unsigned char firetalk_debase64_char(const char c) {
  if ((c >= 'A') && (c <= 'Z'))
    return ((unsigned char)(c - 'A'));
  if ((c >= 'a') && (c <= 'z'))
    return ((unsigned char)(26 + (c - 'a')));
  if ((c >= '0') && (c <= '9'))
    return ((unsigned char)(52 + (c - '0')));
  if (c == '+')
    return ((unsigned char)62);
  if (c == '/')
    return ((unsigned char)63);
  return ((unsigned char)0);
}


x86 assembly (clang, -O0):
<firetalk_debase64_char>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x2(%rbp)
movsbl -0x2(%rbp),%eax
cmp    $0x41,%eax
jl     1133 <firetalk_debase64_char+0x33>
movsbl -0x2(%rbp),%eax
cmp    $0x5a,%eax
jg     1133 <firetalk_debase64_char+0x33>
movsbl -0x2(%rbp),%eax
sub    $0x41,%eax
mov    %al,-0x1(%rbp)
jmp    11bb <firetalk_debase64_char+0xbb>
movsbl -0x2(%rbp),%eax
cmp    $0x61,%eax
jl     115f <firetalk_debase64_char+0x5f>
movsbl -0x2(%rbp),%eax
cmp    $0x7a,%eax
jg     115f <firetalk_debase64_char+0x5f>
movsbl -0x2(%rbp),%eax
sub    $0x61,%eax
add    $0x1a,%eax
mov    %al,-0x1(%rbp)
jmp    11bb <firetalk_debase64_char+0xbb>
movsbl -0x2(%rbp),%eax
cmp    $0x30,%eax
jl     118b <firetalk_debase64_char+0x8b>
movsbl -0x2(%rbp),%eax
cmp    $0x39,%eax
jg     118b <firetalk_debase64_char+0x8b>
movsbl -0x2(%rbp),%eax
sub    $0x30,%eax
add    $0x34,%eax
mov    %al,-0x1(%rbp)
jmp    11bb <firetalk_debase64_char+0xbb>
movsbl -0x2(%rbp),%eax
cmp    $0x2b,%eax
jne    11a1 <firetalk_debase64_char+0xa1>
movb   $0x3e,-0x1(%rbp)
jmp    11bb <firetalk_debase64_char+0xbb>
movsbl -0x2(%rbp),%eax
cmp    $0x2f,%eax
jne    11b7 <firetalk_debase64_char+0xb7>
movb   $0x3f,-0x1(%rbp)
jmp    11bb <firetalk_debase64_char+0xbb>
movb   $0x0,-0x1(%rbp)
movzbl -0x1(%rbp),%eax
pop    %rbp
ret

x86 assembly (clang, -O2):
<firetalk_debase64_char>:
lea    -0x41(%rdi),%eax
cmp    $0x1a,%al
jb     113d <firetalk_debase64_char+0x3d>
lea    -0x61(%rdi),%eax
cmp    $0x19,%al
ja     1115 <firetalk_debase64_char+0x15>
add    $0xb9,%dil
mov    %edi,%eax
ret
lea    -0x30(%rdi),%eax
cmp    $0x9,%al
ja     1123 <firetalk_debase64_char+0x23>
add    $0x4,%dil
mov    %edi,%eax
ret
xor    %eax,%eax
cmp    $0x2f,%dil
mov    $0x3f,%ecx
cmovne %eax,%ecx
cmp    $0x2b,%dil
mov    $0x3e,%eax
cmovne %ecx,%eax
ret

LLVM IR (-O0):
define zeroext i8 @firetalk_debase64_char(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
%6 = icmp sge i32 %5, 65
br i1 %6, label %7, label %16
7: ; preds = %1
%8 = load i8, i8* %3
%9 = sext i8 %8 to i32
%10 = icmp sle i32 %9, 90
br i1 %10, label %11, label %16
11: ; preds = %7
%12 = load i8, i8* %3
%13 = sext i8 %12 to i32
%14 = sub nsw i32 %13, 65
%15 = trunc i32 %14 to i8
store i8 %15, i8* %2
br label %55
16: ; preds = %7, %1
%17 = load i8, i8* %3
%18 = sext i8 %17 to i32
%19 = icmp sge i32 %18, 97
br i1 %19, label %20, label %30
20: ; preds = %16
%21 = load i8, i8* %3
%22 = sext i8 %21 to i32
%23 = icmp sle i32 %22, 122
br i1 %23, label %24, label %30
24: ; preds = %20
%25 = load i8, i8* %3
%26 = sext i8 %25 to i32
%27 = sub nsw i32 %26, 97
%28 = add nsw i32 26, %27
%29 = trunc i32 %28 to i8
store i8 %29, i8* %2
br label %55
30: ; preds = %20, %16
%31 = load i8, i8* %3
%32 = sext i8 %31 to i32
%33 = icmp sge i32 %32, 48
br i1 %33, label %34, label %44
34: ; preds = %30
%35 = load i8, i8* %3
%36 = sext i8 %35 to i32
%37 = icmp sle i32 %36, 57
br i1 %37, label %38, label %44
38: ; preds = %34
%39 = load i8, i8* %3
%40 = sext i8 %39 to i32
%41 = sub nsw i32 %40, 48
%42 = add nsw i32 52, %41
%43 = trunc i32 %42 to i8
store i8 %43, i8* %2
br label %55
44: ; preds = %34, %30
%45 = load i8, i8* %3
%46 = sext i8 %45 to i32
%47 = icmp eq i32 %46, 43
br i1 %47, label %48, label %49
48: ; preds = %44
store i8 62, i8* %2
br label %55
49: ; preds = %44
%50 = load i8, i8* %3
%51 = sext i8 %50 to i32
%52 = icmp eq i32 %51, 47
br i1 %52, label %53, label %54
53: ; preds = %49
store i8 63, i8* %2
br label %55
54: ; preds = %49
store i8 0, i8* %2
br label %55
55: ; preds = %54, %53, %48, %38, %24, %11
%56 = load i8, i8* %2
ret i8 %56
}

LLVM IR (-O2):
define zeroext i8 @firetalk_debase64_char(i8 signext %0) {
%2 = add i8 %0, -65
%3 = icmp ult i8 %2, 26
br i1 %3, label %19, label %4
4: ; preds = %1
%5 = add i8 %0, -97
%6 = icmp ult i8 %5, 26
br i1 %6, label %7, label %9
7: ; preds = %4
%8 = add nsw i8 %0, -71
br label %19
9: ; preds = %4
%10 = add i8 %0, -48
%11 = icmp ult i8 %10, 10
br i1 %11, label %12, label %14
12: ; preds = %9
%13 = add nuw nsw i8 %0, 4
br label %19
14: ; preds = %9
%15 = icmp eq i8 %0, 47
%16 = select i1 %15, i8 63, i8 0
%17 = icmp eq i8 %0, 43
%18 = select i1 %17, i8 62, i8 %16
br label %19
19: ; preds = %1, %14, %12, %7
%20 = phi i8 [ %8, %7 ], [ %13, %12 ], [ %18, %14 ], [ %2, %1 ]
ret i8 %20
}