double pythaga(double a, double b) {
  double absa, absb, tmp;
  absa = fabs(a);
  absb = fabs(b);
  if (absa > absb) {
    tmp = absb / absa;
    return absa * sqrt(1.0 + ((tmp) * (tmp)));
  } else {
    tmp = absa / absb;
    return (absb == 0.0 ? 0.0 : absb * sqrt(1.0 + ((tmp) * (tmp))));
  }
}


x86 assembly (clang, -O0):
<pythaga>:
push   %rbp
mov    %rsp,%rbp
sub    $0x50,%rsp
movsd  %xmm0,-0x10(%rbp)
movsd  %xmm1,-0x18(%rbp)
movsd  -0x10(%rbp),%xmm0
movaps 0xed2(%rip),%xmm1
pand   %xmm1,%xmm0
movsd  %xmm0,-0x20(%rbp)
movsd  -0x18(%rbp),%xmm0
movaps 0xebd(%rip),%xmm1
pand   %xmm1,%xmm0
movsd  %xmm0,-0x28(%rbp)
movsd  -0x20(%rbp),%xmm0
ucomisd -0x28(%rbp),%xmm0
jbe    11aa <pythaga+0x9a>
movsd  -0x28(%rbp),%xmm0
divsd  -0x20(%rbp),%xmm0
movsd  %xmm0,-0x30(%rbp)
movsd  -0x20(%rbp),%xmm0
movsd  %xmm0,-0x38(%rbp)
movsd  -0x30(%rbp),%xmm0
movsd  -0x30(%rbp),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xe85(%rip),%xmm1
addsd  %xmm1,%xmm0
call   1030 <sqrt@plt>
movaps %xmm0,%xmm1
movsd  -0x38(%rbp),%xmm0
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x8(%rbp)
jmp    1222 <pythaga+0x112>
movsd  -0x20(%rbp),%xmm0
divsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x30(%rbp)
movsd  -0x28(%rbp),%xmm0
xorps  %xmm1,%xmm1
ucomisd %xmm1,%xmm0
jne    11de <pythaga+0xce>
jp     11de <pythaga+0xce>
xorps  %xmm0,%xmm0
movsd  %xmm0,-0x40(%rbp)
jmp    1218 <pythaga+0x108>
movsd  -0x28(%rbp),%xmm0
movsd  %xmm0,-0x48(%rbp)
movsd  -0x30(%rbp),%xmm0
movsd  -0x30(%rbp),%xmm1
mulsd  %xmm1,%xmm0
movsd  0xe12(%rip),%xmm1
addsd  %xmm1,%xmm0
call   1030 <sqrt@plt>
movaps %xmm0,%xmm1
movsd  -0x48(%rbp),%xmm0
mulsd  %xmm1,%xmm0
movsd  %xmm0,-0x40(%rbp)
movsd  -0x40(%rbp),%xmm0
movsd  %xmm0,-0x8(%rbp)
movsd  -0x8(%rbp),%xmm0
add    $0x50,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<pythaga>:
push   %rax
movapd %xmm0,%xmm2
movapd 0xee3(%rip),%xmm0
andpd  %xmm0,%xmm2
andpd  %xmm1,%xmm0
ucomisd %xmm0,%xmm2
jbe    1141 <pythaga+0x31>
divsd  %xmm2,%xmm0
mulsd  %xmm0,%xmm0
addsd  0xed5(%rip),%xmm0
movapd %xmm2,%xmm3
jmp    1165 <pythaga+0x55>
xorpd  %xmm3,%xmm3
ucomisd %xmm3,%xmm1
jne    114d <pythaga+0x3d>
jnp    1188 <pythaga+0x78>
movapd %xmm0,%xmm3
divsd  %xmm0,%xmm2
mulsd  %xmm2,%xmm2
addsd  0xeaf(%rip),%xmm2
movapd %xmm2,%xmm0
xorpd  %xmm1,%xmm1
ucomisd %xmm1,%xmm0
jb     1175 <pythaga+0x65>
sqrtsd %xmm0,%xmm0
jmp    1184 <pythaga+0x74>
movsd  %xmm3,(%rsp)
call   1030 <sqrt@plt>
movsd  (%rsp),%xmm3
mulsd  %xmm0,%xmm3
movapd %xmm3,%xmm0
pop    %rax
ret

LLVM IR (-O0):
define double @pythaga(double %0, double %1) {
%3 = alloca double
%4 = alloca double
%5 = alloca double
%6 = alloca double
%7 = alloca double
%8 = alloca double
store double %0, double* %4
store double %1, double* %5
%9 = load double, double* %4
%10 = call double @llvm.fabs.f64(double %9)
store double %10, double* %6
%11 = load double, double* %5
%12 = call double @llvm.fabs.f64(double %11)
store double %12, double* %7
%13 = load double, double* %6
%14 = load double, double* %7
%15 = fcmp ogt double %13, %14
br i1 %15, label %16, label %26
16: ; preds = %2
%17 = load double, double* %7
%18 = load double, double* %6
%19 = fdiv double %17, %18
store double %19, double* %8
%20 = load double, double* %6
%21 = load double, double* %8
%22 = load double, double* %8
%23 = call double @llvm.fmuladd.f64(double %21, double %22, double 1.000000e+00)
%24 = call double @sqrt(double %23)
%25 = fmul double %20, %24
store double %25, double* %3
br label %42
26: ; preds = %2
%27 = load double, double* %6
%28 = load double, double* %7
%29 = fdiv double %27, %28
store double %29, double* %8
%30 = load double, double* %7
%31 = fcmp oeq double %30, 0.000000e+00
br i1 %31, label %32, label %33
32: ; preds = %26
br label %40
33: ; preds = %26
%34 = load double, double* %7
%35 = load double, double* %8
%36 = load double, double* %8
%37 = call double @llvm.fmuladd.f64(double %35, double %36, double 1.000000e+00)
%38 = call double @sqrt(double %37)
%39 = fmul double %34, %38
br label %40
40: ; preds = %33, %32
%41 = phi double [ 0.000000e+00, %32 ], [ %39, %33 ]
store double %41, double* %3
br label %42
42: ; preds = %40, %16
%43 = load double, double* %3
ret double %43
}

LLVM IR (-O2):
define double @pythaga(double %0, double %1) {
%3 = tail call double @llvm.fabs.f64(double %0)
%4 = tail call double @llvm.fabs.f64(double %1)
%5 = fcmp ogt double %3, %4
br i1 %5, label %6, label %9
6: ; preds = %2
%7 = fdiv double %4, %3
%8 = tail call double @llvm.fmuladd.f64(double %7, double %7, double 1.000000e+00)
br label %14
9: ; preds = %2
%10 = fcmp oeq double %1, 0.000000e+00
br i1 %10, label %19, label %11
11: ; preds = %9
%12 = fdiv double %3, %4
%13 = tail call double @llvm.fmuladd.f64(double %12, double %12, double 1.000000e+00)
br label %14
14: ; preds = %6, %11
%15 = phi double [ %13, %11 ], [ %8, %6 ]
%16 = phi double [ %4, %11 ], [ %3, %6 ]
%17 = tail call double @sqrt(double %15)
%18 = fmul double %16, %17
br label %19
19: ; preds = %14, %9
%20 = phi double [ 0.000000e+00, %9 ], [ %18, %14 ]
ret double %20
}