float revert_(t)
char *t;
{
  char *alph64 =
      "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-";
  static int revmap[256], init = 1;
  static double exp[64] = {
      1e-36, 1e-35, 1e-34, 1e-33, 1e-32, 1e-31, 1e-30, 1e-29, 1e-28, 1e-27,
      1e-26, 1e-25, 1e-24, 1e-23, 1e-22, 1e-21, 1e-20, 1e-19, 1e-18, 1e-17,
      1e-16, 1e-15, 1e-14, 1e-13, 1e-12, 1e-11, 1e-10, 1e-09, 1e-08, 1e-07,
      1e-06, 1e-05, 1e-04, 1e-03, 1e-02, 1e-01, 1e+00, 1e+01, 1e+02, 1e+03,
      1e+04, 1e+05, 1e+06, 1e+07, 1e+08, 1e+09, 1e+10, 1e+11, 1e+12, 1e+13,
      1e+14, 1e+15, 1e+16, 1e+17, 1e+18, 1e+19, 1e+20, 1e+21, 1e+22, 1e+23,
      1e+24, 1e+25, 1e+26, 1e+27};
  register int mantis, i;
  float retval;
  if (init) {
    for (i = 0; i < 64; i++)
      revmap[alph64[i]] = i;
    init = 0;
  }
  mantis =
      ((((revmap[t[0]] << 6) | revmap[t[1]]) << 6) | revmap[t[2]]) - 131072;
  retval = (double)mantis * exp[revmap[t[3]]];
  return retval;
}


x86 assembly (clang, -O0):
<revert_>:
push   %rbp
mov    %rsp,%rbp
mov    %rdi,-0x8(%rbp)
lea    0xef1(%rip),%rax
mov    %rax,-0x10(%rbp)
cmpl   $0x0,0x2f16(%rip)
je     1163 <revert_+0x63>
movl   $0x0,-0x18(%rbp)
cmpl   $0x40,-0x18(%rbp)
jge    1159 <revert_+0x59>
mov    -0x18(%rbp),%edx
mov    -0x10(%rbp),%rax
movslq -0x18(%rbp),%rcx
movsbq (%rax,%rcx,1),%rcx
lea    0x3108(%rip),%rax
mov    %edx,(%rax,%rcx,4)
mov    -0x18(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x18(%rbp)
jmp    1127 <revert_+0x27>
movl   $0x0,0x2ecd(%rip)
mov    -0x8(%rbp),%rax
movsbq (%rax),%rcx
lea    0x30de(%rip),%rax
mov    (%rax,%rcx,4),%eax
shl    $0x6,%eax
mov    -0x8(%rbp),%rcx
movsbq 0x1(%rcx),%rdx
lea    0x30c8(%rip),%rcx
or     (%rcx,%rdx,4),%eax
shl    $0x6,%eax
mov    -0x8(%rbp),%rcx
movsbq 0x2(%rcx),%rdx
lea    0x30b2(%rip),%rcx
or     (%rcx,%rdx,4),%eax
sub    $0x20000,%eax
mov    %eax,-0x14(%rbp)
cvtsi2sdl -0x14(%rbp),%xmm0
mov    -0x8(%rbp),%rax
movsbq 0x3(%rax),%rcx
lea    0x3092(%rip),%rax
movslq (%rax,%rcx,4),%rcx
lea    0x2e77(%rip),%rax
mulsd  (%rax,%rcx,8),%xmm0
cvtsd2ss %xmm0,%xmm0
movss  %xmm0,-0x1c(%rbp)
movss  -0x1c(%rbp),%xmm0
pop    %rbp
ret

x86 assembly (clang, -O2):
<revert_>:
cmpb   $0x0,0x3329(%rip)
jne    115d <revert_+0x5d>
xor    %eax,%eax
lea    0xeee(%rip),%r8
lea    0x2f17(%rip),%rdx
nopl   0x0(%rax)
movsbq (%rax,%r8,1),%rsi
mov    %eax,(%rdx,%rsi,4)
movsbq 0x1(%rax,%r8,1),%rsi
lea    0x1(%rax),%ecx
mov    %ecx,(%rdx,%rsi,4)
movsbq 0x2(%rax,%r8,1),%rcx
lea    0x2(%rax),%esi
mov    %esi,(%rdx,%rcx,4)
movsbq 0x3(%rax,%r8,1),%rcx
lea    0x3(%rax),%esi
mov    %esi,(%rdx,%rcx,4)
add    $0x4,%rax
cmp    $0x40,%rax
jne    1120 <revert_+0x20>
movb   $0x1,0x32d3(%rip)
movsbq (%rdi),%rax
lea    0x2ec8(%rip),%rcx
mov    (%rcx,%rax,4),%eax
movsbq 0x1(%rdi),%rdx
mov    (%rcx,%rdx,4),%edx
