char *userpart2str(unsigned char userpart) {
  switch (userpart) {
  case 0x00:
    return "NET_MNG";
  case 0x01:
    return "STD_TEST";
  case 0x02:
    return "SPEC_TEST";
  case 0x03:
    return "SCCP";
  case 0x05:
    return "ISUP";
  default:
    return "Unknown";
  }
}


x86 assembly (clang, -O0):
<userpart2str>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x9(%rbp)
movzbl -0x9(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x5,%rax
ja     1180 <userpart2str+0x80>
mov    -0x18(%rbp),%rax
lea    0xed9(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xee1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <userpart2str+0x8b>
lea    0xed9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <userpart2str+0x8b>
lea    0xed2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <userpart2str+0x8b>
lea    0xecc(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <userpart2str+0x8b>
lea    0xec1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    118b <userpart2str+0x8b>
lea    0xeb6(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<userpart2str>:
cmp    $0x5,%dil
ja     1119 <userpart2str+0x19>
movsbq %dil,%rax
lea    0xf1f(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xf05(%rip),%rax
ret

LLVM IR (-O0):
@.str = [8 x i8] c"NET_MNG\00"
@.str.1 = [9 x i8] c"STD_TEST\00"
@.str.2 = [10 x i8] c"SPEC_TEST\00"
@.str.3 = [5 x i8] c"SCCP\00"
@.str.4 = [5 x i8] c"ISUP\00"
@.str.5 = [8 x i8] c"Unknown\00"
define i8* @userpart2str(i8 zeroext %0) {
%2 = alloca i8*
%3 = alloca i8
store i8 %0, i8* %3
%4 = load i8, i8* %3
%5 = zext i8 %4 to i32
switch i32 %5, label %11 [
i32 0, label %6
i32 1, label %7
i32 2, label %8
i32 3, label %9
i32 5, label %10
]
6: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str, i64 0, i64 0), i8** %2
br label %12
7: ; preds = %1
store i8* getelementptr inbounds ([9 x i8], [9 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %12
8: ; preds = %1
store i8* getelementptr inbounds ([10 x i8], [10 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %12
9: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %12
10: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %12
11: ; preds = %1
store i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %12
12: ; preds = %11, %10, %9, %8, %7, %6
%13 = load i8*, i8** %2
ret i8* %13
}

LLVM IR (-O2):
@.str = [8 x i8] c"NET_MNG\00"
@.str.1 = [9 x i8] c"STD_TEST\00"
@.str.2 = [10 x i8] c"SPEC_TEST\00"
@.str.3 = [5 x i8] c"SCCP\00"
@.str.4 = [5 x i8] c"ISUP\00"
@.str.5 = [8 x i8] c"Unknown\00"
@reltable.userpart2str = [6 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([9 x i8]* @.str.1 to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([10 x i8]* @.str.2 to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.3 to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([8 x i8]* @.str.5 to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.4 to i64), i64 ptrtoint ([6 x i32]* @reltable.userpart2str to i64)) to i32)]
define i8* @userpart2str(i8 zeroext %0) {
%2 = icmp ult i8 %0, 6
br i1 %2, label %3, label %7
3: ; preds = %1
%4 = sext i8 %0 to i64
%5 = shl i64 %4, 2
%6 = call i8* @llvm.load.relative.i64(i8* bitcast ([6 x i32]* @reltable.userpart2str to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([8 x i8], [8 x i8]* @.str.5, i64 0, i64 0), %1 ]
ret i8* %8
}