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

```asm
<transpose>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  xor    %r13d,%r13d
  push   %r12
  movslq %esi,%r12
  push   %rbp
  movslq %ecx,%rbp
  push   %rbx
  sub    $0x68,%rsp
  mov    %rdi,0x38(%rsp)
  mov    %rdx,0x40(%rsp)
  mov    %r8d,0x4c(%rsp)
  mov    %fs:0x28,%rax
  mov    %rax,0x58(%rsp)
  xor    %eax,%eax
  lea    0x50(%rsp),%rax
  mov    %rax,0x8(%rsp)
  lea    0x58(%rsp),%rax
  mov    %rax,0x18(%rsp)
  lea    0x54(%rsp),%rax
  mov    %rax,0x10(%rsp)
  lea    0x5c(%rsp),%rax
  mov    %rax,0x20(%rsp)
  nopw   0x0(%rax,%rax,1)
L1:
  mov    0x38(%rsp),%rax
  mov    (%rax,%r13,8),%r14
  mov    0x40(%rsp),%rax
  mov    %r14,%rdi
  add    %r12,%r14
  mov    (%rax,%r13,8),%rbx
  call   <_mm_loadl_epi64@plt>
  mov    %r14,%rdi
  add    %r12,%r14
  mov    %eax,%r15d
  call   <_mm_loadl_epi64@plt>
  mov    %r15d,%edi
  mov    %eax,%esi
  call   <_mm_unpacklo_epi8@plt>
  mov    %r14,%rdi
  add    %r12,%r14
  mov    %eax,%r15d
  call   <_mm_loadl_epi64@plt>
  mov    %r14,%rdi
  add    %r12,%r14
  mov    %eax,0x28(%rsp)
  call   <_mm_loadl_epi64@plt>
  mov    0x28(%rsp),%edi
  mov    %eax,%esi
  call   <_mm_unpacklo_epi8@plt>
  mov    %r14,%rdi
  mov    %eax,0x34(%rsp)
  call   <_mm_loadl_epi64@plt>
  lea    (%r14,%r12,1),%rdx
  mov    %rdx,%rdi
  mov    %rdx,0x28(%rsp)
  mov    %eax,0x30(%rsp)
  call   <_mm_loadl_epi64@plt>
  mov    0x30(%rsp),%edi
  mov    %eax,%esi
  call   <_mm_unpacklo_epi8@plt>
  mov    0x28(%rsp),%rdx
  mov    %eax,%r14d
  add    %r12,%rdx
  mov    %rdx,%rdi
  mov    %rdx,0x28(%rsp)
  call   <_mm_loadl_epi64@plt>
  mov    0x28(%rsp),%rdx
  mov    %eax,0x50(%rsp)
  lea    (%rdx,%r12,1),%rdi
  call   <_mm_loadl_epi64@plt>
  mov    0x50(%rsp),%edi
  mov    %eax,%esi
  mov    %eax,0x54(%rsp)
  call   <_mm_unpacklo_epi8@plt>
  mov    0x34(%rsp),%r10d
  mov    %r15d,%edi
  mov    %eax,0x30(%rsp)
  mov    %r10d,%esi
  mov    %r10d,0x48(%rsp)
  call   <_mm_unpacklo_epi16@plt>
  mov    0x30(%rsp),%r8d
  mov    %r14d,%edi
  mov    %eax,0x28(%rsp)
  mov    %r8d,%esi
  mov    %r8d,0x34(%rsp)
  call   <_mm_unpacklo_epi16@plt>
  mov    0x28(%rsp),%edi
  mov    %eax,%esi
  mov    %eax,0x30(%rsp)
  call   <_mm_unpacklo_epi32@plt>
  mov    0x8(%rsp),%rsi
  mov    %rbx,%rdi
  mov    $0x8,%edx
  add    %rbp,%rbx
  mov    %eax,0x50(%rsp)
  call   <memcpy@plt>
  mov    0x18(%rsp),%rsi
  mov    $0x8,%edx
  mov    %rbx,%rdi
  add    %rbp,%rbx
  call   <memcpy@plt>
  mov    0x30(%rsp),%esi
  mov    0x28(%rsp),%edi
  call   <_mm_unpackhi_epi32@plt>
  mov    0x10(%rsp),%rsi
  mov    %rbx,%rdi
  mov    $0x8,%edx
  add    %rbp,%rbx
  mov    %eax,0x54(%rsp)
  call   <memcpy@plt>
  mov    0x20(%rsp),%rsi
  mov    $0x8,%edx
