void mp_mul_rcsqu_nt_in(int n, double *a, int nc, double *c) {
  int j, k, kk, ks, m;
  double wkr, wki, xr, xi, yr, yi, ajr, aji, akr, aki;
  ks = (nc << 2) / n;
  kk = 0;
  m = n >> 1;
  for (j = 2; j < m; j += 2) {
    k = n - j;
    kk += ks;
    wkr = ((double)0.5) - c[nc - kk];
    wki = c[kk];
    xr = a[j];
    xi = a[j + 1];
    yr = a[k];
    yi = a[k + 1];
    ajr = xr * xr - xi * xi;
    aji = 2 * xr * xi;
    akr = yr * yr - yi * yi;
    aki = 2 * yr * yi;
    xr = ajr - akr;
    xi = aji + aki;
    yr = wkr * xr + wki * xi;
    yi = wkr * xi - wki * xr;
    a[j] = ajr - yr;
    a[j + 1] = aji - yi;
    a[k] = akr + yr;
    a[k + 1] = aki - yi;
  }
  xr = a[m];
  xi = a[m + 1];
  a[m] = xr * xr - xi * xi;
  a[m + 1] = 2 * xr * xi;
}


x86 assembly (clang, -O0):
<mp_mul_rcsqu_nt_in>:
push   %rbp
mov    %rsp,%rbp
push   %rax
mov    %edi,-0x4(%rbp)
mov    %rsi,-0x10(%rbp)
mov    %edx,-0x14(%rbp)
mov    %rcx,-0x20(%rbp)
mov    -0x14(%rbp),%eax
shl    $0x2,%eax
cltd
idivl  -0x4(%rbp)
mov    %eax,-0x30(%rbp)
movl   $0x0,-0x2c(%rbp)
mov    -0x4(%rbp),%eax
sar    $0x1,%eax
mov    %eax,-0x34(%rbp)
movl   $0x2,-0x24(%rbp)
mov    -0x24(%rbp),%eax
cmp    -0x34(%rbp),%eax
jge    136a <mp_mul_rcsqu_nt_in+0x26a>
mov    -0x4(%rbp),%eax
sub    -0x24(%rbp),%eax
mov    %eax,-0x28(%rbp)
mov    -0x30(%rbp),%eax
add    -0x2c(%rbp),%eax
mov    %eax,-0x2c(%rbp)
mov    -0x20(%rbp),%rax
mov    -0x14(%rbp),%ecx
sub    -0x2c(%rbp),%ecx
movslq %ecx,%rcx
movsd  0xe9e(%rip),%xmm0
subsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x40(%rbp)
mov    -0x20(%rbp),%rax
movslq -0x2c(%rbp),%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x48(%rbp)
mov    -0x10(%rbp),%rax
movslq -0x24(%rbp),%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x50(%rbp)
mov    -0x10(%rbp),%rax
mov    -0x24(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x58(%rbp)
mov    -0x10(%rbp),%rax
movslq -0x28(%rbp),%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x60(%rbp)
mov    -0x10(%rbp),%rax
mov    -0x28(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x68(%rbp)
movsd  -0x50(%rbp),%xmm0
movsd  -0x50(%rbp),%xmm2
movsd  -0x58(%rbp),%xmm1
mulsd  -0x58(%rbp),%xmm1
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x70(%rbp)
movsd  0xde8(%rip),%xmm0
mulsd  -0x50(%rbp),%xmm0
mulsd  -0x58(%rbp),%xmm0
movsd  %xmm0,-0x78(%rbp)
movsd  -0x60(%rbp),%xmm0
movsd  -0x60(%rbp),%xmm2
movsd  -0x68(%rbp),%xmm1
mulsd  -0x68(%rbp),%xmm1
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x80(%rbp)
movsd  0xd99(%rip),%xmm0
mulsd  -0x60(%rbp),%xmm0
mulsd  -0x68(%rbp),%xmm0
movsd  %xmm0,-0x88(%rbp)
ff
movsd  -0x70(%rbp),%xmm0
subsd  -0x80(%rbp),%xmm0
movsd  %xmm0,-0x50(%rbp)
movsd  -0x78(%rbp),%xmm0
addsd  -0x88(%rbp),%xmm0
ff
movsd  %xmm0,-0x58(%rbp)
movsd  -0x40(%rbp),%xmm0
movsd  -0x50(%rbp),%xmm2
movsd  -0x48(%rbp),%xmm1
mulsd  -0x58(%rbp),%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x60(%rbp)
movsd  -0x40(%rbp),%xmm0
movsd  -0x58(%rbp),%xmm2
movsd  -0x48(%rbp),%xmm1
mulsd  -0x50(%rbp),%xmm1
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
movsd  %xmm0,-0x68(%rbp)
movsd  -0x70(%rbp),%xmm0
subsd  -0x60(%rbp),%xmm0
mov    -0x10(%rbp),%rax
movslq -0x24(%rbp),%rcx
movsd  %xmm0,(%rax,%rcx,8)
movsd  -0x78(%rbp),%xmm0
subsd  -0x68(%rbp),%xmm0
mov    -0x10(%rbp),%rax
