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

```asm
<MessageExpansion256>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  mov    %rdi,%rbx
  sub    $0x68,%rsp
  mov    %rsi,0x18(%rsp)
  mov    %rdx,0x28(%rsp)
  mov    %fs:0x28,%rax
  mov    %rax,0x58(%rsp)
  xor    %eax,%eax
  lea    0xc0(%rdi),%rax
  movl   $0x20,0xc(%rsp)
  mov    %rax,0x10(%rsp)
  lea    0x10(%rsi),%rax
  mov    %rax,0x20(%rsp)
L48:
  mov    0xc(%rsp),%eax
  lea    -0x10(%rax),%r13d
  cmp    %r13d,%eax
  jle    L104
  mov    0x10(%rsp),%rax
  lea    0x40(%rsp),%r15
  lea    0x30(%rsp),%rbp
  lea    0x50(%rsp),%r12
  lea    -0x80(%rax),%r14
  nopl   (%rax)
L54:
  mov    -0x3c(%r14),%eax
  mov    0x18(%rsp),%rdx
  mov    %r15,%rsi
  mov    %rbp,%rdi
  mov    %eax,0x30(%rsp)
  mov    -0x38(%r14),%eax
  mov    %eax,0x34(%rsp)
  mov    -0x34(%r14),%eax
  mov    %eax,0x38(%rsp)
  mov    -0x40(%r14),%eax
  mov    %eax,0x3c(%rsp)
  call   <roundAESkeyfirst@plt>
  mov    %r15,%rcx
  mov    %r14,%rdx
  mov    %r15,%rax
L71:
  mov    (%rax),%edi
  add    $0x4,%rax
  xor    -0x10(%rdx),%edi
  add    $0x4,%rdx
  mov    %edi,-0x4(%rdx)
  cmp    %rax,%r12
  jne    L71
  cmp    $0x10,%r13d
  jne    L31
  mov    0x28(%rsp),%rsi
  mov    (%rsi),%eax
  xor    %eax,0x40(%rbx)
  mov    0x4(%rsi),%eax
  xor    %eax,0x44(%rbx)
L31:
  mov    -0x2c(%r14),%eax
  mov    0x20(%rsp),%rdx
  mov    %r15,%rsi
  mov    %rbp,%rdi
  mov    %rcx,(%rsp)
  mov    %eax,0x30(%rsp)
  mov    -0x28(%r14),%eax
  mov    %eax,0x34(%rsp)
  mov    -0x24(%r14),%eax
  mov    %eax,0x38(%rsp)
  mov    -0x30(%r14),%eax
  mov    %eax,0x3c(%rsp)
  call   <roundAESkeyfirst@plt>
  mov    (%rsp),%rcx
  lea    0x10(%r14),%rax
L77:
  mov    (%rcx),%edx
  add    $0x4,%rcx
  xor    -0x10(%rax),%edx
  add    $0x4,%rax
  mov    %edx,-0x4(%rax)
  cmp    %rcx,%r12
  jne    L77
  cmp    $0x78,%r13d
  je     L42
  add    $0x8,%r13d
  add    $0x20,%r14
  cmp    %r13d,0xc(%rsp)
  jg     L54
  jmp    L104
  nopl   0x0(%rax,%rax,1)
L42:
  mov    0x28(%rsp),%rsi
  mov    (%rsi),%eax
  xor    %eax,0x1f0(%rbx)
  mov    0x4(%rsi),%eax
  xor    %eax,0x1fc(%rbx)
L104:
  mov    0xc(%rsp),%esi
  mov    0x10(%rsp),%rax
  lea    0xf(%rsi),%edx
  sub    $0x40,%rax
  cmp    %edx,%esi
  jg     L49
  nopw   0x0(%rax,%rax,1)
L37:
  mov    -0x40(%rax),%edx
  xor    -0xc(%rax),%edx
  add    $0x4,%rax
  mov    %edx,-0x4(%rax)
  cmp    0x10(%rsp),%rax
  jne    L37
L49:
  addl   $0x20,0xc(%rsp)
  mov    0xc(%rsp),%eax
  subq   $0xffffffffffffff80,0x10(%rsp)
  cmp    $0xa0,%eax
  jne    L48
  mov    0x58(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L76
  add    $0x68,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L76:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void MessageExpansion256(uint32_t rk[(12 * 4 * (3))], uint32_t salt[8], uint32_t counter[2]) {
  int i, j, k;
  uint32_t input[4], output[4];
  for (k = 0; k < 4; k++) {
    for (i = 16 + 32 * k; i < 32 + 32 * k;) {
      input[0] = rk[i - 15];
      input[1] = rk[i - 14];
      input[2] = rk[i - 13];
      input[3] = rk[i - 16];
      roundAESkeyfirst(input, output, salt);
      for (j = 0; j < 4; j++)
        rk[i + j] = output[j] ^ rk[i + j - 4];
      if (i == 16) {
        rk[16] ^= counter[0];
        rk[17] ^= counter[1];
      }
      if (i == 84) {
        rk[86] ^= counter[1];
        rk[87] ^= counter[0];
      }
      i += 4;
      input[0] = rk[i - 15];
      input[1] = rk[i - 14];
      input[2] = rk[i - 13];
      input[3] = rk[i - 16];
      roundAESkeyfirst(input, output, salt + 4);
      for (j = 0; j < 4; j++)
        rk[i + j] = output[j] ^ rk[i + j - 4];
      if (i == 56) {
        rk[57] ^= counter[1];
        rk[58] ^= counter[0];
      }
      if (i == 124) {
        rk[124] ^= counter[0];
        rk[127] ^= counter[1];
      }
      i += 4;
    }
    for (i = 32 + 32 * k; i < 48 + 32 * k; i++)
      rk[i] = rk[i - 16] ^ rk[i - 3];
  }
  return;
}
```