new file mode 100644

@@ -0,0 +1,65 @@

+#include <array>

+#include <cstdint>

+#include <cstdio>

+#include <cstdlib>

+#include <fstream>

+#include <iostream>

+#include <vector>

+

+void um(std::istream & scroll, std::istream & i, std::ostream & o)

+{

+    std::unitbuf(o);

+    using Chr   = std::uint8_t;

+    using Plt   = std::uint32_t;

+    auto  reg   = std::array<Plt, 8>();

+    auto  arr   = std::vector<std::vector<Plt>>(1);

+    auto  fng   = Plt(0);

+    auto  hlt   = false;

+    auto  alloc = [&](Plt c) { arr.emplace_back(c); return(Plt)arr.size()-1; };

+    auto  aband = [&](Plt c) { arr[c] = decltype(arr)::value_type();         };

+    #define PACK(IND) ((Plt)(Chr)ch[IND] << 8*(3-IND))

+    for (char ch[4]; scroll.read(ch, 4);)

+        arr[0].push_back(PACK(0) | PACK(1) | PACK(2) | PACK(3));

+    #undef PACK

+    while (!hlt)

+    {

+        #define UNPACK(POS, SIZ) ((plt >> POS) & ((Plt(1) << SIZ) - 1))

+        auto   plt = arr[0][fng++];

+        auto   num =     UNPACK(28,  4);

+        auto   val =     UNPACK( 0, 25);

+        auto & a   = reg[UNPACK( 6,  3)];

+        auto & b   = reg[UNPACK( 3,  3)];

+        auto & c   = reg[UNPACK( 0,  3)];

+        auto & d   = reg[UNPACK(25,  3)];

+        #undef UNPACK

+        switch (num)

+        {

+            case  0: a         = c ? b : a;       break; // CMOVE

+            case  1: a         = arr[b][c];       break; // LOAD

+            case  2: arr[a][b] = c;               break; // STOR

+            case  3: a         =   b + c;         break; // ADD

+            case  4: a         =   b * c;         break; // MUL

+            case  5: a         =   b / c;         break; // DIV

+            case  6: a         = ~(b & c);        break; // NAND

+            case  7: hlt       = true;            break; // HALT

+            case  8: b         = alloc(c);        break; // ALLOC

+            case  9:             aband(c);        break; // ABAND

+            case 10:             o.put(c);        break; // PUT

+            case 11: c         = i.get();         break; // GET

+            case 12: arr[0]    = arr[b]; fng = c; break; // EXEC

+            case 13: d         = val;             break; // VALUE

+        }

+    }

+}

+

+int main(int argc, char * argv[])

+{

+    if (argc != 2)

+        return std::fputs("Usage: um <scroll>\n", stderr), EXIT_FAILURE;

+    auto scroll = std::ifstream(argv[1], std::ios::binary);

+    if (scroll.fail())

+        return std::perror("Failed to read scroll"), EXIT_FAILURE;

+    if (scroll.peek(), scroll.eof())

+        return std::fputs("Empty scroll\n", stderr), EXIT_FAILURE;

+    um(scroll, std::cin, std::cout);

+}