char *icmpcode_v4(int code) {
  switch (code) {
  case 0:
    return ("network unreachable");
  case 1:
    return ("host unreachable");
  case 2:
    return ("protocol unreachable");
  case 3:
    return ("port unreachable");
  case 4:
    return ("fragmentation required but DF bit set");
  case 5:
    return ("source route failed");
  case 6:
    return ("destination network unknown");
  case 7:
    return ("destination host unknown");
  case 8:
    return ("source host isolated (obsolete)");
  case 9:
    return ("destination network administratively prohibited");
  case 10:
    return ("destination host administratively prohibited");
  case 11:
    return ("network unreachable for TOS");
  case 12:
    return ("host unreachable for TOS");
  case 13:
    return ("communication administratively prohibited by filtering");
  case 14:
    return ("host recedence violation");
  case 15:
    return ("precedence cutoff in effect");
  default:
    return ("[unknown code]");
  }
}


x86 assembly (clang, -O0):
<icmpcode_v4>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0xf,%rax
ja     122c <icmpcode_v4+0x12c>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xf0d(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf11(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf12(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf17(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf18(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf2e(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf32(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf3e(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf47(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf57(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf77(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xf94(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xfa0(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xfa9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xfd0(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xfd9(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    1237 <icmpcode_v4+0x137>
lea    0xfe5(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<icmpcode_v4>:
cmp    $0xf,%edi
ja     1117 <icmpcode_v4+0x17>
movslq %edi,%rax
lea    0x10d9(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0x10ba(%rip),%rax
ret

LLVM IR (-O0):
@.str = [20 x i8] c"network unreachable\00"
@.str.1 = [17 x i8] c"host unreachable\00"
@.str.2 = [21 x i8] c"protocol unreachable\00"
@.str.3 = [17 x i8] c"port unreachable\00"
@.str.4 = [38 x i8] c"fragmentation required but DF bit set\00"
@.str.5 = [20 x i8] c"source route failed\00"
@.str.6 = [28 x i8] c"destination network unknown\00"
@.str.7 = [25 x i8] c"destination host unknown\00"
@.str.8 = [32 x i8] c"source host isolated (obsolete)\00"
@.str.9 = [48 x i8] c"destination network administratively prohibited\00"
@.str.10 = [45 x i8] c"destination host administratively prohibited\00"
@.str.11 = [28 x i8] c"network unreachable for TOS\00"
@.str.12 = [25 x i8] c"host unreachable for TOS\00"
@.str.13 = [55 x i8] c"communication administratively prohibited by filtering\00"
@.str.14 = [25 x i8] c"host recedence violation\00"
@.str.15 = [28 x i8] c"precedence cutoff in effect\00"
@.str.16 = [15 x i8] c"[unknown code]\00"
define i8* @icmpcode_v4(i32 %0) {
%2 = alloca i8*
%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 i8* getelementptr inbounds ([20 x i8], [20 x i8]* @.str, i64 0, i64 0), i8** %2
br label %22
6: ; preds = %1
store i8* getelementptr inbounds ([17 x i8], [17 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %22
7: ; preds = %1
store i8* getelementptr inbounds ([21 x i8], [21 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %22
8: ; preds = %1
store i8* getelementptr inbounds ([17 x i8], [17 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %22
9: ; preds = %1
store i8* getelementptr inbounds ([38 x i8], [38 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %22
10: ; preds = %1
store i8* getelementptr inbounds ([20 x i8], [20 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %22
11: ; preds = %1
store i8* getelementptr inbounds ([28 x i8], [28 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %22
12: ; preds = %1
store i8* getelementptr inbounds ([25 x i8], [25 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %22
13: ; preds = %1
store i8* getelementptr inbounds ([32 x i8], [32 x i8]* @.str.8, i64 0, i64 0), i8** %2
br label %22
14: ; preds = %1
store i8* getelementptr inbounds ([48 x i8], [48 x i8]* @.str.9, i64 0, i64 0), i8** %2
br label %22
15: ; preds = %1
store i8* getelementptr inbounds ([45 x i8], [45 x i8]* @.str.10, i64 0, i64 0), i8** %2
br label %22
16: ; preds = %1
store i8* getelementptr inbounds ([28 x i8], [28 x i8]* @.str.11, i64 0, i64 0), i8** %2
br label %22
17: ; preds = %1
store i8* getelementptr inbounds ([25 x i8], [25 x i8]* @.str.12, i64 0, i64 0), i8** %2
br label %22
18: ; preds = %1
store i8* getelementptr inbounds ([55 x i8], [55 x i8]* @.str.13, i64 0, i64 0), i8** %2
br label %22
19: ; preds = %1
store i8* getelementptr inbounds ([25 x i8], [25 x i8]* @.str.14, i64 0, i64 0), i8** %2
br label %22
20: ; preds = %1
store i8* getelementptr inbounds ([28 x i8], [28 x i8]* @.str.15, i64 0, i64 0), i8** %2
br label %22
21: ; preds = %1
store i8* getelementptr inbounds ([15 x i8], [15 x i8]* @.str.16, i64 0, i64 0), i8** %2
br label %22
22: ; preds = %21, %20, %19, %18, %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6, %5
%23 = load i8*, i8** %2
ret i8* %23
}

LLVM IR (-O2):
@.str = [20 x i8] c"network unreachable\00"
@.str.1 = [17 x i8] c"host unreachable\00"
@.str.2 = [21 x i8] c"protocol unreachable\00"
@.str.3 = [17 x i8] c"port unreachable\00"
@.str.4 = [38 x i8] c"fragmentation required but DF bit set\00"
@.str.5 = [20 x i8] c"source route failed\00"
@.str.6 = [28 x i8] c"destination network unknown\00"
@.str.7 = [25 x i8] c"destination host unknown\00"
@.str.8 = [32 x i8] c"source host isolated (obsolete)\00"
@.str.9 = [48 x i8] c"destination network administratively prohibited\00"
@.str.10 = [45 x i8] c"destination host administratively prohibited\00"
@.str.11 = [28 x i8] c"network unreachable for TOS\00"
@.str.12 = [25 x i8] c"host unreachable for TOS\00"
@.str.13 = [55 x i8] c"communication administratively prohibited by filtering\00"
@.str.14 = [25 x i8] c"host recedence violation\00"
@.str.15 = [28 x i8] c"precedence cutoff in effect\00"
@.str.16 = [15 x i8] c"[unknown code]\00"
@reltable.icmpcode_v4 = [16 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([20 x i8]* @.str to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([17 x i8]* @.str.1 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([21 x i8]* @.str.2 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([17 x i8]* @.str.3 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([38 x i8]* @.str.4 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([20 x i8]* @.str.5 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([28 x i8]* @.str.6 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([25 x i8]* @.str.7 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([32 x i8]* @.str.8 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([48 x i8]* @.str.9 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([45 x i8]* @.str.10 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([28 x i8]* @.str.11 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([25 x i8]* @.str.12 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([55 x i8]* @.str.13 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([25 x i8]* @.str.14 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([28 x i8]* @.str.15 to i64), i64 ptrtoint ([16 x i32]* @reltable.icmpcode_v4 to i64)) to i32)]
define i8* @icmpcode_v4(i32 %0) {
%2 = icmp ult i32 %0, 16
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 ([16 x i32]* @reltable.icmpcode_v4 to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([15 x i8], [15 x i8]* @.str.16, i64 0, i64 0), %1 ]
ret i8* %8
}