char transform_h(int letter) {
  switch (letter) {
  case 0:
    return '0';
    break;
  case 1:
    return '1';
    break;
  case 2:
    return '2';
    break;
  case 3:
    return '3';
    break;
  case 4:
    return '4';
    break;
  case 5:
    return '5';
    break;
  case 6:
    return '6';
    break;
  case 7:
    return '7';
    break;
  case 8:
    return '8';
    break;
  case 9:
    return '9';
    break;
  case 10:
    return 'a';
    break;
  case 11:
    return 'b';
    break;
  case 12:
    return 'c';
    break;
  case 13:
    return 'd';
    break;
  case 14:
    return 'e';
    break;
  case 15:
    return 'f';
    break;
  default:
    return 0;
    break;
  }
}


x86 assembly (clang, -O0):
<transform_h>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0x8(%rbp)
mov    -0x8(%rbp),%eax
mov    %rax,-0x10(%rbp)
sub    $0xf,%rax
ja     11bc <transform_h+0xbc>
mov    -0x10(%rbp),%rax
lea    0xedd(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movb   $0x30,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x31,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x32,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x33,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x34,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x35,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x36,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x37,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x38,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x39,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x61,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x62,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x63,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x64,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x65,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x66,-0x1(%rbp)
jmp    11c0 <transform_h+0xc0>
movb   $0x0,-0x1(%rbp)
movsbl -0x1(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<transform_h>:
cmp    $0xf,%edi
ja     1113 <transform_h+0x13>
movslq %edi,%rax
lea    0xef1(%rip),%rcx
mov    (%rax,%rcx,1),%al
ret
xor    %eax,%eax
ret

LLVM IR (-O0):
define signext i8 @transform_h(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 48, i8* %2
br label %22
6: ; preds = %1
store i8 49, i8* %2
br label %22
7: ; preds = %1
store i8 50, i8* %2
br label %22
8: ; preds = %1
store i8 51, i8* %2
br label %22
9: ; preds = %1
store i8 52, i8* %2
br label %22
10: ; preds = %1
store i8 53, i8* %2
br label %22
11: ; preds = %1
store i8 54, i8* %2
br label %22
12: ; preds = %1
store i8 55, i8* %2
br label %22
13: ; preds = %1
store i8 56, i8* %2
br label %22
14: ; preds = %1
store i8 57, i8* %2
br label %22
15: ; preds = %1
store i8 97, i8* %2
br label %22
16: ; preds = %1
store i8 98, i8* %2
br label %22
17: ; preds = %1
store i8 99, i8* %2
br label %22
18: ; preds = %1
store i8 100, i8* %2
br label %22
19: ; preds = %1
store i8 101, i8* %2
br label %22
20: ; preds = %1
store i8 102, i8* %2
br label %22
21: ; preds = %1
store i8 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):
@switch.table.transform_h = [16 x i8] c"0123456789abcdef"
define signext i8 @transform_h(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 = getelementptr inbounds [16 x i8], [16 x i8]* @switch.table.transform_h, i64 0, i64 %4
%6 = load i8, i8* %5
br label %7
7: ; preds = %1, %3
%8 = phi i8 [ %6, %3 ], [ 0, %1 ]
ret i8 %8
}