0x58(%rbp),%r9
  mov    -0x90(%rbp),%r8
  mov    -0x88(%rbp),%rcx
  mov    -0x80(%rbp),%rdx
  mov    -0x70(%rbp),%rsi
  mov    -0x68(%rbp),%rax
  sub    $0x8,%rsp
  push   -0x50(%rbp)
  movapd %xmm0,%xmm1
  movq   %rdi,%xmm0
  mov    %rax,%rdi
  call   <sigma@plt>
  add    $0x10,%rsp
  movq   %xmm0,%rax
  mov    -0x58(%rbp),%rdx
  mov    %rax,(%r12,%rdx,8)
  mov    %rbx,%rax
  imul   -0x58(%rbp),%rax
  lea    0x0(,%rax,8),%rdx
  mov    0x20(%rbp),%rax
  add    %rax,%rdx
  mov    -0x58(%rbp),%rax
  movsd  (%r12,%rax,8),%xmm0
  mov    -0x50(%rbp),%rax
  movsd  %xmm0,(%rdx,%rax,8)
  addq   $0x1,-0x50(%rbp)
L12:
  mov    -0x50(%rbp),%rax
  cmp    -0x58(%rbp),%rax
  jbe    L53
  addq   $0x1,-0x58(%rbp)
L43:
  mov    -0x58(%rbp),%rax
  cmp    -0x70(%rbp),%rax
  jb     L48
  nop
  nop
  lea    -0x28(%rbp),%rsp
  pop    %rbx
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  pop    %rbp
  ret
```

assistant: ```c
void cov(size_t xr, size_t xc, size_t yr, size_t yc, double X[xr][xc], double Y[yr][yc], double xm[xc], double ym[yc], double Z[xc][yc]) {
  size_t i, j;
  assert(xr == yr);
  for (i = 0; i < xc; i++)
    xm[i] = mu(xr, xc, X, i);
  for (i = 0; i < yc; i++)
    ym[i] = mu(yr, yc, Y, i);
  for (i = 0; i < xc; i++) {
    for (j = 0; j <= i; j++)
      Z[i][j] = Z[j][i] = sigma(xr, xc, yc, X, Y, xm[i], ym[j], i, j);
  }
}
```