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

```asm
<get_double_excitation>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x28,%rsp
  mov    %rdi,%r13
  mov    %rsi,%r12
  mov    %edx,%ebx
  mov    $0x10,%edi
  call   <malloc@plt>
  mov    %rax,0x8(%rsp)
  movslq %ebx,%rax
  mov    %rax,0x10(%rsp)
  test   %rax,%rax
  je     L35
  lea    -0x8(,%rax,8),%rax
  add    %rax,%r13
  add    %rax,%r12
  mov    $0x0,%r14d
  movl   $0x0,0x1c(%rsp)
  movl   $0x2,0x18(%rsp)
  mov    $0x0,%r15d
  jmp    L93
L32:
  mov    %rbp,%rdi
  call   <trailz@plt>
  mov    0x18(%rsp),%esi
  movslq %esi,%rdx
  add    %r14d,%eax
  mov    0x8(%rsp),%rcx
  mov    %eax,(%rcx,%rdx,4)
  add    $0x1,%esi
  mov    %esi,0x18(%rsp)
L47:
  cmpl   $0x1,0x4(%rsp)
  je     L38
  cmpl   $0x2,0x4(%rsp)
  je     L57
L10:
  add    $0x1,%r15
  sub    $0x8,%r13
  sub    $0x8,%r12
  add    $0x40,%r14d
  cmp    0x10(%rsp),%r15
  je     L35
L93:
  mov    0x0(%r13),%rax
  xor    (%r12),%rax
  mov    %rax,%rbp
  and    (%r12),%rbp
  and    0x0(%r13),%rax
  mov    %rax,%rbx
  mov    %rbp,%rdi
  call   <popcount@plt>
  mov    %eax,(%rsp)
  mov    %rbx,%rdi
  call   <popcount@plt>
  mov    %eax,0x4(%rsp)
  cmpl   $0x1,(%rsp)
  je     L32
  cmpl   $0x2,(%rsp)
  jne    L47
  mov    %rbp,%rdi
  call   <trailz@plt>
  mov    %eax,%ecx
  lea    (%rax,%r14,1),%eax
  mov    0x8(%rsp),%rdx
  mov    %eax,0x8(%rdx)
  mov    $0x1,%edi
  shl    %cl,%rdi
  not    %rdi
  and    %rbp,%rdi
  call   <trailz@plt>
  add    %r14d,%eax
  mov    0x8(%rsp),%rdx
  mov    %eax,0xc(%rdx)
  jmp    L47
L38:
  mov    %rbx,%rdi
  call   <trailz@plt>
  mov    0x1c(%rsp),%ecx
  movslq %ecx,%rdx
  add    %r14d,%eax
  mov    0x8(%rsp),%rsi
  mov    %eax,(%rsi,%rdx,4)
  add    $0x1,%ecx
  mov    %ecx,0x1c(%rsp)
  jmp    L10
L57:
  mov    %rbx,%rdi
  call   <trailz@plt>
  mov    %eax,%ecx
  lea    (%rax,%r14,1),%eax
  mov    0x8(%rsp),%rbp
  mov    %eax,0x0(%rbp)
  mov    $0x1,%edi
  shl    %cl,%rdi
  not    %rdi
  and    %rbx,%rdi
  call   <trailz@plt>
  add    %r14d,%eax
  mov    %eax,0x4(%rbp)
  jmp    L10
L35:
  mov    0x8(%rsp),%rax
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
int *get_double_excitation(uint64_t *str1, uint64_t *str2, int nset) {
  size_t p;
  int *ijab = malloc(sizeof(int) * 4);
  int particle_ind = 2;
  int hole_ind = 0;
  for (p = 0; p < nset; ++p) {
    size_t pp = nset - p - 1;
    uint64_t str_tmp = str1[pp] ^ str2[pp];
    uint64_t str_particle = str_tmp & str2[pp];
    uint64_t str_hole = str_tmp & str1[pp];
    int n_particle = popcount(str_particle);
    int n_hole = popcount(str_hole);
    if (n_particle == 1) {
      ijab[particle_ind] = trailz(str_particle) + 64 * p;
      particle_ind++;
    } else if (n_particle == 2) {
      int a = trailz(str_particle);
      ijab[2] = a + 64 * p;
      str_particle &= ~(1ULL << a);
      int b = trailz(str_particle);
      ijab[3] = b + 64 * p;
    }
    if (n_hole == 1) {
      ijab[hole_ind] = trailz(str_hole) + 64 * p;
      hole_ind++;
    } else if (n_hole == 2) {
      int i = trailz(str_hole);
      ijab[0] = i + 64 * p;
      str_hole &= ~(1ULL << i);
      int j = trailz(str_hole);
      ijab[1] = j + 64 * p;
    }
  }
  return ijab;
}
```