void decomp(char b, char *bit) {
  int i;
  unsigned char bits = b;
  for (i = 0; i < 8; i++) {
    bit[i] = '0';
    if ((bits & 1 << 7 - i) > 0) {
      bit[i] = '1';
    }
  }
}


x86 assembly (clang, -O0):
<decomp>:
push   %rbp
mov    %rsp,%rbp
mov    %dil,%al
mov    %al,-0x1(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x1(%rbp),%al
mov    %al,-0x15(%rbp)
movl   $0x0,-0x14(%rbp)
cmpl   $0x8,-0x14(%rbp)
jge    1170 <decomp+0x70>
mov    -0x10(%rbp),%rax
movslq -0x14(%rbp),%rcx
movb   $0x30,(%rax,%rcx,1)
movzbl -0x15(%rbp),%eax
mov    $0x7,%ecx
sub    -0x14(%rbp),%ecx
mov    $0x1,%edx
shl    %cl,%edx
mov    %edx,%ecx
and    %ecx,%eax
cmp    $0x0,%eax
jle    115d <decomp+0x5d>
mov    -0x10(%rbp),%rax
movslq -0x14(%rbp),%rcx
movb   $0x31,(%rax,%rcx,1)
jmp    1162 <decomp+0x62>
mov    -0x14(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x14(%rbp)
jmp    111b <decomp+0x1b>
pop    %rbp
ret

x86 assembly (clang, -O2):
<decomp>:
movd   %edi,%xmm0
pshufd $0x0,%xmm0,%xmm0
movdqa 0xeef(%rip),%xmm1
pand   %xmm0,%xmm1
pand   0xef3(%rip),%xmm0
pxor   %xmm2,%xmm2
pcmpeqd %xmm2,%xmm0
pcmpeqd %xmm2,%xmm1
packssdw %xmm0,%xmm1
packsswb %xmm1,%xmm1
pmovmskb %xmm1,%edi
mov    %edi,%r11d
and    $0x2,%r11b
shr    %r11b
mov    %edi,%r8d
and    $0x4,%r8b
shr    $0x2,%r8b
mov    %edi,%r9d
and    $0x8,%r9b
shr    $0x3,%r9b
mov    %edi,%r10d
and    $0x10,%r10b
shr    $0x4,%r10b
mov    %edi,%ecx
and    $0x20,%cl
shr    $0x5,%cl
mov    %edi,%edx
and    $0x40,%dl
shr    $0x6,%dl
mov    %edi,%eax
sar    $0x7,%al
add    $0x31,%al
mov    %al,(%rsi)
xor    $0x31,%dl
mov    %dl,0x1(%rsi)
xor    $0x31,%cl
mov    %cl,0x2(%rsi)
xor    $0x31,%r10b
mov    %r10b,0x3(%rsi)
xor    $0x31,%r9b
mov    %r9b,0x4(%rsi)
xor    $0x31,%r8b
mov    %r8b,0x5(%rsi)
xor    $0x31,%r11b
mov    %r11b,0x6(%rsi)
and    $0x1,%dil
xor    $0x31,%dil
mov    %dil,0x7(%rsi)
ret

LLVM IR (-O0):
define void @decomp(i8 signext %0, i8* %1) {
%3 = alloca i8
%4 = alloca i8*
%5 = alloca i32
%6 = alloca i8
store i8 %0, i8* %3
store i8* %1, i8** %4
%7 = load i8, i8* %3
store i8 %7, i8* %6
store i32 0, i32* %5
br label %8
8: ; preds = %29, %2
%9 = load i32, i32* %5
%10 = icmp slt i32 %9, 8
br i1 %10, label %11, label %32
11: ; preds = %8
%12 = load i8*, i8** %4
%13 = load i32, i32* %5
%14 = sext i32 %13 to i64
%15 = getelementptr inbounds i8, i8* %12, i64 %14
store i8 48, i8* %15
%16 = load i8, i8* %6
%17 = zext i8 %16 to i32
%18 = load i32, i32* %5
%19 = sub nsw i32 7, %18
%20 = shl i32 1, %19
%21 = and i32 %17, %20
%22 = icmp sgt i32 %21, 0
br i1 %22, label %23, label %28
23: ; preds = %11
%24 = load i8*, i8** %4
%25 = load i32, i32* %5
%26 = sext i32 %25 to i64
%27 = getelementptr inbounds i8, i8* %24, i64 %26
store i8 49, i8* %27
br label %28
28: ; preds = %23, %11
br label %29
29: ; preds = %28
%30 = load i32, i32* %5
%31 = add nsw i32 %30, 1
store i32 %31, i32* %5
br label %8
32: ; preds = %8
ret void
}

LLVM IR (-O2):
define void @decomp(i8 signext %0, i8* nocapture writeonly %1) {
%3 = zext i8 %0 to i32
%4 = insertelement <8 x i32> poison, i32 %3, i64 0
%5 = shufflevector <8 x i32> %4, <8 x i32> poison, <8 x i32> zeroinitializer
%6 = and <8 x i32> %5, <i32 1, i32 2, i32 4, i32 8, i32 16, i32 32, i32 64, i32 128>
%7 = icmp eq <8 x i32> %6, zeroinitializer
%8 = extractelement <8 x i1> %7, i64 7
%9 = select i1 %8, i8 48, i8 49
store i8 %9, i8* %1
%10 = getelementptr inbounds i8, i8* %1, i64 1
%11 = extractelement <8 x i1> %7, i64 6
%12 = select i1 %11, i8 48, i8 49
store i8 %12, i8* %10
%13 = getelementptr inbounds i8, i8* %1, i64 2
%14 = extractelement <8 x i1> %7, i64 5
%15 = select i1 %14, i8 48, i8 49
store i8 %15, i8* %13
%16 = getelementptr inbounds i8, i8* %1, i64 3
%17 = extractelement <8 x i1> %7, i64 4
%18 = select i1 %17, i8 48, i8 49
store i8 %18, i8* %16
%19 = getelementptr inbounds i8, i8* %1, i64 4
%20 = extractelement <8 x i1> %7, i64 3
%21 = select i1 %20, i8 48, i8 49
store i8 %21, i8* %19
%22 = getelementptr inbounds i8, i8* %1, i64 5
%23 = extractelement <8 x i1> %7, i64 2
%24 = select i1 %23, i8 48, i8 49
store i8 %24, i8* %22
%25 = getelementptr inbounds i8, i8* %1, i64 6
%26 = extractelement <8 x i1> %7, i64 1
%27 = select i1 %26, i8 48, i8 49
store i8 %27, i8* %25
%28 = getelementptr inbounds i8, i8* %1, i64 7
%29 = extractelement <8 x i1> %7, i64 0
%30 = select i1 %29, i8 48, i8 49
store i8 %30, i8* %28
ret void
}