int hexx(char c) {
  int i = -1;
  switch (c) {
  case '0':
    i = 0;
    break;
  case '1':
    i = 1;
    break;
  case '2':
    i = 2;
    break;
  case '3':
    i = 3;
    break;
  case '4':
    i = 4;
    break;
  case '5':
    i = 5;
    break;
  case '6':
    i = 6;
    break;
  case '7':
    i = 7;
    break;
  case '8':
    i = 8;
    break;
  case '9':
    i = 9;
    break;
  case 'a':
    i = 10;
    break;
  case 'b':
    i = 11;
    break;
  case 'c':
    i = 12;
    break;
  case 'd':
    i = 13;
    break;
  case 'e':
    i = 14;
    break;
  case 'f':
    i = 15;
    break;
  case 'A':
    i = 10;
    break;
  case 'B':
    i = 11;
    break;
  case 'C':
    i = 12;
    break;
  case 'D':
    i = 13;
    break;
  case 'E':
    i = 14;
    break;
  case 'F':
    i = 15;
    break;
  }
  return i;
}


x86 assembly (clang, -O0):
<hexx>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x1(%rbp)
movl   $0xffffffff,-0x8(%rbp)
movsbl -0x1(%rbp),%eax
add    $0xffffffd0,%eax
mov    %eax,%ecx
mov    %rcx,-0x10(%rbp)
sub    $0x36,%eax
ja     123e <hexx+0x13e>
mov    -0x10(%rbp),%rax
lea    0xece(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movl   $0x0,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x1,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x2,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x3,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x4,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x5,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x6,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x7,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x8,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0x9,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xa,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xb,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xc,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xd,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xe,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xf,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xa,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xb,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xc,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xd,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xe,-0x8(%rbp)
jmp    123e <hexx+0x13e>
movl   $0xf,-0x8(%rbp)
mov    -0x8(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<hexx>:
add    $0xffffffd0,%edi
mov    $0xffffffff,%eax
cmp    $0x36,%edi
ja     111a <hexx+0x1a>
movslq %edi,%rax
lea    0xee9(%rip),%rcx
mov    (%rcx,%rax,4),%eax
ret

LLVM IR (-O0):
define i32 @hexx(i8 signext %0) {
%2 = alloca i8
%3 = alloca i32
store i8 %0, i8* %2
store i32 -1, i32* %3
%4 = load i8, i8* %2
%5 = sext i8 %4 to i32
switch i32 %5, label %28 [
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 97, label %16
i32 98, label %17
i32 99, label %18
i32 100, label %19
i32 101, label %20
i32 102, label %21
i32 65, label %22
i32 66, label %23
i32 67, label %24
i32 68, label %25
i32 69, label %26
i32 70, label %27
]
6: ; preds = %1
store i32 0, i32* %3
br label %28
7: ; preds = %1
store i32 1, i32* %3
br label %28
8: ; preds = %1
store i32 2, i32* %3
br label %28
9: ; preds = %1
store i32 3, i32* %3
br label %28
10: ; preds = %1
store i32 4, i32* %3
br label %28
11: ; preds = %1
store i32 5, i32* %3
br label %28
12: ; preds = %1
store i32 6, i32* %3
br label %28
13: ; preds = %1
store i32 7, i32* %3
br label %28
14: ; preds = %1
store i32 8, i32* %3
br label %28
15: ; preds = %1
store i32 9, i32* %3
br label %28
16: ; preds = %1
store i32 10, i32* %3
br label %28
17: ; preds = %1
store i32 11, i32* %3
br label %28
18: ; preds = %1
store i32 12, i32* %3
br label %28
19: ; preds = %1
store i32 13, i32* %3
br label %28
20: ; preds = %1
store i32 14, i32* %3
br label %28
21: ; preds = %1
store i32 15, i32* %3
br label %28
22: ; preds = %1
store i32 10, i32* %3
br label %28
23: ; preds = %1
store i32 11, i32* %3
br label %28
24: ; preds = %1
store i32 12, i32* %3
br label %28
25: ; preds = %1
store i32 13, i32* %3
br label %28
26: ; preds = %1
store i32 14, i32* %3
br label %28
27: ; preds = %1
store i32 15, i32* %3
br label %28
28: ; preds = %1, %27, %26, %25, %24, %23, %22, %21, %20, %19, %18, %17, %16, %15, %14, %13, %12, %11, %10, %9, %8, %7, %6
%29 = load i32, i32* %3
ret i32 %29
}

LLVM IR (-O2):
@switch.table.hexx = [55 x i32] [i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 -1, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15]
define i32 @hexx(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 i32], [55 x i32]* @switch.table.hexx, i64 0, i64 %6
%8 = load i32, i32* %7
br label %9
9: ; preds = %5, %1
%10 = phi i32 [ -1, %1 ], [ %8, %5 ]
ret i32 %10
}