shl    $0xc,%eax
shl    $0x6,%edx
or     %eax,%edx
movsbq 0x2(%rdi),%rax
or     (%rcx,%rax,4),%edx
add    $0xfffe0000,%edx
cvtsi2sd %edx,%xmm0
movsbq 0x3(%rdi),%rax
movslq (%rcx,%rax,4),%rax
lea    0xeb3(%rip),%rcx
mulsd  (%rcx,%rax,8),%xmm0
cvtsd2ss %xmm0,%xmm0
ret

LLVM IR (-O0):
@.str = [65 x i8] c"1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-\00"
@revert_.revmap = internal global [256 x i32] zeroinitializer
@revert_.init = internal global i32 1
@revert_.exp = internal global [64 x double] [double 0x38754484932D2E72, double 1.000000e-35, double 0x38E09D8792FB4C49, double 1.000000e-33, double 1.000000e-32, double 1.000000e-31, double 1.000000e-30, double 0x39E95A5EFEA6B347, double 1.000000e-28, double 1.000000e-27, double 1.000000e-26, double 1.000000e-25, double 0x3AF357C299A88EA7, double 0x3B282DB34012B251, double 1.000000e-22, double 0x3B92E3B40A0E9B4F, double 0x3BC79CA10C924223, double 0x3BFD83C94FB6D2AC, double 1.000000e-18, double 1.000000e-17, double 0x3C9CD2B297D889BC, double 1.000000e-15, double 0x3D06849B86A12B9B, double 1.000000e-13, double 0x3D719799812DEA11, double 0x3DA5FD7FE1796495, double 1.000000e-10, double 1.000000e-09, double 1.000000e-08, double 0x3E7AD7F29ABCAF48, double 0x3EB0C6F7A0B5ED8D, double 1.000000e-05, double 1.000000e-04, double 1.000000e-03, double 1.000000e-02, double 1.000000e-01, double 1.000000e+00, double 1.000000e+01, double 1.000000e+02, double 1.000000e+03, double 1.000000e+04, double 1.000000e+05, double 1.000000e+06, double 1.000000e+07, double 1.000000e+08, double 1.000000e+09, double 1.000000e+10, double 1.000000e+11, double 1.000000e+12, double 1.000000e+13, double 1.000000e+14, double 1.000000e+15, double 1.000000e+16, double 1.000000e+17, double 1.000000e+18, double 1.000000e+19, double 1.000000e+20, double 1.000000e+21, double 1.000000e+22, double 0x44B52D02C7E14AF6, double 0x44EA784379D99DB4, double 1.000000e+25, double 1.000000e+26, double 1.000000e+27]
define float @revert_(i8* %0) {
%2 = alloca i8*
%3 = alloca i8*
%4 = alloca i32
%5 = alloca i32
%6 = alloca float
store i8* %0, i8** %2
store i8* getelementptr inbounds ([65 x i8], [65 x i8]* @.str, i64 0, i64 0), i8** %3
%7 = load i32, i32* @revert_.init
%8 = icmp ne i32 %7, 0
br i1 %8, label %9, label %26
9: ; preds = %1
store i32 0, i32* %5
br label %10
10: ; preds = %22, %9
%11 = load i32, i32* %5
%12 = icmp slt i32 %11, 64
br i1 %12, label %13, label %25
13: ; preds = %10
%14 = load i32, i32* %5
%15 = load i8*, i8** %3
%16 = load i32, i32* %5
%17 = sext i32 %16 to i64
%18 = getelementptr inbounds i8, i8* %15, i64 %17
%19 = load i8, i8* %18
%20 = sext i8 %19 to i64
%21 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %20
store i32 %14, i32* %21
br label %22
22: ; preds = %13
%23 = load i32, i32* %5