mov    -0x24(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  %xmm0,(%rax,%rcx,8)
movsd  -0x80(%rbp),%xmm0
addsd  -0x60(%rbp),%xmm0
mov    -0x10(%rbp),%rax
movslq -0x28(%rbp),%rcx
movsd  %xmm0,(%rax,%rcx,8)
movsd  -0x88(%rbp),%xmm0
ff
subsd  -0x68(%rbp),%xmm0
mov    -0x10(%rbp),%rax
mov    -0x28(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  %xmm0,(%rax,%rcx,8)
mov    -0x24(%rbp),%eax
add    $0x2,%eax
mov    %eax,-0x24(%rbp)
jmp    1137 <mp_mul_rcsqu_nt_in+0x37>
mov    -0x10(%rbp),%rax
movslq -0x34(%rbp),%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x50(%rbp)
mov    -0x10(%rbp),%rax
mov    -0x34(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  (%rax,%rcx,8),%xmm0
movsd  %xmm0,-0x58(%rbp)
movsd  -0x50(%rbp),%xmm0
movsd  -0x50(%rbp),%xmm2
movsd  -0x58(%rbp),%xmm1
mulsd  -0x58(%rbp),%xmm1
movq   %xmm1,%rax
movabs $0x8000000000000000,%rcx
xor    %rcx,%rax
movq   %rax,%xmm1
mulsd  %xmm2,%xmm0
addsd  %xmm1,%xmm0
mov    -0x10(%rbp),%rax
movslq -0x34(%rbp),%rcx
movsd  %xmm0,(%rax,%rcx,8)
movsd  0xc25(%rip),%xmm0
mulsd  -0x50(%rbp),%xmm0
mulsd  -0x58(%rbp),%xmm0
mov    -0x10(%rbp),%rax
mov    -0x34(%rbp),%ecx
add    $0x1,%ecx
movslq %ecx,%rcx
movsd  %xmm0,(%rax,%rcx,8)
add    $0x8,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<mp_mul_rcsqu_nt_in>:
mov    %edi,%r10d
sar    %r10d
movslq %r10d,%r9
cmp    $0x5,%edi
jle    122d <mp_mul_rcsqu_nt_in+0x12d>
mov    %edx,%r8d
lea    0x0(,%r8,4),%eax
cltd
idiv   %edi
mov    %edi,%edx
movslq %r10d,%r10
movslq %eax,%r11
movslq %r8d,%rax
lea    (%rcx,%r11,8),%rdi
sub    %r11,%rax
shl    $0x3,%r11
lea    (%rcx,%rax,8),%rcx
mov    %r11,%r8
neg    %r8
lea    (%rsi,%rdx,8),%rdx
add    $0xfffffffffffffff8,%rdx
mov    $0x2,%eax
movsd  0xeaa(%rip),%xmm9
movapd 0xeb1(%rip),%xmm8
nop
movapd %xmm9,%xmm2
subsd  (%rcx),%xmm2
movsd  (%rsi,%rax,8),%xmm5
movsd  0x8(%rsi,%rax,8),%xmm6
movsd  -0x8(%rdx),%xmm3
movsd  (%rdx),%xmm7
movapd %xmm5,%xmm4
addsd  %xmm5,%xmm5
mulsd  %xmm6,%xmm5
mulsd  %xmm6,%xmm6
mulsd  %xmm4,%xmm4
subsd  %xmm6,%xmm4
unpcklpd %xmm5,%xmm4
movapd %xmm3,%xmm5
addsd  %xmm3,%xmm3
mulsd  %xmm7,%xmm3
mulsd  %xmm7,%xmm7
mulsd  %xmm5,%xmm5
subsd  %xmm7,%xmm5
movapd %xmm5,%xmm6
unpcklpd %xmm3,%xmm6
movapd %xmm4,%xmm7
subpd  %xmm6,%xmm7
addpd  %xmm4,%xmm6
movapd %xmm6,%xmm10
movsd  %xmm7,%xmm10
movsd  (%rdi),%xmm0
movapd %xmm0,%xmm1
xorpd  %xmm8,%xmm1
unpcklpd %xmm7,%xmm0
shufpd $0x1,%xmm1,%xmm6
mulpd  %xmm0,%xmm6
unpcklpd %xmm2,%xmm2
mulpd  %xmm10,%xmm2
addpd  %xmm6,%xmm2
subpd  %xmm2,%xmm4
movupd %xmm4,(%rsi,%rax,8)
addsd  %xmm2,%xmm5
movsd  %xmm5,-0x8(%rdx)
unpckhpd %xmm2,%xmm2
subsd  %xmm2,%xmm3
movsd  %xmm3,(%rdx)
add    $0x2,%rax
add    %r11,%rdi
add    %r8,%rcx
add    $0xfffffffffffffff0,%rdx
cmp    %r10,%rax
jl     1160 <mp_mul_rcsqu_nt_in+0x60>
jmp    1230 <mp_mul_rcsqu_nt_in+0x130>
mov    %r9,%r10
movsd  (%rsi,%r10,8),%xmm0
movsd  0x8(%rsi,%r9,8),%xmm1
movapd %xmm0,%xmm2
addsd  %xmm0,%xmm0
mulsd  %xmm1,%xmm0
mulsd  %xmm1,%xmm1
mulsd  %xmm2,%xmm2
subsd  %xmm1,%xmm2
movsd  %xmm2,(%rsi,%r10,8)
movsd  %xmm0,0x8(%rsi,%r9,8)
ret

LLVM IR (-O0):
define void @mp_mul_rcsqu_nt_in(i32 %0, double* %1, i32 %2, double* %3) {
%5 = alloca i32
%6 = alloca double*
%7 = alloca i32
%8 = alloca double*
%9 = alloca i32
%10 = alloca i32
%11 = alloca i32
%12 = alloca i32
%13 = alloca i32
%14 = alloca double
