user: 这段汇编代码用C语言表示是什么样的:

```asm
<jpegdct>:
  endbr64
  push   %r15
  mov    %rsi,%rdx
  mov    $0x8,%esi
  mov    $0x2,%r15d
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  movl   $0x0,-0x8(%rsp)
  movq   $0x6,-0x20(%rsp)
  mov    %si,-0x4(%rsp)
  mov    %rdi,-0x10(%rsp)
L41:
  mov    -0x20(%rsp),%rdi
  lea    0x0(,%r15,8),%rcx
  sub    %r15,%rcx
  lea    (%rdi,%rdi,1),%rax
  mov    %rcx,-0x30(%rsp)
  mov    %rax,-0x38(%rsp)
  lea    (%r15,%r15,1),%rax
  mov    %rax,-0x40(%rsp)
  lea    0x0(,%r15,4),%rax
  lea    (%rax,%r15,1),%rsi
  mov    %rsi,-0x28(%rsp)
  mov    $0x12,%esi
  sub    %r15,%rsi
  mov    %rsi,-0x18(%rsp)
  mov    -0x8(%rsp),%esi
  add    $0xd,%esi
  cmpw   $0x1,-0x4(%rsp)
  jne    L39
  mov    $0x8,%ebp
  mov    %rax,-0x20(%rsp)
  mov    -0x10(%rsp),%rax
  mov    %bp,-0x4(%rsp)
  mov    %rdi,%rbp
  cs nopw 0x0(%rax,%rax,1)
L17:
  mov    -0x30(%rsp),%rbx
  movswl (%rax),%edi
  mov    -0x38(%rsp),%r14
  mov    -0x40(%rsp),%r9
  movswl (%rax,%rbx,1),%ecx
  mov    -0x28(%rsp),%r10
  movswl (%rax,%r15,1),%r8d
  movswl (%rax,%r9,1),%r9d
  movswl (%rax,%r10,1),%r10d
  lea    (%rcx,%rdi,1),%ebx
  mov    -0x20(%rsp),%r12
  sub    %ecx,%edi
  movswl (%rax,%r14,1),%ecx
  movslq %ebx,%rbx
  movswl (%rax,%r12,1),%r12d
  lea    (%rcx,%r8,1),%r11d
  sub    %ecx,%r8d
  lea    (%r10,%r9,1),%ecx
  sub    %r10d,%r9d
  movswl (%rax,%rbp,1),%r10d
  movslq %ecx,%rcx
  movslq %r11d,%r11
  lea    (%rcx,%r11,1),%r14
  sub    %rcx,%r11
  movzbl -0x8(%rsp),%ecx
  lea    (%r12,%r10,1),%r13d
  sub    %r12d,%r10d
  movslq %r13d,%r13
  lea    0x0(%r13,%rbx,1),%r12
  sub    %r13,%rbx
  lea    (%r14,%r12,1),%r13
  sub    %r14,%r12
  mov    -0x38(%rsp),%r14
  sar    %cl,%r13
  sar    %cl,%r12
  mov    -0x20(%rsp),%rcx
  mov    %r13w,(%rax)
  mov    -0x40(%rsp),%r13
  mov    %r12w,(%rax,%rcx,1)
  lea    (%rbx,%r11,1),%ecx
  movswl 0x14(%rdx),%r12d
  movswl %cx,%ecx
  imul   %ecx,%r12d
  movswq 0x12(%rdx),%rcx
  imul   %rcx,%rbx
  mov    %esi,%ecx
  sar    %cl,%rbx
  add    %r12d,%ebx
  mov    %bx,(%rax,%r13,1)
  movswq 0x16(%rdx),%rcx
  imul   %rcx,%r11
  mov    %esi,%ecx
  sar    %cl,%r11
  lea    (%r9,%r8,1),%ecx
  add    %r11d,%r12d
  movswl %cx,%ecx
  movslq %edi,%r11
  mov    %r12w,(%rax,%r14,1)
  movswl (%rdx),%r13d
  movslq %r10d,%r14
  movswl 0x10(%rdx),%ebx
  movswl 0x4(%rdx),%r12d
  imul   %ecx,%r13d
  movslq %r8d,%rcx
  add    %rcx,%r14
  movslq %r9d,%rcx
  add    %r11,%rcx
  lea    (%rcx,%r14,1),%r11d
  movswl %cx,%ecx
  movswl %r14w,%r14d
  movswl %r11w,%r11d
  imul   %r11d,%ebx
  movswl 0x6(%rdx),%r11d
  imul   %ecx,%r11d
