user: What is the c source code of the assembly code below?

```asm
<dstsub>:
  endbr64
  push   %r15
  mov    %edi,%r15d
  mov    %edx,%eax
  mov    %edx,%edi
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  mov    %r15d,%ebx
  sar    %ebx
  mov    %edx,-0x54(%rsp)
  cltd
  idiv   %r15d
  mov    %ebx,-0x58(%rsp)
  cmp    $0x3,%r15d
  jle    L37
  movslq %eax,%r11
  movslq %edi,%rdx
  lea    -0x1(%rbx),%r9d
  xor    %ebp,%ebp
  sub    %r11,%rdx
  lea    -0x1(%r9),%rdi
  mov    %r9d,-0x18(%rsp)
  lea    0x0(,%rdx,4),%r14
  mov    %rdx,-0x28(%rsp)
  mov    %eax,%edx
  mov    %rdi,%r8
  neg    %edx
  mov    %r11,-0x38(%rsp)
  movslq %edx,%r10
  movslq %r15d,%rdx
  lea    0x0(,%r10,4),%r12
  mov    %r10,-0x30(%rsp)
  mov    %rbp,%r10
  imul   %r12,%r8
  test   %eax,%eax
  cmovle %r8,%r10
  neg    %r9
  shl    $0x2,%rdx
  shl    $0x2,%r9
  mov    %rdx,-0x50(%rsp)
  add    %r14,%r10
  lea    (%r9,%rdx,1),%rbx
  lea    -0x4(%rsi,%rdx,1),%rdx
  add    %rcx,%r10
  test   %eax,%eax
  mov    %rdx,-0x40(%rsp)
  lea    (%rsi,%rbx,1),%r13
  cmovle %rbp,%r8
  add    %r14,%r8
  lea    (%r8,%rcx,1),%rdx
  mov    %rsi,%r8
  sub    %r9,%r8
  lea    0x0(,%r11,4),%r9
  mov    %rdx,-0x48(%rsp)
  lea    0x4(%rsi),%rdx
  imul   %r9,%rdi
  mov    %r8,-0x20(%rsp)
  test   %eax,%eax
  mov    %rbp,%r8
  cmovns %rdi,%r8
  mov    %r8,%r11
  add    %r9,%r11
  add    %rcx,%r11
  test   %eax,%eax
  cmovns %rbp,%rdi
  mov    -0x50(%rsp),%rbp
  lea    (%rsi,%rbp,1),%r8
  mov    -0x58(%rsp),%ebp
  add    %r9,%rdi
  add    %rcx,%rdi
  mov    %r8,-0x10(%rsp)
  shl    $0x2,%rbp
  cmp    %rbx,%rbp
  setle  %bl
  cmp    %r8,%rdx
  mov    -0x40(%rsp),%r8
  setae  %bpl
  or     %ebx,%ebp
  cmpl   $0x2,-0x58(%rsp)
  setne  %bl
  and    %ebx,%ebp
  cmp    %r8,-0x48(%rsp)
  seta   %bl
  cmp    %r10,%r13
  seta   -0x11(%rsp)
  movzbl -0x11(%rsp),%r8d
  or     %r8d,%ebx
  and    %ebp,%ebx
  cmp    %rdx,%r10
  mov    -0x20(%rsp),%rbp
  setb   %r10b
  cmp    %rbp,-0x48(%rsp)
  seta   %r8b
  or     %r8d,%r10d
  and    %ebx,%r10d
  cmp    %r11,%r13
  seta   %r8b
  cmp    %rdi,-0x40(%rsp)
  setb   %bl
  or     %ebx,%r8d
  test   %r8b,%r10b
  je     L74
  cmp    %r11,%rdx
  seta   %r8b
  cmp    %rdi,%rbp
  setb   %dil
  or     %r8b,%dil
  je     L74
  mov    -0x58(%rsp),%ebx
  lea    -0x2(%rbx),%edi
  cmp    $0x2,%edi
  jbe    L24
  mov    -0x38(%rsp),%r11
