From: H.G.Muller <hgm@hgm-xboard.(none)>
Date: Sat, 3 Jan 2026 21:11:24 +0000 (+0100)
Subject: Let Betza parser understand true riding
X-Git-Url: http://winboard.nl/cgi-bin?a=commitdiff_plain;h=8cb6a88dc7d6bac96ec8c1ad29b5c0dacd896d52;p=fairystockfish.git

Let Betza parser understand true riding

Riding moves like DD or AA were accepted by the Betza parser, but did not
work because no magics for those moves were available. By using custom
rides derived from the R and B masks then now do work: their basic leap
is reduced to a single step, but the squares they are supposed to skip are
then masked out of their magics mask and their pseudoAttacks.
  This allows specification of moves that ride along Queen rays with
stride 2 or 3. (So AA, DD, HH and GG.) Lame versions of these (e.g. nDD)
are also available: these would only mask the squares to be skipped out
of the pseudoAttacks, and use those with ordinary Rook and Bishop magics
which can still be blocked on those squares.
---

diff --git a/src/piece.cpp b/src/piece.cpp
index f6ad675..82a4117 100644
--- a/src/piece.cpp
+++ b/src/piece.cpp
@@ -141,6 +141,15 @@ namespace {
                   int y = atom.first + 3*fExtension + 2*fsExtension;
                   int x = atom.second + 2*fsExtension;
                   std::vector<std::string> directions = {};
+                  if(rider && y > 1 && (x == 0 || x == y)) { // radial true rider
+                      for(int n = distance; ~n & 1; n >>= 1) distance <<= y - 1; // adapt range to larger stride
+                      distance &= 0xFFFF;
+                      if(y == 2) distance |= 0x55555555; else
+                      if(y == 3) distance |= 0xB6DBB6DB; else
+                      if(y == 4) distance |= 0x77777777;
+                      if(lame) distance &= 0xFFFF;
+                      x /= y; y = 1; // use (masked) slider magics
+                  }
                   // Split directions for orthogonal pieces
                   // This is required e.g. to correctly interpret fsW for soldiers
                   for (auto s : prelimDirections)