%24 = add nsw i32 %23, 1
store i32 %24, i32* %5
br label %10
25: ; preds = %10
store i32 0, i32* @revert_.init
br label %26
26: ; preds = %25, %1
%27 = load i8*, i8** %2
%28 = getelementptr inbounds i8, i8* %27, i64 0
%29 = load i8, i8* %28
%30 = sext i8 %29 to i64
%31 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %30
%32 = load i32, i32* %31
%33 = shl i32 %32, 6
%34 = load i8*, i8** %2
%35 = getelementptr inbounds i8, i8* %34, i64 1
%36 = load i8, i8* %35
%37 = sext i8 %36 to i64
%38 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %37
%39 = load i32, i32* %38
%40 = or i32 %33, %39
%41 = shl i32 %40, 6
%42 = load i8*, i8** %2
%43 = getelementptr inbounds i8, i8* %42, i64 2
%44 = load i8, i8* %43
%45 = sext i8 %44 to i64
%46 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %45
%47 = load i32, i32* %46
%48 = or i32 %41, %47
%49 = sub nsw i32 %48, 131072
store i32 %49, i32* %4
%50 = load i32, i32* %4
%51 = sitofp i32 %50 to double
%52 = load i8*, i8** %2
%53 = getelementptr inbounds i8, i8* %52, i64 3
%54 = load i8, i8* %53
%55 = sext i8 %54 to i64
%56 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %55
%57 = load i32, i32* %56
%58 = sext i32 %57 to i64
%59 = getelementptr inbounds [64 x double], [64 x double]* @revert_.exp, i64 0, i64 %58
%60 = load double, double* %59
%61 = fmul double %51, %60
%62 = fptrunc double %61 to float
store float %62, float* %6
%63 = load float, float* %6
ret float %63
}

LLVM IR (-O2):
@.str = [65 x i8] c"1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-\00"
@revert_.revmap = internal unnamed_addr global [256 x i32] zeroinitializer
@revert_.init = internal unnamed_addr global i1 false
@revert_.exp = internal unnamed_addr constant [64 x double] [double 0x38754484932D2E72, double 1.000000e-35, double 0x38E09D8792FB4C49, double 1.000000e-33, double 1.000000e-32, double 1.000000e-31, double 1.000000e-30, double 0x39E95A5EFEA6B347, double 1.000000e-28, double 1.000000e-27, double 1.000000e-26, double 1.000000e-25, double 0x3AF357C299A88EA7, double 0x3B282DB34012B251, double 1.000000e-22, double 0x3B92E3B40A0E9B4F, double 0x3BC79CA10C924223, double 0x3BFD83C94FB6D2AC, double 1.000000e-18, double 1.000000e-17, double 0x3C9CD2B297D889BC, double 1.000000e-15, double 0x3D06849B86A12B9B, double 1.000000e-13, double 0x3D719799812DEA11, double 0x3DA5FD7FE1796495, double 1.000000e-10, double 1.000000e-09, double 1.000000e-08, double 0x3E7AD7F29ABCAF48, double 0x3EB0C6F7A0B5ED8D, double 1.000000e-05, double 1.000000e-04, double 1.000000e-03, double 1.000000e-02, double 1.000000e-01, double 1.000000e+00, double 1.000000e+01, double 1.000000e+02, double 1.000000e+03, double 1.000000e+04, double 1.000000e+05, double 1.000000e+06, double 1.000000e+07, double 1.000000e+08, double 1.000000e+09, double 1.000000e+10, double 1.000000e+11, double 1.000000e+12, double 1.000000e+13, double 1.000000e+14, double 1.000000e+15, double 1.000000e+16, double 1.000000e+17, double 1.000000e+18, double 1.000000e+19, double 1.000000e+20, double 1.000000e+21, double 1.000000e+22, double 0x44B52D02C7E14AF6, double 0x44EA784379D99DB4, double 1.000000e+25, double 1.000000e+26, double 1.000000e+27]