  lea    (%r10,%rdi,1),%ecx
  movswl %cx,%ecx
  imul   0x8(%rdx),%r10w
  movslq %ebx,%rbx
  imul   %ecx,%r12d
  movswl 0x2(%rdx),%ecx
  movslq %r11d,%r11
  imul   %r14d,%ecx
  add    %rbx,%r11
  add    %r12d,%r10d
  movslq %ecx,%rcx
  add    %rcx,%rbx
  mov    %esi,%ecx
  add    %ebx,%r10d
  movswl %r10w,%r10d
  sar    %cl,%r10d
  mov    -0x30(%rsp),%rcx
  mov    %r10w,(%rax,%rcx,1)
  imul   0xc(%rdx),%r9w
  mov    %esi,%ecx
  mov    -0x28(%rsp),%r10
  add    %r13d,%r9d
  add    %r11d,%r9d
  movswl %r9w,%r9d
  sar    %cl,%r9d
  mov    %r9w,(%rax,%r10,1)
  imul   0xa(%rdx),%r8w
  add    %r13d,%r8d
  add    %ebx,%r8d
  movswl %r8w,%r8d
  sar    %cl,%r8d
  mov    %r8w,(%rax,%rbp,1)
  imul   0xe(%rdx),%di
  add    %r12d,%edi
  add    %r11d,%edi
  movswl %di,%edi
  sar    %cl,%edi
  mov    %di,(%rax,%r15,1)
  add    -0x18(%rsp),%rax
  subw   $0x1,-0x4(%rsp)
  jne    L17
L34:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L39:
  mov    $0x8,%ecx
  mov    -0x10(%rsp),%rdi
  mov    %cx,-0x2(%rsp)
  nopw   0x0(%rax,%rax,1)
L19:
  mov    -0x30(%rsp),%rbx
  movswl (%rdi),%r8d
  mov    -0x38(%rsp),%r14
  mov    -0x40(%rsp),%r10
  movswl (%rdi,%rbx,1),%ecx
  mov    -0x28(%rsp),%r11
  movswl (%rdi,%r15,1),%r9d
  movswl (%rdi,%r10,1),%r10d
  movswl (%rdi,%r11,1),%r11d
  mov    -0x20(%rsp),%r12
  lea    (%r8,%rcx,1),%ebp
  sub    %ecx,%r8d
  movswl (%rdi,%r14,1),%ecx
  movslq %ebp,%rbp
  lea    (%r9,%rcx,1),%ebx
  sub    %ecx,%r9d
  lea    (%r10,%r11,1),%ecx
  sub    %r11d,%r10d
  movswl (%rdi,%r12,1),%r11d
  movswl (%rdi,%rax,1),%r12d
  movslq %ecx,%rcx
  movslq %ebx,%rbx
  lea    (%rbx,%rcx,1),%r14
  sub    %rcx,%rbx
  movzbl -0x8(%rsp),%ecx
  lea    (%r11,%r12,1),%r13d
  sub    %r12d,%r11d
  movslq %r13d,%r13
  lea    0x0(%rbp,%r13,1),%r12
  sub    %r13,%rbp
  lea    (%r12,%r14,1),%r13
  sub    %r14,%r12
  mov    -0x38(%rsp),%r14
  sar    %cl,%r13
  sar    %cl,%r12
  mov    %r13w,(%rdi)
  mov    -0x40(%rsp),%r13
  mov    %r12w,(%rdi,%rax,1)
  lea    (%rbx,%rbp,1),%r12d
  movswl 0x14(%rdx),%ecx
  movswl %r12w,%r12d
  imul   %ecx,%r12d
  movswq 0x12(%rdx),%rcx
  imul   %rcx,%rbp
  mov    %esi,%ecx
  sar    %cl,%rbp
  add    %r12d,%ebp
  mov    %bp,(%rdi,%r13,1)
  movswq 0x16(%rdx),%rcx
  lea    (%r9,%r10,1),%r13d
  movswl %r13w,%r13d
  imul   %rcx,%rbx
  mov    %esi,%ecx
  sar    %cl,%rbx
  add    %ebx,%r12d
  movslq %r10d,%rbx
  mov    %r12w,(%rdi,%r14,1)
  movswl (%rdx),%ecx
  movslq %r9d,%r14
  lea    (%r8,%r11,1),%r12d
  movswl %r12w,%r12d
  imul   %ecx,%r13d
  movslq %r11d,%rcx
  add    %rcx,%r14
  imul   0x8(%rdx),%r11w