  mov    %rbx,%rdi
  add    %rbp,%rbx
  call   <memcpy@plt>
  mov    0x48(%rsp),%esi
  mov    %r15d,%edi
  call   <_mm_unpackhi_epi16@plt>
  mov    0x34(%rsp),%esi
  mov    %r14d,%edi
  mov    %eax,%r15d
  call   <_mm_unpackhi_epi16@plt>
  mov    %r15d,%edi
  mov    %eax,%esi
  mov    %eax,%r14d
  call   <_mm_unpacklo_epi32@plt>
  mov    0x8(%rsp),%rsi
  mov    %rbx,%rdi
  mov    $0x8,%edx
  mov    %eax,0x50(%rsp)
  call   <memcpy@plt>
  mov    0x18(%rsp),%rsi
  add    %rbp,%rbx
  add    $0x1,%r13
  mov    $0x8,%edx
  mov    %rbx,%rdi
  add    %rbp,%rbx
  call   <memcpy@plt>
  mov    %r14d,%esi
  mov    %r15d,%edi
  call   <_mm_unpackhi_epi32@plt>
  mov    0x10(%rsp),%rsi
  mov    $0x8,%edx
  mov    %rbx,%rdi
  mov    %eax,0x54(%rsp)
  call   <memcpy@plt>
  mov    0x20(%rsp),%rsi
  lea    (%rbx,%rbp,1),%rdi
  mov    $0x8,%edx
  call   <memcpy@plt>
  cmp    %r13d,0x4c(%rsp)
  jg     L1
  mov    0x58(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L8
  add    $0x68,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L8:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void transpose(unsigned char *src[], int in_p, unsigned char *dst[], int out_p, int num_8x8_to_transpose) {
  int idx8x8 = 0;
  __m128i x0, x1, x2, x3, x4, x5, x6, x7;
  do {
    unsigned char *in = src[idx8x8];
    unsigned char *out = dst[idx8x8];
    x0 = _mm_loadl_epi64((__m128i *)(in + 0 * in_p));
    x1 = _mm_loadl_epi64((__m128i *)(in + 1 * in_p));
    x0 = _mm_unpacklo_epi8(x0, x1);
    x2 = _mm_loadl_epi64((__m128i *)(in + 2 * in_p));
    x3 = _mm_loadl_epi64((__m128i *)(in + 3 * in_p));
    x1 = _mm_unpacklo_epi8(x2, x3);
    x4 = _mm_loadl_epi64((__m128i *)(in + 4 * in_p));
    x5 = _mm_loadl_epi64((__m128i *)(in + 5 * in_p));
    x2 = _mm_unpacklo_epi8(x4, x5);
    x6 = _mm_loadl_epi64((__m128i *)(in + 6 * in_p));
    x7 = _mm_loadl_epi64((__m128i *)(in + 7 * in_p));
    x3 = _mm_unpacklo_epi8(x6, x7);
    x4 = _mm_unpacklo_epi16(x0, x1);
    x5 = _mm_unpacklo_epi16(x2, x3);
    x6 = _mm_unpacklo_epi32(x4, x5);
    memcpy((out + 0 * out_p), (const char *)&(x6), 8);
    memcpy((out + 1 * out_p), (const char *)&(x6) + 8, 8);
    x7 = _mm_unpackhi_epi32(x4, x5);
    memcpy((out + 2 * out_p), (const char *)&(x7), 8);
    memcpy((out + 3 * out_p), (const char *)&(x7) + 8, 8);
    x4 = _mm_unpackhi_epi16(x0, x1);
    x5 = _mm_unpackhi_epi16(x2, x3);
    x6 = _mm_unpacklo_epi32(x4, x5);
    memcpy((out + 4 * out_p), (const char *)&(x6), 8);
    memcpy((out + 5 * out_p), (const char *)&(x6) + 8, 8);
    x7 = _mm_unpackhi_epi32(x4, x5);
    memcpy((out + 6 * out_p), (const char *)&(x7), 8);
    memcpy((out + 7 * out_p), (const char *)&(x7) + 8, 8);
  } while (++idx8x8 < num_8x8_to_transpose);
}
```