  lea    (%rcx,%r14,1),%rdi
  lea    (%rcx,%r9,1),%r8
  mov    %r9,%r13
  mov    -0x50(%rsp),%rbp
  mov    -0x18(%rsp),%r14d
  mov    %rdi,%r10
  neg    %r13
  mov    %r11,%rbx
  mov    %rdx,-0x48(%rsp)
  lea    -0x10(%rsi,%rbp,1),%r12
  shr    $0x2,%r14d
  shl    $0x4,%rbx
  lea    0x0(,%r11,8),%rbp
  lea    (%r8,%rbp,1),%r11
  sub    %rbp,%r10
  lea    -0x10(%r12),%rbp
  sub    $0x1,%r14d
  shl    $0x4,%r14
  mov    %rbp,%rdx
  sub    %r14,%rdx
  mov    %rdx,%r14
  mov    -0x48(%rsp),%rdx
  jmp    L116
  nopl   0x0(%rax)
L52:
  sub    $0x10,%rbp
L116:
  movss  (%r11,%r9,1),%xmm0
  movss  (%r11),%xmm1
  add    $0x10,%rdx
  add    %rbx,%r11
  movss  (%r8,%r9,1),%xmm2
  movss  (%rdi,%r13,1),%xmm3
  unpcklps %xmm0,%xmm1
  movss  (%r8),%xmm0
  movups -0x10(%rdx),%xmm4
  add    %rbx,%r8
  unpcklps %xmm2,%xmm0
  movss  (%r10),%xmm2
  movlhps %xmm1,%xmm0
  movss  (%r10,%r13,1),%xmm1
  sub    %rbx,%r10
  unpcklps %xmm1,%xmm2
  movss  (%rdi),%xmm1
  sub    %rbx,%rdi
  unpcklps %xmm3,%xmm1
  movaps %xmm0,%xmm3
  movlhps %xmm2,%xmm1
  movups (%r12),%xmm2
  addps  %xmm1,%xmm0
  subps  %xmm1,%xmm3
  shufps $0x1b,%xmm2,%xmm2
  movaps %xmm3,%xmm1
  movaps %xmm0,%xmm5
  mulps  %xmm2,%xmm1
  mulps  %xmm4,%xmm5
  mulps  %xmm2,%xmm0
  mulps  %xmm4,%xmm3
  addps  %xmm5,%xmm1
  subps  %xmm3,%xmm0
  shufps $0x1b,%xmm1,%xmm1
  movups %xmm1,(%r12)
  mov    %rbp,%r12
  movups %xmm0,-0x10(%rdx)
  cmp    %r14,%rbp
  jne    L52
  mov    -0x18(%rsp),%ebx
  mov    %eax,%edi
  mov    %ebx,%r8d
  and    $0xfffffffc,%r8d
  imul   %r8d,%edi
  lea    0x1(%r8),%edx
  cmp    %r8d,%ebx
  je     L37
  mov    -0x58(%rsp),%r10d
  sub    %r8d,%r10d
  lea    -0x1(%r10),%ebp
  cmp    $0x2,%r10d
  je     L117
L108:
  lea    0x1(%r8),%rbx
  mov    %r9,%r10
  mov    -0x30(%rsp),%r11
  mov    -0x50(%rsp),%r14
  imul   %rbx,%r10
  lea    (%rsi,%rbx,4),%rbx
  imul   %r8,%r11
  neg    %r8
  add    -0x28(%rsp),%r11
  movq   (%rbx),%xmm4
  lea    -0x8(%r14,%r8,4),%r8
  mov    -0x38(%rsp),%r14
  lea    (%rcx,%r11,4),%r11
  add    %rcx,%r10
  add    %rsi,%r8
  movss  (%r10,%r14,4),%xmm1
  movss  (%r10),%xmm0
  mov    %r11,%r10
  sub    %r9,%r10
  movq   (%r8),%xmm3
  mov    %eax,%r9d
  movss  (%r10),%xmm2
  unpcklps %xmm1,%xmm0
  movss  (%r11),%xmm1
  shufps $0xe1,%xmm3,%xmm3
  unpcklps %xmm2,%xmm1
  movaps %xmm0,%xmm2
  subps  %xmm1,%xmm2
  addps  %xmm1,%xmm0
