char *digit_to_word(int n) {
  switch (n) {
  case 0:
    return "zero";
    break;
  case 1:
    return "one";
    break;
  case 2:
    return "two";
    break;
  case 3:
    return "three";
    break;
  case 4:
    return "four";
    break;
  case 5:
    return "five";
    break;
  case 6:
    return "six";
    break;
  case 7:
    return "seven";
    break;
  case 8:
    return "eight";
    break;
  case 9:
    return "nine";
    break;
  default:
    return "";
    break;
  }
}


x86 assembly (clang, -O0):
<digit_to_word>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0xc(%rbp)
mov    -0xc(%rbp),%eax
mov    %rax,-0x18(%rbp)
sub    $0x9,%rax
ja     11cc <digit_to_word+0xcc>
mov    -0x18(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xef5(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xeea(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xede(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xed2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xec8(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xebd(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xeb2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xea6(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xe9c(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xe92(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11d7 <digit_to_word+0xd7>
lea    0xe67(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<digit_to_word>:
cmp    $0x9,%edi
ja     1117 <digit_to_word+0x17>
movslq %edi,%rax
lea    0xf25(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xef4(%rip),%rax
ret

LLVM IR (-O0):
@.str = [5 x i8] c"zero\00"
@.str.1 = [4 x i8] c"one\00"
@.str.2 = [4 x i8] c"two\00"
@.str.3 = [6 x i8] c"three\00"
@.str.4 = [5 x i8] c"four\00"
@.str.5 = [5 x i8] c"five\00"
@.str.6 = [4 x i8] c"six\00"
@.str.7 = [6 x i8] c"seven\00"
@.str.8 = [6 x i8] c"eight\00"
@.str.9 = [5 x i8] c"nine\00"
@.str.10 = [1 x i8] zeroinitializer
define i8* @digit_to_word(i32 %0) {
%2 = alloca i8*
%3 = alloca i32
store i32 %0, i32* %3
%4 = load i32, i32* %3
switch i32 %4, label %15 [
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
]
5: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8** %2
br label %16
6: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %16
7: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %16
8: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %16
9: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %16
10: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %16
11: ; preds = %1
store i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %16
12: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %16
13: ; preds = %1
store i8* getelementptr inbounds ([6 x i8], [6 x i8]* @.str.8, i64 0, i64 0), i8** %2
br label %16
14: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.9, i64 0, i64 0), i8** %2
br label %16
15: ; preds = %1
store i8* getelementptr inbounds ([1 x i8], [1 x i8]* @.str.10, i64 0, i64 0), i8** %2
br label %16
16: ; preds = %15, %14, %13, %12, %11, %10, %9, %8, %7, %6, %5
%17 = load i8*, i8** %2
ret i8* %17
}

LLVM IR (-O2):
@.str = [5 x i8] c"zero\00"
@.str.1 = [4 x i8] c"one\00"
@.str.2 = [4 x i8] c"two\00"
@.str.3 = [6 x i8] c"three\00"
@.str.4 = [5 x i8] c"four\00"
@.str.5 = [5 x i8] c"five\00"
@.str.6 = [4 x i8] c"six\00"
@.str.7 = [6 x i8] c"seven\00"
@.str.8 = [6 x i8] c"eight\00"
@.str.9 = [5 x i8] c"nine\00"
@.str.10 = [1 x i8] zeroinitializer
@reltable.digit_to_word = [10 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.1 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.2 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.3 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.4 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.5 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([4 x i8]* @.str.6 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.7 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([6 x i8]* @.str.8 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.9 to i64), i64 ptrtoint ([10 x i32]* @reltable.digit_to_word to i64)) to i32)]
define i8* @digit_to_word(i32 %0) {
%2 = icmp ult i32 %0, 10
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 ([10 x i32]* @reltable.digit_to_word to i8*), i64 %5)
br label %7
7: ; preds = %1, %3
%8 = phi i8* [ %6, %3 ], [ getelementptr inbounds ([1 x i8], [1 x i8]* @.str.10, i64 0, i64 0), %1 ]
ret i8* %8
}