const char *mqtt_strerror(int ret) {
  switch (ret) {
  case 0:
    return "Connection Accepted";
  case 1:
    return "Connection Refused: unacceptable protocol version";
  case 2:
    return "Connection Refused: identifier rejected";
  case 3:
    return "Connection Refused: server unavailable";
  case 4:
    return "Connection Refused: bad user name or password";
  case 5:
    return "Connection Refused: not authorized";
  default:
    return "uknown errror";
  }
}


x86 assembly (clang, -O0):
<mqtt_strerror>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x5,%rax
ja     118c <mqtt_strerror+0x8c>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xee5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xee9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xf0b(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xf23(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xf3a(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xf58(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1197 <mqtt_strerror+0x97>
lea    0xf6b(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<mqtt_strerror>:
cmp    $0x5,%edi
ja     1117 <mqtt_strerror+0x17>
movslq %edi,%rax
lea    0xfe5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xfc8(%rip),%rax
ret

LLVM IR (-O0):
@.str = [20 x i8] c"Connection Accepted\00"
@.str.1 = [50 x i8] c"Connection Refused: unacceptable protocol version\00"
@.str.2 = [40 x i8] c"Connection Refused: identifier rejected\00"
@.str.3 = [39 x i8] c"Connection Refused: server unavailable\00"
@.str.4 = [46 x i8] c"Connection Refused: bad user name or password\00"
@.str.5 = [35 x i8] c"Connection Refused: not authorized\00"
@.str.6 = [14 x i8] c"uknown errror\00"
define i8* @mqtt_strerror(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %11 [
i32 0, label %5
i32 1, label %6
i32 2, label %7
i32 3, label %8
i32 4, label %9
i32 5, label %10
]
5: ; preds = %1
store i8* getelementptr inbounds ([20 x i8], [20 x i8]* @.str, i64 0, i64 0), i8** %2
br label %12
6: ; preds = %1
store i8* getelementptr inbounds ([50 x i8], [50 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %12
7: ; preds = %1
store i8* getelementptr inbounds ([40 x i8], [40 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %12
8: ; preds = %1
store i8* getelementptr inbounds ([39 x i8], [39 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %12
9: ; preds = %1
store i8* getelementptr inbounds ([46 x i8], [46 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %12
10: ; preds = %1
store i8* getelementptr inbounds ([35 x i8], [35 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %12
11: ; preds = %1
store i8* getelementptr inbounds ([14 x i8], [14 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %12
12: ; preds = %11, %10, %9, %8, %7, %6, %5
%13 = load i8*, i8** %2
ret i8* %13
}

LLVM IR (-O2):
@.str = [20 x i8] c"Connection Accepted\00"
@.str.1 = [50 x i8] c"Connection Refused: unacceptable protocol version\00"
@.str.2 = [40 x i8] c"Connection Refused: identifier rejected\00"
@.str.3 = [39 x i8] c"Connection Refused: server unavailable\00"
@.str.4 = [46 x i8] c"Connection Refused: bad user name or password\00"
@.str.5 = [35 x i8] c"Connection Refused: not authorized\00"
@.str.6 = [14 x i8] c"uknown errror\00"
@reltable.mqtt_strerror = [6 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([20 x i8]* @.str to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([50 x i8]* @.str.1 to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([40 x i8]* @.str.2 to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([39 x i8]* @.str.3 to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([46 x i8]* @.str.4 to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([35 x i8]* @.str.5 to i64), i64 ptrtoint ([6 x i32]* @reltable.mqtt_strerror to i64)) to i32)]
define i8* @mqtt_strerror(i32 %0) {
%2 = icmp ult i32 %0, 6
br i1 %2, label %3, label %7
3: ; preds = %1
%4 = sext i32 %0 to i64
%5 = shl i64 %4, 2
%6 = call i8* @llvm.load.relative.i64(i8* bitcast ([6 x i32]* @reltable.mqtt_strerror to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([14 x i8], [14 x i8]* @.str.6, i64 0, i64 0), %1 ]
ret i8* %8
}