  movaps %xmm2,%xmm1
  movaps %xmm0,%xmm5
  mulps  %xmm3,%xmm1
  mulps  %xmm4,%xmm5
  mulps  %xmm3,%xmm0
  mulps  %xmm4,%xmm2
  addps  %xmm5,%xmm1
  subps  %xmm2,%xmm0
  shufps $0xe1,%xmm1,%xmm1
  movlps %xmm1,(%r8)
  mov    %ebp,%r8d
  and    $0xfffffffe,%r8d
  movlps %xmm0,(%rbx)
  imul   %r8d,%r9d
  add    %r8d,%edx
  add    %r9d,%edi
  cmp    %r8d,%ebp
  je     L37
L117:
  add    %eax,%edi
  movslq %edi,%rax
  movss  (%rcx,%rax,4),%xmm0
  mov    -0x54(%rsp),%eax
  sub    %edi,%eax
  movaps %xmm0,%xmm1
  cltq
  movss  (%rcx,%rax,4),%xmm2
  mov    %r15d,%eax
  sub    %edx,%eax
  movslq %edx,%rdx
  addss  %xmm2,%xmm0
  subss  %xmm2,%xmm1
  cltq
  lea    (%rsi,%rax,4),%rdi
  lea    (%rsi,%rdx,4),%rax
  movss  (%rdi),%xmm4
  movss  (%rax),%xmm3
  movaps %xmm1,%xmm2
  movaps %xmm0,%xmm5
  mulss  %xmm4,%xmm2
  mulss  %xmm3,%xmm5
  mulss  %xmm4,%xmm0
  mulss  %xmm3,%xmm1
  addss  %xmm5,%xmm2
  subss  %xmm1,%xmm0
  movss  %xmm2,(%rdi)
  movss  %xmm0,(%rax)
L37:
  movslq -0x58(%rsp),%rax
  lea    (%rsi,%rax,4),%rax
  movss  (%rax),%xmm0
  mulss  (%rcx),%xmm0
  movss  %xmm0,(%rax)
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopw   0x0(%rax,%rax,1)
L74:
  mov    -0x58(%rsp),%ebx
  mov    -0x10(%rsp),%rax
  lea    (%rcx,%r9,1),%r8
  lea    (%rcx,%r14,1),%rdi
  lea    -0x2(%rbx),%r10d
  lea    0x8(%rsi,%r10,4),%r10
  nopw   0x0(%rax,%rax,1)
L75:
  movss  (%rdi),%xmm2
  movss  (%r8),%xmm0
  add    $0x4,%rdx
  add    %r9,%r8
  movss  -0x4(%rax),%xmm4
  movss  -0x4(%rdx),%xmm3
  add    %r12,%rdi
  sub    $0x4,%rax
  movaps %xmm0,%xmm1
  addss  %xmm2,%xmm0
  subss  %xmm2,%xmm1
  movaps %xmm0,%xmm5
  mulss  %xmm3,%xmm5
  movaps %xmm1,%xmm2
  mulss  %xmm4,%xmm2
  mulss  %xmm4,%xmm0
  mulss  %xmm3,%xmm1
  addss  %xmm5,%xmm2
  subss  %xmm1,%xmm0
  movss  %xmm2,(%rax)
  movss  %xmm0,-0x4(%rdx)
  cmp    %rdx,%r10
  jne    L75
  jmp    L37
L24:
  mov    -0x18(%rsp),%ebp
  xor    %r8d,%r8d
  xor    %edi,%edi
  mov    $0x1,%edx
  jmp    L108
```

assistant: ```c
void dstsub(int n, float *a, int nc, float *c) {
  int j, k, kk, ks, m;
  float wkr, wki, xr;
  m = n >> 1;
  ks = nc / n;
  kk = 0;
  for (j = 1; j < m; j++) {
    k = n - j;
    kk += ks;
    wkr = c[kk] - c[nc - kk];
    wki = c[kk] + c[nc - kk];
    xr = wki * a[k] - wkr * a[j];
    a[k] = wkr * a[k] + wki * a[j];
    a[j] = xr;
  }
  a[m] *= c[0];
}
```