user: 提供的汇编代码用C语言表示会是什么样子:

```asm
<dmatvec>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  mov    %edi,-0x18(%rsp)
  mov    %esi,%ebp
  mov    %edx,-0x24(%rsp)
  mov    %rcx,%r13
  mov    %r8,-0x20(%rsp)
  cmp    $0x7,%edx
  jle    L31
  mov    %edx,%ebx
  movslq %edi,%rax
  lea    0x0(,%rax,8),%r11
  mov    %rax,%rsi
  shl    $0x6,%rsi
  mov    %rsi,-0x48(%rsp)
  mov    %r8,%rcx
  lea    (%rax,%rax,1),%rdx
  lea    (%rdx,%rax,1),%rsi
  lea    0x0(%r13,%rsi,8),%r15
  mov    %rsi,%rdx
  shl    $0x4,%rdx
  mov    %rdx,-0x30(%rsp)
  mov    %r11,%rsi
  add    %rdx,%rsi
  add    %r13,%rsi
  lea    -0x8(%rbx),%edx
  shr    $0x3,%edx
  mov    %edx,-0x14(%rsp)
  mov    %edx,%ebx
  mov    %rbx,-0x10(%rsp)
  mov    %rbx,%rdx
  shl    $0x6,%rdx
  lea    0x40(%r8,%rdx,1),%rbx
  mov    %rbx,-0x40(%rsp)
  shl    $0x4,%rax
  mov    %rax,-0x38(%rsp)
  mov    %r13,%rdx
  mov    %ebp,%r14d
  mov    %r13,-0x8(%rsp)
  mov    %r11,%r13
L106:
  lea    0x0(%r13,%rdx,1),%r10
  mov    -0x38(%rsp),%rax
  lea    (%rdx,%rax,1),%r11
  mov    %r15,%r8
  lea    0x0(%r13,%r15,1),%rdi
  lea    0x0(%r13,%rdi,1),%rbx
  mov    -0x30(%rsp),%rax
  lea    (%rdx,%rax,1),%r12
  movsd  (%rcx),%xmm1
  movsd  0x8(%rcx),%xmm2
  movsd  0x10(%rcx),%xmm3
  movsd  0x18(%rcx),%xmm4
  movsd  0x20(%rcx),%xmm5
  movsd  0x28(%rcx),%xmm6
  movsd  0x30(%rcx),%xmm7
  movsd  0x38(%rcx),%xmm8
  test   %ebp,%ebp
  jle    L96
  mov    $0x0,%eax
L27:
  movapd %xmm1,%xmm0
  mulsd  (%rdx,%rax,8),%xmm0
  movapd %xmm2,%xmm9
  mulsd  (%r10,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm3,%xmm9
  mulsd  (%r11,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm4,%xmm9
  mulsd  (%r8,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm5,%xmm9
  mulsd  (%rdi,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm6,%xmm9
  mulsd  (%rbx,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm7,%xmm9
  mulsd  (%r12,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  movapd %xmm8,%xmm9
  mulsd  (%rsi,%rax,8),%xmm9
  addsd  %xmm9,%xmm0
  addsd  (%r9,%rax,8),%xmm0
  movsd  %xmm0,(%r9,%rax,8)
  add    $0x1,%rax
  cmp    %r14,%rax
  jne    L27
L96:
  mov    -0x48(%rsp),%rax
  add    %rax,%rdx
  add    $0x40,%rcx
  add    %rax,%r15
  add    %rax,%rsi
  cmp    -0x40(%rsp),%rcx
  jne    L106
  mov    -0x8(%rsp),%r13
  mov    -0x14(%rsp),%eax
  lea    0x8(,%rax,8),%ebx
  mov    -0x10(%rsp),%rax
  add    $0x1,%rax
  imul   -0x48(%rsp),%rax
  add    %rax,%r13
L25:
  mov    -0x24(%rsp),%edi
  lea    -0x3(%rdi),%eax
  cmp    %ebx,%eax
  jle    L40
  mov    -0x18(%rsp),%eax
  movslq %eax,%r12
  lea    0x0(,%r12,8),%r15
  lea    0x0(,%rax,4),%r11d
  movslq %r11d,%r11
  shl    $0x3,%r11
  movslq %ebx,%rax
  mov    -0x20(%rsp),%rsi
  lea    (%rsi,%rax,8),%r10
  lea    (%r12,%r12,2),%rdx
  lea    0x0(%r13,%rdx,8),%rcx
  lea    -0x4(%rdi),%edx
  sub    %ebx,%edx
  shr    $0x2,%edx
  mov    %edx,-0x48(%rsp)
  mov    %edx,%edi
  mov    %rdi,-0x40(%rsp)
  lea    (%rax,%rdi,4),%rax
