int char2hex(char in) {
  switch (in) {
  case '0':
    return 0;
  case '1':
    return 1;
  case '2':
    return 2;
  case '3':
    return 3;
  case '4':
    return 4;
  case '5':
    return 5;
  case '6':
    return 6;
  case '7':
    return 7;
  case '8':
    return 8;
  case '9':
    return 9;
  case 'A':
    return 10;
  case 'B':
    return 11;
  case 'C':
    return 12;
  case 'D':
    return 13;
  case 'E':
    return 14;
  case 'F':
    return 15;
  }
}


x86 assembly (clang, -O0):
<char2hex>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x5(%rbp)
movsbl -0x5(%rbp),%eax
add    $0xffffffd0,%eax
mov    %eax,%ecx
mov    %rcx,-0x10(%rbp)
sub    $0x16,%eax
ja     11ef <char2hex+0xef>
mov    -0x10(%rbp),%rax
lea    0xed5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movl   $0x0,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x1,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x2,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x3,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x4,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x5,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x6,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x7,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x8,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0x9,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xa,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xb,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xc,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xd,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xe,-0x4(%rbp)
jmp    11ef <char2hex+0xef>
movl   $0xf,-0x4(%rbp)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<char2hex>:
add    $0xffffffcf,%edi
xor    %eax,%eax
cmp    $0x15,%edi
ja     1117 <char2hex+0x17>
movslq %edi,%rax
lea    0xeec(%rip),%rcx
mov    (%rcx,%rax,4),%eax
ret

LLVM IR (-O0):
define i32 @char2hex(i8 signext %0) {
%2 = alloca i32
%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 66, label %17
i32 67, label %18
i32 68, label %19
i32 69, label %20
i32 70, label %21
]
6: ; preds = %1
store i32 0, i32* %2
br label %22
7: ; preds = %1
store i32 1, i32* %2
br label %22
8: ; preds = %1
store i32 2, i32* %2
br label %22
9: ; preds = %1
store i32 3, i32* %2
br label %22
10: ; preds = %1
store i32 4, i32* %2
br label %22
11: ; preds = %1
store i32 5, i32* %2
br label %22
12: ; preds = %1
store i32 6, i32* %2
br label %22
13: ; preds = %1
store i32 7, i32* %2
br label %22
14: ; preds = %1
store i32 8, i32* %2
br label %22
15: ; preds = %1
store i32 9, i32* %2
br label %22
16: ; preds = %1
store i32 10, i32* %2
br label %22
17: ; preds = %1
store i32 11, i32* %2
br label %22
18: ; preds = %1
store i32 12, i32* %2
br label %22
19: ; preds = %1
store i32 13, i32* %2
br label %22
20: ; preds = %1
store i32 14, i32* %2
br label %22
21: ; preds = %1
store i32 15, i32* %2
br label %22
22: ; preds = %6, %7, %8, %9, %10, %11, %12, %13, %14, %15, %16, %17, %18, %19, %20, %21, %1
%23 = load i32, i32* %2
ret i32 %23
}

LLVM IR (-O2):
@switch.table.char2hex = [22 x i32] [i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15]
define i32 @char2hex(i8 signext %0) {
%2 = sext i8 %0 to i32
%3 = add nsw i32 %2, -49
%4 = icmp ult i32 %3, 22
br i1 %4, label %5, label %9
5: ; preds = %1
%6 = sext i32 %3 to i64
%7 = getelementptr inbounds [22 x i32], [22 x i32]* @switch.table.char2hex, i64 0, i64 %6
%8 = load i32, i32* %7
br label %9
9: ; preds = %5, %1
%10 = phi i32 [ 0, %1 ], [ %8, %5 ]
ret i32 %10
}