char *single_digit_dec_to_bin(char dec_dig) {
  switch (dec_dig) {
  case '0':
    return "0000";
    break;
  case '1':
    return "0001";
    break;
  case '2':
    return "0010";
    break;
  case '3':
    return "0011";
    break;
  case '4':
    return "0100";
    break;
  case '5':
    return "0101";
    break;
  case '6':
    return "0110";
    break;
  case '7':
    return "0111";
    break;
  case '8':
    return "1000";
    break;
  case '9':
    return "1001";
    break;
  default:
    return "0000";
    break;
  }
}


x86 assembly (clang, -O0):
<single_digit_dec_to_bin>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x9(%rbp)
movsbl -0x9(%rbp),%eax
add    $0xffffffd0,%eax
mov    %eax,%ecx
mov    %rcx,-0x18(%rbp)
sub    $0x9,%eax
ja     11d4 <single_digit_dec_to_bin+0xd4>
mov    -0x18(%rbp),%rax
lea    0xed5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
lea    0xeed(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xee2(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xed7(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xecc(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xec1(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xeb6(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xeab(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xea0(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xe95(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xe8a(%rip),%rax
mov    %rax,-0x8(%rbp)
jmp    11df <single_digit_dec_to_bin+0xdf>
lea    0xe4d(%rip),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
pop    %rbp
ret

x86 assembly (clang, -O2):
<single_digit_dec_to_bin>:
add    $0xffffffcf,%edi
cmp    $0x8,%edi
ja     111a <single_digit_dec_to_bin+0x1a>
movslq %edi,%rax
lea    0xf22(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
ret
lea    0xedf(%rip),%rax
ret

LLVM IR (-O0):
@.str = [5 x i8] c"0000\00"
@.str.1 = [5 x i8] c"0001\00"
@.str.2 = [5 x i8] c"0010\00"
@.str.3 = [5 x i8] c"0011\00"
@.str.4 = [5 x i8] c"0100\00"
@.str.5 = [5 x i8] c"0101\00"
@.str.6 = [5 x i8] c"0110\00"
@.str.7 = [5 x i8] c"0111\00"
@.str.8 = [5 x i8] c"1000\00"
@.str.9 = [5 x i8] c"1001\00"
define i8* @single_digit_dec_to_bin(i8 signext %0) {
%2 = alloca i8*
%3 = alloca i8
store i8 %0, i8* %3
%4 = load i8, i8* %3
%5 = sext i8 %4 to i32
switch i32 %5, label %16 [
i32 48, label %6
i32 49, label %7
i32 50, label %8
i32 51, label %9
i32 52, label %10
i32 53, label %11
i32 54, label %12
i32 55, label %13
i32 56, label %14
i32 57, label %15
]
6: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8** %2
br label %17
7: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.1, i64 0, i64 0), i8** %2
br label %17
8: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.2, i64 0, i64 0), i8** %2
br label %17
9: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.3, i64 0, i64 0), i8** %2
br label %17
10: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.4, i64 0, i64 0), i8** %2
br label %17
11: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.5, i64 0, i64 0), i8** %2
br label %17
12: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.6, i64 0, i64 0), i8** %2
br label %17
13: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.7, i64 0, i64 0), i8** %2
br label %17
14: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.8, i64 0, i64 0), i8** %2
br label %17
15: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str.9, i64 0, i64 0), i8** %2
br label %17
16: ; preds = %1
store i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i8** %2
br label %17
17: ; preds = %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6
%18 = load i8*, i8** %2
ret i8* %18
}

LLVM IR (-O2):
@.str = [5 x i8] c"0000\00"
@.str.1 = [5 x i8] c"0001\00"
@.str.2 = [5 x i8] c"0010\00"
@.str.3 = [5 x i8] c"0011\00"
@.str.4 = [5 x i8] c"0100\00"
@.str.5 = [5 x i8] c"0101\00"
@.str.6 = [5 x i8] c"0110\00"
@.str.7 = [5 x i8] c"0111\00"
@.str.8 = [5 x i8] c"1000\00"
@.str.9 = [5 x i8] c"1001\00"
@reltable.single_digit_dec_to_bin = [9 x i32] [i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.1 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.2 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.3 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.4 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.5 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.6 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.7 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.8 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([5 x i8]* @.str.9 to i64), i64 ptrtoint ([9 x i32]* @reltable.single_digit_dec_to_bin to i64)) to i32)]
define i8* @single_digit_dec_to_bin(i8 signext %0) {
%2 = sext i8 %0 to i32
%3 = add nsw i32 %2, -49
%4 = icmp ult i32 %3, 9
br i1 %4, label %5, label %9
5: ; preds = %1
%6 = sext i32 %3 to i64
%7 = shl i64 %6, 2
%8 = call i8* @llvm.load.relative.i64(i8* bitcast ([9 x i32]* @reltable.single_digit_dec_to_bin to i8*), i64 %7)
br label %9
9: ; preds = %5, %1
%10 = phi i8* [ getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), %1 ], [ %8, %5 ]
ret i8* %10
}