define float @revert_(i8* nocapture %0) {
%2 = load i1, i1* @revert_.init
br i1 %2, label %31, label %3
3: ; preds = %1, %3
%4 = phi i64 [ %28, %3 ], [ 0, %1 ]
%5 = getelementptr inbounds [65 x i8], [65 x i8]* @.str, i64 0, i64 %4
%6 = load i8, i8* %5
%7 = sext i8 %6 to i64
%8 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %7
%9 = trunc i64 %4 to i32
store i32 %9, i32* %8
%10 = or i64 %4, 1
%11 = getelementptr inbounds [65 x i8], [65 x i8]* @.str, i64 0, i64 %10
%12 = load i8, i8* %11
%13 = sext i8 %12 to i64
%14 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %13
%15 = trunc i64 %10 to i32
store i32 %15, i32* %14
%16 = or i64 %4, 2
%17 = getelementptr inbounds [65 x i8], [65 x i8]* @.str, i64 0, i64 %16
%18 = load i8, i8* %17
%19 = sext i8 %18 to i64
%20 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %19
%21 = trunc i64 %16 to i32
store i32 %21, i32* %20
%22 = or i64 %4, 3
%23 = getelementptr inbounds [65 x i8], [65 x i8]* @.str, i64 0, i64 %22
%24 = load i8, i8* %23
%25 = sext i8 %24 to i64
%26 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %25
%27 = trunc i64 %22 to i32
store i32 %27, i32* %26
%28 = add nuw nsw i64 %4, 4
%29 = icmp eq i64 %28, 64
br i1 %29, label %30, label %3
30: ; preds = %3
store i1 true, i1* @revert_.init
br label %31
31: ; preds = %30, %1
%32 = load i8, i8* %0
%33 = sext i8 %32 to i64
%34 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %33
%35 = load i32, i32* %34
%36 = getelementptr inbounds i8, i8* %0, i64 1
%37 = load i8, i8* %36
%38 = sext i8 %37 to i64
%39 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %38
%40 = load i32, i32* %39
%41 = shl i32 %35, 12
%42 = shl i32 %40, 6
%43 = or i32 %42, %41
%44 = getelementptr inbounds i8, i8* %0, i64 2
%45 = load i8, i8* %44
%46 = sext i8 %45 to i64
%47 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %46
%48 = load i32, i32* %47
%49 = or i32 %43, %48
%50 = add nsw i32 %49, -131072
%51 = sitofp i32 %50 to double
%52 = getelementptr inbounds i8, i8* %0, i64 3
%53 = load i8, i8* %52
%54 = sext i8 %53 to i64
%55 = getelementptr inbounds [256 x i32], [256 x i32]* @revert_.revmap, i64 0, i64 %54
%56 = load i32, i32* %55
%57 = sext i32 %56 to i64
%58 = getelementptr inbounds [64 x double], [64 x double]* @revert_.exp, i64 0, i64 %57
%59 = load double, double* %58
%60 = fmul double %59, %51
%61 = fptrunc double %60 to float
ret float %61
}