%15 = alloca double
%16 = alloca double
%17 = alloca double
%18 = alloca double
%19 = alloca double
%20 = alloca double
%21 = alloca double
%22 = alloca double
%23 = alloca double
store i32 %0, i32* %5
store double* %1, double** %6
store i32 %2, i32* %7
store double* %3, double** %8
%24 = load i32, i32* %7
%25 = shl i32 %24, 2
%26 = load i32, i32* %5
%27 = sdiv i32 %25, %26
store i32 %27, i32* %12
store i32 0, i32* %11
%28 = load i32, i32* %5
%29 = ashr i32 %28, 1
store i32 %29, i32* %13
store i32 2, i32* %9
br label %30
30: ; preds = %147, %4
%31 = load i32, i32* %9
%32 = load i32, i32* %13
%33 = icmp slt i32 %31, %32
br i1 %33, label %34, label %150
34: ; preds = %30
%35 = load i32, i32* %5
%36 = load i32, i32* %9
%37 = sub nsw i32 %35, %36
store i32 %37, i32* %10
%38 = load i32, i32* %12
%39 = load i32, i32* %11
%40 = add nsw i32 %39, %38
store i32 %40, i32* %11
%41 = load double*, double** %8
%42 = load i32, i32* %7
%43 = load i32, i32* %11
%44 = sub nsw i32 %42, %43
%45 = sext i32 %44 to i64
%46 = getelementptr inbounds double, double* %41, i64 %45
%47 = load double, double* %46
%48 = fsub double 5.000000e-01, %47
store double %48, double* %14
%49 = load double*, double** %8
%50 = load i32, i32* %11
%51 = sext i32 %50 to i64
%52 = getelementptr inbounds double, double* %49, i64 %51
%53 = load double, double* %52
store double %53, double* %15
%54 = load double*, double** %6
%55 = load i32, i32* %9
%56 = sext i32 %55 to i64
%57 = getelementptr inbounds double, double* %54, i64 %56
%58 = load double, double* %57
store double %58, double* %16
%59 = load double*, double** %6
%60 = load i32, i32* %9
%61 = add nsw i32 %60, 1
%62 = sext i32 %61 to i64
%63 = getelementptr inbounds double, double* %59, i64 %62
%64 = load double, double* %63
store double %64, double* %17
%65 = load double*, double** %6
%66 = load i32, i32* %10
%67 = sext i32 %66 to i64
%68 = getelementptr inbounds double, double* %65, i64 %67
%69 = load double, double* %68
store double %69, double* %18
%70 = load double*, double** %6
%71 = load i32, i32* %10
%72 = add nsw i32 %71, 1
%73 = sext i32 %72 to i64
%74 = getelementptr inbounds double, double* %70, i64 %73
%75 = load double, double* %74
store double %75, double* %19
%76 = load double, double* %16
%77 = load double, double* %16
%78 = load double, double* %17
%79 = load double, double* %17
%80 = fmul double %78, %79
%81 = fneg double %80
%82 = call double @llvm.fmuladd.f64(double %76, double %77, double %81)
store double %82, double* %20
%83 = load double, double* %16
%84 = fmul double 2.000000e+00, %83
%85 = load double, double* %17
%86 = fmul double %84, %85
store double %86, double* %21
%87 = load double, double* %18
%88 = load double, double* %18
%89 = load double, double* %19
%90 = load double, double* %19
%91 = fmul double %89, %90
%92 = fneg double %91
%93 = call double @llvm.fmuladd.f64(double %87, double %88, double %92)
store double %93, double* %22
%94 = load double, double* %18
%95 = fmul double 2.000000e+00, %94
%96 = load double, double* %19
%97 = fmul double %95, %96
store double %97, double* %23
%98 = load double, double* %20
%99 = load double, double* %22
%100 = fsub double %98, %99
store double %100, double* %16
%101 = load double, double* %21
%102 = load double, double* %23
%103 = fadd double %101, %102
