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

```asm
<unpackforblock4_64>:
  endbr64
  mov    (%rsi),%r9
  mov    %edi,%eax
  mov    %rdx,%r8
  mov    (%rdx),%rdx
  mov    $0x20,%ecx
  mov    (%r9),%edi
  mov    0x4(%r9),%r10d
  add    $0x40,%r9
  mov    %r9,(%rsi)
  mov    %edi,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,(%rdx)
  mov    %edi,%esi
  sar    $0x4,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x4(%rdx)
  mov    %edi,%esi
  sar    $0x8,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x8(%rdx)
  mov    %edi,%esi
  sar    $0xc,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0xc(%rdx)
  mov    %edi,%esi
  sar    $0x10,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x10(%rdx)
  mov    %edi,%esi
  sar    $0x14,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x14(%rdx)
  mov    %edi,%esi
  sar    $0x18,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x18(%rdx)
  mov    %edi,%esi
  shr    $0x1c,%esi
  add    %eax,%esi
  mov    %esi,0x1c(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x24,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x20(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x28,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x24(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x2c,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x28(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x30,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x2c(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x34,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x30(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x38,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x34(%rdx)
  mov    %edi,%esi
  sar    %cl,%esi
  mov    $0x3c,%ecx
  and    $0xf,%esi
  sar    %cl,%edi
  mov    $0x20,%ecx
  add    %eax,%esi
  add    %eax,%edi
  mov    %esi,0x38(%rdx)
  mov    %r10d,%esi
  and    $0xf,%esi
  mov    %edi,0x3c(%rdx)
  add    %eax,%esi
  mov    %esi,0x40(%rdx)
  mov    %r10d,%esi
  sar    $0x4,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x44(%rdx)
  mov    %r10d,%esi
  sar    $0x8,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x48(%rdx)
  mov    %r10d,%esi
  sar    $0xc,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x4c(%rdx)
  mov    %r10d,%esi
  sar    $0x10,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x50(%rdx)
  mov    %r10d,%esi
  sar    $0x14,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x54(%rdx)
  mov    %r10d,%esi
  sar    $0x18,%esi
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x58(%rdx)
  mov    %r10d,%esi
  shr    $0x1c,%esi
  add    %eax,%esi
  mov    %esi,0x5c(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x24,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x60(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x28,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x64(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x2c,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x68(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x30,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x6c(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x34,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x70(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x38,%ecx
  and    $0xf,%esi
  add    %eax,%esi
  mov    %esi,0x74(%rdx)
  mov    %r10d,%esi
  sar    %cl,%esi
  mov    $0x3c,%ecx
  sar    %cl,%r10d
  and    $0xf,%esi
  mov    %r10d,%ecx
  add    %eax,%esi
  add    %eax,%ecx
  mov    %esi,0x78(%rdx)
  mov    %ecx,0x7c(%rdx)
  subq   $0xffffffffffffff80,(%r8)
  ret
```

assistant: ```c
void unpackforblock4_64(const uint64_t base, const uint8_t **pw, uint64_t **pout) {
  const uint64_t *pw64 = *(const uint64_t **)pw;
  uint64_t *out = *pout;
  const uint64_t mask = (15ULL);
  uint64_t w0 = pw64[0];
  uint64_t w1 = pw64[1];
  *pw += 16;
  out[0] = base + ((w0)&mask);
  out[1] = base + ((w0 >> 4) & mask);
  out[2] = base + ((w0 >> 8) & mask);
  out[3] = base + ((w0 >> 12) & mask);
  out[4] = base + ((w0 >> 16) & mask);
  out[5] = base + ((w0 >> 20) & mask);
  out[6] = base + ((w0 >> 24) & mask);
  out[7] = base + ((w0 >> 28) & mask);
  out[8] = base + ((w0 >> 32) & mask);
  out[9] = base + ((w0 >> 36) & mask);
  out[10] = base + ((w0 >> 40) & mask);
  out[11] = base + ((w0 >> 44) & mask);
  out[12] = base + ((w0 >> 48) & mask);
  out[13] = base + ((w0 >> 52) & mask);
  out[14] = base + ((w0 >> 56) & mask);
  out[15] = base + (w0 >> 60);
  out[16] = base + ((w1)&mask);
  out[17] = base + ((w1 >> 4) & mask);
  out[18] = base + ((w1 >> 8) & mask);
  out[19] = base + ((w1 >> 12) & mask);
  out[20] = base + ((w1 >> 16) & mask);
  out[21] = base + ((w1 >> 20) & mask);
  out[22] = base + ((w1 >> 24) & mask);
  out[23] = base + ((w1 >> 28) & mask);
  out[24] = base + ((w1 >> 32) & mask);
  out[25] = base + ((w1 >> 36) & mask);
  out[26] = base + ((w1 >> 40) & mask);
  out[27] = base + ((w1 >> 44) & mask);
  out[28] = base + ((w1 >> 48) & mask);
  out[29] = base + ((w1 >> 52) & mask);
  out[30] = base + ((w1 >> 56) & mask);
  out[31] = base + (w1 >> 60);
  *pout += 32;
}
```