Update to bsnes v107r4 beta release.

byuu says:

  - bsnes: added video filters from bsnes v082
  - bsnes: added ZSNES snow effect option when games paused or unloaded
    (no, I'm not joking)
  - bsnes: added 7-zip support (LZMA 19.00 SDK)

[Recent higan WIPs have also mentioned bsnes changes, although the higan code
no longer includes the bsnes code. These changes include:

  - higan, bsnes: added EXLOROM, EXLOROM-RAM, EXHIROM mappings
  - higan, bsnes: focus the viewport after leaving fullscreen exclusive
    mode
  - bsnes: re-added mightymo's cheat code database
  - bsnes: improved make install rules for the game and cheat code
    databases
  - bsnes: delayed construction of hiro::Window objects to properly show
    bsnes window icons

- Ed.]

nall/cd/scrambler.hpp

@@ -0,0 +1,35 @@
+#pragma once
+
+namespace nall::CD::Scrambler {
+
+//polynomial(x) = x^15 + x + 1
+inline auto polynomial(uint x) -> uint8_t {
+  static uint8_t lookup[2340]{};
+  static bool once = false;
+  if(!once) { once = true;
+    uint16_t shift = 0x0001;
+    for(uint n : range(2340)) {
+      lookup[n] = shift;
+      for(uint b : range(8)) {
+        bool carry = shift & 1 ^ shift >> 1 & 1;
+        shift = (carry << 15 | shift) >> 1;
+      }
+    }
+  }
+  return lookup[x];
+}
+
+//
+
+inline auto transform(array_span<uint8_t> sector) -> bool {
+  if(sector.size() == 2352) sector += 12;  //header is not scrambled
+  if(sector.size() != 2340) return false;  //F1 frames only
+
+  for(uint index : range(2340)) {
+    sector[index] ^= polynomial(index);
+  }
+
+  return true;
+}
+
+}