long long int presum(int a) {
  switch (a) {
  case 0:
    return 0;
  case 1:
    return 5;
  case 2:
    return -40;
  case 3:
    return 410;
  case 4:
    return -4090;
  case 5:
    return 40910;
  case 6:
    return -409090;
  case 7:
    return 4090910;
  case 8:
    return -40909090;
  case 9:
    return 409090910;
  case 10:
    return 4090909090;
  case 11:
    return 40909090910;
  case 12:
    return -409090909090;
  case 13:
    return 4090909090910;
  case 14:
    return -40909090909090;
  case 15:
    return 409090909090910;
  }
}


x86 assembly (clang, -O0):
<presum>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0xf,%rax
ja     1216 <presum+0x116>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movq   $0x0,-0x8(%rbp)
jmp    1216 <presum+0x116>
movq   $0x5,-0x8(%rbp)
jmp    1216 <presum+0x116>
movq   $0xffffffffffffffd8,-0x8(%rbp)
ff
jmp    1216 <presum+0x116>
movq   $0x19a,-0x8(%rbp)
jmp    1216 <presum+0x116>
movq   $0xfffffffffffff006,-0x8(%rbp)
ff
jmp    1216 <presum+0x116>
movq   $0x9fce,-0x8(%rbp)
jmp    1216 <presum+0x116>
movq   $0xfffffffffff9c1fe,-0x8(%rbp)
ff
jmp    1216 <presum+0x116>
movq   $0x3e6c1e,-0x8(%rbp)
jmp    1216 <presum+0x116>
movq   $0xfffffffffd8fc6de,-0x8(%rbp)
fd
jmp    1216 <presum+0x116>
movq   $0x18623b5e,-0x8(%rbp)
18
jmp    1216 <presum+0x116>
mov    $0xf3d651a2,%eax
mov    %rax,-0x8(%rbp)
jmp    1216 <presum+0x116>
movabs $0x9865f305e,%rax
mov    %rax,-0x8(%rbp)
jmp    1216 <presum+0x116>
movabs $0xffffffa0c0481c5e,%rax
ff ff ff
mov    %rax,-0x8(%rbp)
jmp    1216 <presum+0x116>
movabs $0x3b87d2ee45e,%rax
mov    %rax,-0x8(%rbp)
jmp    1216 <presum+0x116>
movabs $0xffffdacb1c2b145e,%rax
da ff ff
mov    %rax,-0x8(%rbp)
jmp    1216 <presum+0x116>
movabs $0x17410e651345e,%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<presum>:
add    $0xffffffff,%edi
cmp    $0xe,%edi
ja     1117 <presum+0x17>
movslq %edi,%rax
lea    0xeee(%rip),%rcx
mov    (%rcx,%rax,8),%rax
ret
xor    %eax,%eax
ret

LLVM IR (-O0):
define i64 @presum(i32 %0) {
%2 = alloca i64
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %21 [
i32 0, label %5
i32 1, label %6
i32 2, label %7
i32 3, label %8
i32 4, label %9
i32 5, label %10
i32 6, label %11
i32 7, label %12
i32 8, label %13
i32 9, label %14
i32 10, label %15
i32 11, label %16
i32 12, label %17
i32 13, label %18
i32 14, label %19
i32 15, label %20
]
5: ; preds = %1
store i64 0, i64* %2
br label %21
6: ; preds = %1
store i64 5, i64* %2
br label %21
7: ; preds = %1
store i64 -40, i64* %2
br label %21
8: ; preds = %1
store i64 410, i64* %2
br label %21
9: ; preds = %1
store i64 -4090, i64* %2
br label %21
10: ; preds = %1
store i64 40910, i64* %2
br label %21
11: ; preds = %1
store i64 -409090, i64* %2
br label %21
12: ; preds = %1
store i64 4090910, i64* %2
br label %21
13: ; preds = %1
store i64 -40909090, i64* %2
br label %21
14: ; preds = %1
store i64 409090910, i64* %2
br label %21
15: ; preds = %1
store i64 4090909090, i64* %2
br label %21
16: ; preds = %1
store i64 40909090910, i64* %2
br label %21
17: ; preds = %1
store i64 -409090909090, i64* %2
br label %21
18: ; preds = %1
store i64 4090909090910, i64* %2
br label %21
19: ; preds = %1
store i64 -40909090909090, i64* %2
br label %21
20: ; preds = %1
store i64 409090909090910, i64* %2
br label %21
21: ; preds = %5, %6, %7, %8, %9, %10, %11, %12, %13, %14, %15, %16, %17, %18, %19, %20, %1
%22 = load i64, i64* %2
ret i64 %22
}

LLVM IR (-O2):
@switch.table.presum = [15 x i64] [i64 5, i64 -40, i64 410, i64 -4090, i64 40910, i64 -409090, i64 4090910, i64 -40909090, i64 409090910, i64 4090909090, i64 40909090910, i64 -409090909090, i64 4090909090910, i64 -40909090909090, i64 409090909090910]
define i64 @presum(i32 %0) {
%2 = add i32 %0, -1
%3 = icmp ult i32 %2, 15
br i1 %3, label %4, label %8
4: ; preds = %1
%5 = sext i32 %2 to i64
%6 = getelementptr inbounds [15 x i64], [15 x i64]* @switch.table.presum, i64 0, i64 %5
%7 = load i64, i64* %6
br label %8
8: ; preds = %4, %1
%9 = phi i64 [ 0, %1 ], [ %7, %4 ]
ret i64 %9
}