store double %103, double* %17
%104 = load double, double* %14
%105 = load double, double* %16
%106 = load double, double* %15
%107 = load double, double* %17
%108 = fmul double %106, %107
%109 = call double @llvm.fmuladd.f64(double %104, double %105, double %108)
store double %109, double* %18
%110 = load double, double* %14
%111 = load double, double* %17
%112 = load double, double* %15
%113 = load double, double* %16
%114 = fmul double %112, %113
%115 = fneg double %114
%116 = call double @llvm.fmuladd.f64(double %110, double %111, double %115)
store double %116, double* %19
%117 = load double, double* %20
%118 = load double, double* %18
%119 = fsub double %117, %118
%120 = load double*, double** %6
%121 = load i32, i32* %9
%122 = sext i32 %121 to i64
%123 = getelementptr inbounds double, double* %120, i64 %122
store double %119, double* %123
%124 = load double, double* %21
%125 = load double, double* %19
%126 = fsub double %124, %125
%127 = load double*, double** %6
%128 = load i32, i32* %9
%129 = add nsw i32 %128, 1
%130 = sext i32 %129 to i64
%131 = getelementptr inbounds double, double* %127, i64 %130
store double %126, double* %131
%132 = load double, double* %22
%133 = load double, double* %18
%134 = fadd double %132, %133
%135 = load double*, double** %6
%136 = load i32, i32* %10
%137 = sext i32 %136 to i64
%138 = getelementptr inbounds double, double* %135, i64 %137
store double %134, double* %138
%139 = load double, double* %23
%140 = load double, double* %19
%141 = fsub double %139, %140
%142 = load double*, double** %6
%143 = load i32, i32* %10
%144 = add nsw i32 %143, 1
%145 = sext i32 %144 to i64
%146 = getelementptr inbounds double, double* %142, i64 %145
store double %141, double* %146
br label %147
147: ; preds = %34
%148 = load i32, i32* %9
%149 = add nsw i32 %148, 2
store i32 %149, i32* %9
br label %30
150: ; preds = %30
%151 = load double*, double** %6
%152 = load i32, i32* %13
%153 = sext i32 %152 to i64
%154 = getelementptr inbounds double, double* %151, i64 %153
%155 = load double, double* %154
store double %155, double* %16
%156 = load double*, double** %6
%157 = load i32, i32* %13
%158 = add nsw i32 %157, 1
%159 = sext i32 %158 to i64
%160 = getelementptr inbounds double, double* %156, i64 %159
%161 = load double, double* %160
store double %161, double* %17
%162 = load double, double* %16
%163 = load double, double* %16
%164 = load double, double* %17
%165 = load double, double* %17
%166 = fmul double %164, %165
%167 = fneg double %166
%168 = call double @llvm.fmuladd.f64(double %162, double %163, double %167)
%169 = load double*, double** %6
%170 = load i32, i32* %13
%171 = sext i32 %170 to i64
%172 = getelementptr inbounds double, double* %169, i64 %171
store double %168, double* %172
%173 = load double, double* %16
%174 = fmul double 2.000000e+00, %173
%175 = load double, double* %17
%176 = fmul double %174, %175
%177 = load double*, double** %6
%178 = load i32, i32* %13
%179 = add nsw i32 %178, 1
%180 = sext i32 %179 to i64
%181 = getelementptr inbounds double, double* %177, i64 %180
store double %176, double* %181
ret void
}

LLVM IR (-O2):
define void @mp_mul_rcsqu_nt_in(i32 %0, double* nocapture %1, i32 %2, double* nocapture %3) {
%5 = ashr i32 %0, 1
%6 = icmp sgt i32 %0, 5
br i1 %6, label %9, label %7
7: ; preds = %4