  movslq %r8d,%rcx
  add    %rbx,%rcx
  movswl 0x10(%rdx),%ebx
  lea    (%r14,%rcx,1),%ebp
  movswl %cx,%ecx
  movswl %r14w,%r14d
  movswl %bp,%ebp
  imul   %ebx,%ebp
  movswl 0x6(%rdx),%ebx
  imul   %ecx,%ebx
  movswl 0x4(%rdx),%ecx
  movslq %ebp,%rbp
  imul   %ecx,%r12d
  movswl 0x2(%rdx),%ecx
  movslq %ebx,%rbx
  imul   %r14d,%ecx
  add    %rbp,%rbx
  add    %r12d,%r11d
  movslq %ecx,%rcx
  add    %rcx,%rbp
  mov    %esi,%ecx
  add    %ebp,%r11d
  movswl %r11w,%r11d
  sar    %cl,%r11d
  mov    -0x30(%rsp),%rcx
  mov    %r11w,(%rdi,%rcx,1)
  imul   0xc(%rdx),%r10w
  mov    %esi,%ecx
  mov    -0x28(%rsp),%r11
  add    %r13d,%r10d
  add    %ebx,%r10d
  movswl %r10w,%r10d
  sar    %cl,%r10d
  mov    %r10w,(%rdi,%r11,1)
  imul   0xa(%rdx),%r9w
  add    %r13d,%r9d
  add    %ebp,%r9d
  movswl %r9w,%r9d
  sar    %cl,%r9d
  mov    -0x20(%rsp),%rcx
  mov    %r9w,(%rdi,%rcx,1)
  imul   0xe(%rdx),%r8w
  mov    %esi,%ecx
  add    %r12d,%r8d
  add    %ebx,%r8d
  movswl %r8w,%r8d
  sar    %cl,%r8d
  mov    %r8w,(%rdi,%r15,1)
  add    -0x18(%rsp),%rdi
  subw   $0x1,-0x2(%rsp)
  jne    L19
  mov    -0x10(%rsp),%rsi
  mov    %r15,%rcx
  addl   $0x3,-0x8(%rsp)
  add    $0xe,%r15
  subw   $0x7,-0x4(%rsp)
  neg    %rcx
  movzwl -0x4(%rsp),%eax
  lea    0x10(%rsi,%rcx,8),%rsi
  addq   $0x2a,-0x20(%rsp)
  mov    %rsi,-0x10(%rsp)
  cmp    $0xfffa,%ax
  jne    L41
  jmp    L34
```

assistant: ```c
void jpegdct(short *d, short *r) {
  long int t[12];
  short i, j, k, m, n, p;
  for (k = 1, m = 0, n = 13, p = 8; k <= 8; k += 7, m += 3, n += 3, p -= 7, d -= 64) {
    for (i = 0; i < 8; i++, d += p) {
      for (j = 0; j < 4; j++) {
        t[j] = d[k * j] + d[k * (7 - j)];
        t[7 - j] = d[k * j] - d[k * (7 - j)];
      }
      t[8] = t[0] + t[3];
      t[9] = t[0] - t[3];
      t[10] = t[1] + t[2];
      t[11] = t[1] - t[2];
      d[0] = (t[8] + t[10]) >> m;
      d[4 * k] = (t[8] - t[10]) >> m;
      t[8] = (short)(t[11] + t[9]) * r[10];
      d[2 * k] = t[8] + (short)((t[9] * r[9]) >> n);
      d[6 * k] = t[8] + (short)((t[11] * r[11]) >> n);
      t[0] = (short)(t[4] + t[7]) * r[2];
      t[1] = (short)(t[5] + t[6]) * r[0];
      t[2] = t[4] + t[6];
      t[3] = t[5] + t[7];
      t[8] = (short)(t[2] + t[3]) * r[8];
      t[2] = (short)t[2] * r[1] + t[8];
      t[3] = (short)t[3] * r[3] + t[8];
      d[7 * k] = (short)(t[4] * r[4] + t[0] + t[2]) >> n;
      d[5 * k] = (short)(t[5] * r[6] + t[1] + t[3]) >> n;
      d[3 * k] = (short)(t[6] * r[5] + t[1] + t[2]) >> n;
      d[1 * k] = (short)(t[7] * r[7] + t[0] + t[3]) >> n;
    }
  }
}
```