char nibbleToHexChar(int nibble) {
  char result = '?';
  switch (nibble) {
  case 0:
    result = '0';
    break;
  case 1:
    result = '1';
    break;
  case 2:
    result = '2';
    break;
  case 3:
    result = '3';
    break;
  case 4:
    result = '4';
    break;
  case 5:
    result = '5';
    break;
  case 6:
    result = '6';
    break;
  case 7:
    result = '7';
    break;
  case 8:
    result = '8';
    break;
  case 9:
    result = '9';
    break;
  case 10:
    result = 'A';
    break;
  case 11:
    result = 'B';
    break;
  case 12:
    result = 'C';
    break;
  case 13:
    result = 'D';
    break;
  case 14:
    result = 'E';
    break;
  case 15:
    result = 'F';
    break;
  default:
    result = '?';
    break;
  }
  return (result);
}


x86 assembly (clang, -O0):
<nibbleToHexChar>:
push   %rbp
mov    %rsp,%rbp
mov    %edi,-0x4(%rbp)
movb   $0x3f,-0x5(%rbp)
mov    -0x4(%rbp),%eax
mov    %rax,-0x10(%rbp)
sub    $0xf,%rax
ja     11c0 <nibbleToHexChar+0xc0>
mov    -0x10(%rbp),%rax
lea    0xed9(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movb   $0x30,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x31,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x32,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x33,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x34,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x35,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x36,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x37,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x38,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x39,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x41,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x42,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x43,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x44,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x45,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x46,-0x5(%rbp)
jmp    11c4 <nibbleToHexChar+0xc4>
movb   $0x3f,-0x5(%rbp)
movsbl -0x5(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<nibbleToHexChar>:
mov    $0x3f,%al
cmp    $0xf,%edi
ja     1114 <nibbleToHexChar+0x14>
movslq %edi,%rax
lea    0xeef(%rip),%rcx
mov    (%rax,%rcx,1),%al
ret

LLVM IR (-O0):
define signext i8 @nibbleToHexChar(i32 %0) {
%2 = alloca i32
%3 = alloca i8
store i32 %0, i32* %2
store i8 63, i8* %3
%4 = load i32, i32* %2
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* %3
br label %22
6: ; preds = %1
store i8 49, i8* %3
br label %22
7: ; preds = %1
store i8 50, i8* %3
br label %22
8: ; preds = %1
store i8 51, i8* %3
br label %22
9: ; preds = %1
store i8 52, i8* %3
br label %22
10: ; preds = %1
store i8 53, i8* %3
br label %22
11: ; preds = %1
store i8 54, i8* %3
br label %22
12: ; preds = %1
store i8 55, i8* %3
br label %22
13: ; preds = %1
store i8 56, i8* %3
br label %22
14: ; preds = %1
store i8 57, i8* %3
br label %22
15: ; preds = %1
store i8 65, i8* %3
br label %22
16: ; preds = %1
store i8 66, i8* %3
br label %22
17: ; preds = %1
store i8 67, i8* %3
br label %22
18: ; preds = %1
store i8 68, i8* %3
br label %22
19: ; preds = %1
store i8 69, i8* %3
br label %22
20: ; preds = %1
store i8 70, i8* %3
br label %22
21: ; preds = %1
store i8 63, i8* %3
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* %3
ret i8 %23
}

LLVM IR (-O2):
@switch.table.nibbleToHexChar = [16 x i8] c"0123456789ABCDEF"
define signext i8 @nibbleToHexChar(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.nibbleToHexChar, i64 0, i64 %4
%6 = load i8, i8* %5
br label %7
7: ; preds = %1, %3
%8 = phi i8 [ %6, %3 ], [ 63, %1 ]
ret i8 %8
}