char lettreToChar(char lettre) {
  switch (lettre) {
  case '0':
    return 0;
    break;
  case '1':
    return 1;
    break;
  case '2':
    return 2;
    break;
  case '3':
    return 3;
    break;
  case '4':
    return 4;
    break;
  case '5':
    return 5;
    break;
  case '6':
    return 6;
    break;
  case '7':
    return 7;
    break;
  case '8':
    return 8;
    break;
  case '9':
    return 9;
    break;
  case 'a':
    return 10;
    break;
  case 'b':
    return 11;
    break;
  case 'c':
    return 12;
    break;
  case 'd':
    return 13;
    break;
  case 'e':
    return 14;
    break;
  case 'f':
    return 15;
    break;
  }
}


x86 assembly (clang, -O0):
<lettreToChar>:
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     11bf <lettreToChar+0xbf>
mov    -0x10(%rbp),%rax
lea    0xed5(%rip),%rcx
movslq (%rcx,%rax,4),%rax
add    %rcx,%rax
jmp    *%rax
movb   $0x0,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x1,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x2,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x3,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x4,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x5,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x6,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x7,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x8,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0x9,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xa,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xb,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xc,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xd,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xe,-0x1(%rbp)
jmp    11bf <lettreToChar+0xbf>
movb   $0xf,-0x1(%rbp)
movsbl -0x1(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<lettreToChar>:
xor    %eax,%eax
add    $0xffffffcf,%edi
cmp    $0x35,%edi
ja     1143 <lettreToChar+0x43>
lea    0xeef(%rip),%rcx
movslq (%rcx,%rdi,4),%rdx
add    %rcx,%rdx
jmp    *%rdx
mov    $0x1,%al
ret
mov    $0x2,%al
ret
mov    $0x3,%al
ret
mov    $0x4,%al
ret
mov    $0x5,%al
ret
mov    $0x6,%al
ret
mov    $0x7,%al
ret
mov    $0x8,%al
ret
mov    $0xa,%al
ret
mov    $0xb,%al
ret
mov    $0xc,%al
ret
mov    $0xd,%al
ret
mov    $0xe,%al
ret
mov    $0xf,%al
ret
mov    $0x9,%al
ret

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

LLVM IR (-O2):
define signext i8 @lettreToChar(i8 signext %0) {
%2 = sext i8 %0 to i32
switch i32 %2, label %18 [
i32 102, label %17
i32 49, label %3
i32 50, label %4
i32 51, label %5
i32 52, label %6
i32 53, label %7
i32 54, label %8
i32 55, label %9
i32 56, label %10
i32 57, label %11
i32 97, label %12
i32 98, label %13
i32 99, label %14
i32 100, label %15
i32 101, label %16
]
3: ; preds = %1
br label %18
4: ; preds = %1
br label %18
5: ; preds = %1
br label %18
6: ; preds = %1
br label %18
7: ; preds = %1
br label %18
8: ; preds = %1
br label %18
9: ; preds = %1
br label %18
10: ; preds = %1
br label %18
11: ; preds = %1
br label %18
12: ; preds = %1
br label %18
13: ; preds = %1
br label %18
14: ; preds = %1
br label %18
15: ; preds = %1
br label %18
16: ; preds = %1
br label %18
17: ; preds = %1
br label %18
18: ; preds = %3, %4, %5, %6, %7, %8, %9, %10, %11, %12, %13, %14, %15, %16, %17, %1
%19 = phi i8 [ 15, %17 ], [ 14, %16 ], [ 13, %15 ], [ 12, %14 ], [ 11, %13 ], [ 10, %12 ], [ 9, %11 ], [ 8, %10 ], [ 7, %9 ], [ 6, %8 ], [ 5, %7 ], [ 4, %6 ], [ 3, %5 ], [ 2, %4 ], [ 1, %3 ], [ 0, %1 ]
ret i8 %19
}