int _ds_hex2dec(unsigned char hex) {
  switch (hex) {
  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':
  case 'A':
    return 10;
  case 'b':
  case 'B':
    return 11;
  case 'c':
  case 'C':
    return 12;
  case 'd':
  case 'D':
    return 13;
  case 'e':
  case 'E':
    return 14;
  case 'f':
  case 'F':
    return 15;
  default:
    return -1;
  }
}


x86 assembly (clang, -O0):
<_ds_hex2dec>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x5(%rbp)
movzbl -0x5(%rbp),%eax
add    $0xffffffd0,%eax
mov    %eax,%ecx
mov    %rcx,-0x10(%rbp)
sub    $0x36,%eax
ja     11f4 <_ds_hex2dec+0xf4>
mov    -0x10(%rbp),%rax
lea    0xed5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movl   $0x0,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x1,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x2,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x3,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x4,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x5,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x6,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x7,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x8,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0x9,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xa,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xb,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xc,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xd,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xe,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xf,-0x4(%rbp)
jmp    11fb <_ds_hex2dec+0xfb>
movl   $0xffffffff,-0x4(%rbp)
mov    -0x4(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<_ds_hex2dec>:
add    $0xd0,%dil
mov    $0xffffffff,%eax
cmp    $0x36,%dil
ja     111d <_ds_hex2dec+0x1d>
movsbq %dil,%rax
lea    0xee6(%rip),%rcx
mov    (%rcx,%rax,4),%eax
ret

LLVM IR (-O0):
define i32 @_ds_hex2dec(i8 zeroext %0) {
%2 = alloca i32
%3 = alloca i8
store i8 %0, i8* %3
%4 = load i8, i8* %3
%5 = zext 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 97, label %16
i32 65, label %16
i32 98, label %17
i32 66, label %17
i32 99, label %18
i32 67, label %18
i32 100, label %19
i32 68, label %19
i32 101, label %20
i32 69, label %20
i32 102, label %21
i32 70, label %21
]
6: ; preds = %1
store i32 0, i32* %2
br label %23
7: ; preds = %1
store i32 1, i32* %2
br label %23
8: ; preds = %1
store i32 2, i32* %2
br label %23
9: ; preds = %1
store i32 3, i32* %2
br label %23
10: ; preds = %1
store i32 4, i32* %2
br label %23
11: ; preds = %1
store i32 5, i32* %2
br label %23
12: ; preds = %1
store i32 6, i32* %2
br label %23
13: ; preds = %1
store i32 7, i32* %2
br label %23
14: ; preds = %1
store i32 8, i32* %2
br label %23
15: ; preds = %1
store i32 9, i32* %2
br label %23
16: ; preds = %1, %1
store i32 10, i32* %2
br label %23
17: ; preds = %1, %1
store i32 11, i32* %2
br label %23
18: ; preds = %1, %1
store i32 12, i32* %2
br label %23
19: ; preds = %1, %1
store i32 13, i32* %2
br label %23
20: ; preds = %1, %1
store i32 14, i32* %2
br label %23
21: ; preds = %1, %1
store i32 15, i32* %2
br label %23
22: ; preds = %1
store i32 -1, i32* %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 i32, i32* %2
ret i32 %24
}

LLVM IR (-O2):
@switch.table._ds_hex2dec = [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 @_ds_hex2dec(i8 zeroext %0) {
%2 = add i8 %0, -48
%3 = icmp ult i8 %2, 55
br i1 %3, label %4, label %8
4: ; preds = %1
%5 = sext i8 %2 to i64
%6 = getelementptr inbounds [55 x i32], [55 x i32]* @switch.table._ds_hex2dec, i64 0, i64 %5
%7 = load i32, i32* %6
br label %8
8: ; preds = %1, %4
%9 = phi i32 [ %7, %4 ], [ -1, %1 ]
ret i32 %9
}