unsigned char hex2ui(char hex) {
  switch (hex) {
  case '0': {
    return (0x0);
  }
  case '1': {
    return (0x1);
  }
  case '2': {
    return (0x2);
  }
  case '3': {
    return (0x3);
  }
  case '4': {
    return (0x4);
  }
  case '5': {
    return (0x5);
  }
  case '6': {
    return (0x6);
  }
  case '7': {
    return (0x7);
  }
  case '8': {
    return (0x8);
  }
  case '9': {
    return (0x9);
  }
  case 'A':
  case 'a': {
    return (0xa);
  }
  case 'B':
  case 'b': {
    return (0xb);
  }
  case 'C':
  case 'c': {
    return (0xc);
  }
  case 'D':
  case 'd': {
    return (0xd);
  }
  case 'E':
  case 'e': {
    return (0xe);
  }
  case 'F':
  case 'f': {
    return (0xf);
  }
  }
  return (0xff);
}


x86 assembly (clang, -O0):
<hex2ui>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x2(%rbp)
movsbl -0x2(%rbp),%eax
add    $0xffffffd0,%eax
mov    %eax,%ecx
mov    %rcx,-0x10(%rbp)
sub    $0x36,%eax
ja     11c4 <hex2ui+0xc4>
mov    -0x10(%rbp),%rax
lea    0xed5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movb   $0x0,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x1,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x2,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x3,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x4,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x5,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x6,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x7,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x8,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0x9,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xa,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xb,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xc,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xd,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xe,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xf,-0x1(%rbp)
jmp    11c8 <hex2ui+0xc8>
movb   $0xff,-0x1(%rbp)
movzbl -0x1(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<hex2ui>:
movslq %edi,%rcx
add    $0xffffffffffffffd0,%rcx
mov    $0xff,%al
cmp    $0x36,%ecx
ja     1118 <hex2ui+0x18>
lea    0xeeb(%rip),%rax
mov    (%rcx,%rax,1),%al
ret

LLVM IR (-O0):
define zeroext i8 @hex2ui(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 %22 [
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
i32 65, label %16
i32 97, label %16
i32 66, label %17
i32 98, label %17
i32 67, label %18
i32 99, label %18
i32 68, label %19
i32 100, label %19
i32 69, label %20
i32 101, label %20
i32 70, label %21
i32 102, label %21
]
6: ; preds = %1
store i8 0, i8* %2
br label %23
7: ; preds = %1
store i8 1, i8* %2
br label %23
8: ; preds = %1
store i8 2, i8* %2
br label %23
9: ; preds = %1
store i8 3, i8* %2
br label %23
10: ; preds = %1
store i8 4, i8* %2
br label %23
11: ; preds = %1
store i8 5, i8* %2
br label %23
12: ; preds = %1
store i8 6, i8* %2
br label %23
13: ; preds = %1
store i8 7, i8* %2
br label %23
14: ; preds = %1
store i8 8, i8* %2
br label %23
15: ; preds = %1
store i8 9, i8* %2
br label %23
16: ; preds = %1, %1
store i8 10, i8* %2
br label %23
17: ; preds = %1, %1
store i8 11, i8* %2
br label %23
18: ; preds = %1, %1
store i8 12, i8* %2
br label %23
19: ; preds = %1, %1
store i8 13, i8* %2
br label %23
20: ; preds = %1, %1
store i8 14, i8* %2
br label %23
21: ; preds = %1, %1
store i8 15, i8* %2
br label %23
22: ; preds = %1
store i8 -1, i8* %2
br label %23
23: ; preds = %22, %21, %20, %19, %18, %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6
%24 = load i8, i8* %2
ret i8 %24
}

LLVM IR (-O2):
@switch.table.hex2ui = [55 x i8] c"\00\01\02\03\04\05\06\07\08\09\FF\FF\FF\FF\FF\FF\FF\0A\0B\0C\0D\0E\0F\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\0A\0B\0C\0D\0E\0F"
define zeroext i8 @hex2ui(i8 signext %0) {
%2 = sext i8 %0 to i32
%3 = add nsw i32 %2, -48
%4 = icmp ult i32 %3, 55
br i1 %4, label %5, label %9
5: ; preds = %1
%6 = sext i32 %3 to i64
%7 = getelementptr inbounds [55 x i8], [55 x i8]* @switch.table.hex2ui, i64 0, i64 %6
%8 = load i8, i8* %7
br label %9
9: ; preds = %1, %5
%10 = phi i8 [ %8, %5 ], [ -1, %1 ]
ret i8 %10
}