user: 请显示与下面列出的汇编代码相匹配的C语言实现:

```asm
<FFTNXCorr>:
  endbr64
  push   %r15
  push   %r14
  mov    %rdx,%r14
  push   %r13
  push   %r12
  push   %rbp
  mov    %rcx,%rbp
  push   %rbx
  mov    %rsi,%rbx
  sub    $0x28,%rsp
  cmp    %rsi,%rcx
  mov    %rdi,0x18(%rsp)
  mov    %rsi,%rdi
  cmovae %rcx,%rdi
  mov    %r8,0x10(%rsp)
  call   <nextpow2@plt>
  lea    0x8(,%rax,8),%r12d
  mov    %rax,%r13
  mov    %r12d,%edi
  call   <safe_malloc@plt>
  mov    %r12d,%edi
  mov    %rax,%r15
  call   <safe_malloc@plt>
  mov    0x18(%rsp),%r10
  lea    -0x1(%rbx),%rsi
  mov    %rax,%r12
  mov    %rsi,0x8(%rsp)
  mov    %rsi,%rax
  lea    (%r10,%rbx,4),%rcx
  add    %r15,%rcx
  test   %rsi,%rsi
  js     L86
  nopw   0x0(%rax,%rax,1)
L46:
  add    $0x4,%r10
  mov    %rcx,%rdx
  movss  -0x4(%r10),%xmm0
  sub    %r10,%rdx
  movss  %xmm0,(%rdx)
  sub    $0x1,%rax
  jae    L46
L86:
  lea    0x0(%r13,%r13,1),%rcx
  cmp    %rcx,%rbx
  jge    L2
  mov    %rcx,%rdx
  lea    (%r15,%rbx,4),%rdi
  xor    %esi,%esi
  mov    %rcx,0x18(%rsp)
  sub    %rbx,%rdx
  shl    $0x2,%rdx
  call   <memset@plt>
  mov    0x18(%rsp),%rcx
L2:
  lea    0x0(%r13,%r13,1),%ebx
  mov    %r15,%rdi
  mov    %rcx,0x18(%rsp)
  sub    %r12,%r14
  mov    %ebx,%esi
  call   <RealFFT@plt>
  test   %rbp,%rbp
  mov    0x18(%rsp),%rcx
  mov    %r12,%rax
  lea    (%r12,%rbp,4),%rdx
  jle    L67
  nopl   0x0(%rax,%rax,1)
L28:
  movss  (%r14,%rax,1),%xmm0
  add    $0x4,%rax
  movss  %xmm0,-0x4(%rax)
  cmp    %rax,%rdx
  jne    L28
L67:
  cmp    %rbp,%rcx
  jle    L43
  sub    %rbp,%rcx
  lea    (%r12,%rbp,4),%rdi
  xor    %esi,%esi
  lea    0x0(,%rcx,4),%rdx
  call   <memset@plt>
L43:
  mov    %ebx,%esi
  mov    %r12,%rdi
  call   <RealFFT@plt>
  test   %r13,%r13
  js     L11
  lea    0x4(%r12),%rcx
  mov    %r12,%rsi
  lea    0x8(%r15,%r13,8),%rdi
  mov    %r15,%rax
  sub    %r15,%rsi
  sub    %r15,%rcx
  nopl   0x0(%rax)
L0:
  lea    (%rsi,%rax,1),%rdx
  lea    (%rcx,%rax,1),%r10
  movss  (%rax),%xmm0
  movss  0x4(%rax),%xmm1
  movss  (%rdx),%xmm2
  movss  (%r10),%xmm3
  add    $0x8,%rax
  mulss  %xmm0,%xmm2
  mulss  %xmm1,%xmm3
  subss  %xmm3,%xmm2
  movss  %xmm2,-0x8(%rax)
  mulss  (%r10),%xmm0
  mulss  (%rdx),%xmm1
  addss  %xmm1,%xmm0
  movss  %xmm0,-0x4(%rax)
  cmp    %rdi,%rax
  jne    L0
L11:
  mov    %ebx,%esi
  mov    %r15,%rdi
  call   <RealIFFT@plt>
  mov    0x8(%rsp),%r13
  mov    0x10(%rsp),%rbx
  mov    %r15,%rax
  add    %rbp,%r13
  sub    %r15,%rbx
  lea    (%r15,%r13,4),%rdx
  test   %r13,%r13
  jle    L41
  nopl   0x0(%rax)
L52:
  movss  (%rax),%xmm0
  movss  %xmm0,(%rbx,%rax,1)
  add    $0x4,%rax
  cmp    %rax,%rdx
  jne    L52
L41:
  mov    %r15,%rdi
  call   <safe_free@plt>
  mov    %r12,%rdi
  call   <safe_free@plt>
  add    $0x28,%rsp
  mov    %r13,%rax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
unsigned long FFTNXCorr(float *x1, unsigned long n1, float *x2, unsigned long n2, float *y) {
  register float r1, i1;
  float *tmp1;
  float *tmp2;
  long C, D, Nx, Ny;
  Nx = nextpow2((((n1) > (n2)) ? (n1) : (n2)));
  tmp1 = (float *)safe_malloc(sizeof(float) * (2 * Nx + 2));
  tmp2 = (float *)safe_malloc(sizeof(float) * (2 * Nx + 2));
  for (C = n1 - 1; C >= 0; C--) {
    tmp1[C] = *(x1++);
  }
  for (C = n1; C < 2 * Nx; C++)
    tmp1[C] = 0.0;
  RealFFT(tmp1, 2 * Nx);
  for (C = 0; C < (long)n2; C++) {
    tmp2[C] = x2[C];
  }
  for (C = n2; C < 2 * Nx; C++)
    tmp2[C] = 0.0;
  RealFFT(tmp2, 2 * Nx);
  for (C = 0; C <= Nx; C++) {
    D = C << 1;
    r1 = tmp1[D];
    i1 = tmp1[1 + D];
    tmp1[D] = r1 * tmp2[D] - i1 * tmp2[1 + D];
    tmp1[1 + D] = r1 * tmp2[1 + D] + i1 * tmp2[D];
  }
  RealIFFT(tmp1, 2 * Nx);
  Ny = n1 + n2 - 1;
  for (C = 0; C < Ny; C++)
    y[C] = tmp1[C];
  safe_free(tmp1);
  safe_free(tmp2);
  return Ny;
}
```