%8 = sext i32 %5 to i64
br label %72
9: ; preds = %4
%10 = shl i32 %2, 2
%11 = sdiv i32 %10, %0
%12 = zext i32 %0 to i64
%13 = sext i32 %5 to i64
%14 = sext i32 %11 to i64
%15 = sext i32 %2 to i64
br label %16
16: ; preds = %9, %16
%17 = phi i64 [ 0, %9 ], [ %20, %16 ]
%18 = phi i64 [ 2, %9 ], [ %70, %16 ]
%19 = sub nsw i64 %12, %18
%20 = add nsw i64 %17, %14
%21 = sub nsw i64 %15, %20
%22 = getelementptr inbounds double, double* %3, i64 %21
%23 = load double, double* %22
%24 = fsub double 5.000000e-01, %23
%25 = getelementptr inbounds double, double* %3, i64 %20
%26 = load double, double* %25
%27 = getelementptr inbounds double, double* %1, i64 %18
%28 = load double, double* %27
%29 = or i64 %18, 1
%30 = getelementptr inbounds double, double* %1, i64 %29
%31 = load double, double* %30
%32 = getelementptr inbounds double, double* %1, i64 %19
%33 = load double, double* %32
%34 = add nsw i64 %19, 1
%35 = getelementptr inbounds double, double* %1, i64 %34
%36 = load double, double* %35
%37 = fneg double %31
%38 = fmul double %31, %37
%39 = tail call double @llvm.fmuladd.f64(double %28, double %28, double %38)
%40 = fmul double %28, 2.000000e+00
%41 = fmul double %40, %31
%42 = fneg double %36
%43 = fmul double %36, %42
%44 = tail call double @llvm.fmuladd.f64(double %33, double %33, double %43)
%45 = fmul double %33, 2.000000e+00
%46 = fmul double %45, %36
%47 = insertelement <2 x double> poison, double %39, i64 0
%48 = insertelement <2 x double> %47, double %41, i64 1
%49 = insertelement <2 x double> poison, double %44, i64 0
%50 = insertelement <2 x double> %49, double %46, i64 1
%51 = fsub <2 x double> %48, %50
%52 = fadd <2 x double> %48, %50
%53 = shufflevector <2 x double> %51, <2 x double> %52, <2 x i32> <i32 0, i32 3>
%54 = fneg double %26
%55 = insertelement <2 x double> poison, double %26, i64 0
%56 = shufflevector <2 x double> %55, <2 x double> %51, <2 x i32> <i32 0, i32 2>
%57 = extractelement <2 x double> %52, i64 1
%58 = insertelement <2 x double> poison, double %57, i64 0
%59 = insertelement <2 x double> %58, double %54, i64 1
%60 = fmul <2 x double> %56, %59
%61 = insertelement <2 x double> poison, double %24, i64 0
%62 = shufflevector <2 x double> %61, <2 x double> poison, <2 x i32> zeroinitializer
%63 = call <2 x double> @llvm.fmuladd.v2f64(<2 x double> %62, <2 x double> %53, <2 x double> %60)
%64 = fsub <2 x double> %48, %63
%65 = bitcast double* %27 to <2 x double>*
store <2 x double> %64, <2 x double>* %65
%66 = extractelement <2 x double> %63, i64 0
%67 = fadd double %44, %66
store double %67, double* %32
%68 = extractelement <2 x double> %63, i64 1
%69 = fsub double %46, %68
store double %69, double* %35
%70 = add nuw nsw i64 %18, 2
%71 = icmp slt i64 %70, %13
br i1 %71, label %16, label %72
72: ; preds = %16, %7
%73 = phi i64 [ %8, %7 ], [ %13, %16 ]
%74 = getelementptr inbounds double, double* %1, i64 %73
%75 = load double, double* %74
%76 = add nsw i32 %5, 1
%77 = sext i32 %76 to i64
%78 = getelementptr inbounds double, double* %1, i64 %77
%79 = load double, double* %78
%80 = fneg double %79
%81 = fmul double %79, %80
%82 = tail call double @llvm.fmuladd.f64(double %75, double %75, double %81)
store double %82, double* %74
%83 = fmul double %75, 2.000000e+00
%84 = fmul double %83, %79
store double %84, double* %78
ret void
}