ARM lsb/msb assembly

[stockfish] / src / bitboard.h

diff --git a/src/bitboard.h b/src/bitboard.h
index 4c7c948a8d28d0dfa9e8bc8c08f88471797b2b9d..6aa35874df7d3a244a8be9a919c81e09cc46105e 100644 (file)
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -247,6 +247,21 @@ FORCE_INLINE Square msb(Bitboard b) {
   return (Square) index;
 }
 
+#  elif defined(__arm__)
+
+FORCE_INLINE int lsb32(uint32_t v) {
+  __asm__("rbit %0, %1" : "=r"(v) : "r"(v));
+  return __builtin_clz(v);
+}
+
+FORCE_INLINE Square msb(Bitboard b) {
+  return (Square) (63 - __builtin_clzll(b));
+}
+
+FORCE_INLINE Square lsb(Bitboard b) {
+  return (Square) (uint32_t(b) ? lsb32(uint32_t(b)) : 32 + lsb32(uint32_t(b >> 32)));
+}
+
 #  else
 
 FORCE_INLINE Square lsb(Bitboard b) { // Assembly code by Heinz van Saanen