  lea    0x20(%rsi,%rax,8),%r14
  shl    $0x4,%r12
  mov    %r13,%rdx
  mov    %ebp,%r8d
L56:
  lea    (%r15,%rdx,1),%rsi
  lea    (%rdx,%r12,1),%rdi
  movsd  (%r10),%xmm2
  movsd  0x8(%r10),%xmm3
  movsd  0x10(%r10),%xmm4
  movsd  0x18(%r10),%xmm5
  test   %ebp,%ebp
  jle    L72
  mov    $0x0,%eax
L19:
  movapd %xmm2,%xmm0
  mulsd  (%rdx,%rax,8),%xmm0
  movapd %xmm3,%xmm1
  mulsd  (%rsi,%rax,8),%xmm1
  addsd  %xmm1,%xmm0
  movapd %xmm4,%xmm1
  mulsd  (%rdi,%rax,8),%xmm1
  addsd  %xmm1,%xmm0
  movapd %xmm5,%xmm1
  mulsd  (%rcx,%rax,8),%xmm1
  addsd  %xmm1,%xmm0
  addsd  (%r9,%rax,8),%xmm0
  movsd  %xmm0,(%r9,%rax,8)
  add    $0x1,%rax
  cmp    %r8,%rax
  jne    L19
L72:
  add    %r11,%rdx
  add    $0x20,%r10
  add    %r11,%rcx
  cmp    %r14,%r10
  jne    L56
  mov    -0x48(%rsp),%eax
  lea    0x4(%rbx,%rax,4),%ebx
  mov    -0x40(%rsp),%rax
  add    $0x1,%rax
  imul   %r11,%rax
  add    %rax,%r13
L40:
  mov    -0x24(%rsp),%esi
  cmp    %ebx,%esi
  jle    L11
  movslq -0x18(%rsp),%rcx
  shl    $0x3,%rcx
  movslq %ebx,%rbx
  mov    %ebp,%edx
  mov    -0x20(%rsp),%rdi
L64:
  movsd  (%rdi,%rbx,8),%xmm1
  test   %ebp,%ebp
  jle    L99
  mov    $0x0,%eax
L75:
  movapd %xmm1,%xmm0
  mulsd  0x0(%r13,%rax,8),%xmm0
  addsd  (%r9,%rax,8),%xmm0
  movsd  %xmm0,(%r9,%rax,8)
  add    $0x1,%rax
  cmp    %rdx,%rax
  jne    L75
L99:
  add    %rcx,%r13
  add    $0x1,%rbx
  cmp    %ebx,%esi
  jg     L64
L11:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L31:
  mov    $0x0,%ebx
  jmp    L25
```

assistant: ```c
void dmatvec(ldm, nrow, ncol, M, vec, Mxvec) int ldm;
int nrow;
int ncol;
double *M;
double *vec;
double *Mxvec;
{
  register double vi0, vi1, vi2, vi3, vi4, vi5, vi6, vi7;
  register double *Mki0, *Mki1, *Mki2, *Mki3, *Mki4, *Mki5, *Mki6, *Mki7;
  register int firstcol = 0;
  double *M0;
  int k;
  M0 = &M[0];
  while (firstcol < ncol - 7) {
    Mki0 = M0;
    Mki1 = Mki0 + ldm;
    Mki2 = Mki1 + ldm;
    Mki3 = Mki2 + ldm;
    Mki4 = Mki3 + ldm;
    Mki5 = Mki4 + ldm;
    Mki6 = Mki5 + ldm;
    Mki7 = Mki6 + ldm;
    vi0 = vec[firstcol++];
    vi1 = vec[firstcol++];
    vi2 = vec[firstcol++];
    vi3 = vec[firstcol++];
    vi4 = vec[firstcol++];
    vi5 = vec[firstcol++];
    vi6 = vec[firstcol++];
    vi7 = vec[firstcol++];
    for (k = 0; k < nrow; k++)
      Mxvec[k] += vi0 * Mki0[k] + vi1 * Mki1[k] + vi2 * Mki2[k] + vi3 * Mki3[k] + vi4 * Mki4[k] + vi5 * Mki5[k] + vi6 * Mki6[k] + vi7 * Mki7[k];
    M0 += 8 * ldm;
  }
  while (firstcol < ncol - 3) {
    Mki0 = M0;
    Mki1 = Mki0 + ldm;
    Mki2 = Mki1 + ldm;
    Mki3 = Mki2 + ldm;
    vi0 = vec[firstcol++];
    vi1 = vec[firstcol++];
    vi2 = vec[firstcol++];
    vi3 = vec[firstcol++];
    for (k = 0; k < nrow; k++)
      Mxvec[k] += vi0 * Mki0[k] + vi1 * Mki1[k] + vi2 * Mki2[k] + vi3 * Mki3[k];
    M0 += 4 * ldm;
  }
  while (firstcol < ncol) {
    Mki0 = M0;
    vi0 = vec[firstcol++];
    for (k = 0; k < nrow; k++)
      Mxvec[k] += vi0 * Mki0[k];
    M0 += ldm;
  }
}
```