Fix missing _BitScanForward64 on Windows x86

Fixes #220.
foonathan · Jan 7, 2025 · 21728ab · 21728ab
1 parent 0bce9a7
commit 21728ab
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Showing 2 changed files with 8 additions and 3 deletions.
diff --git a/include/lexy/_detail/swar.hpp b/include/lexy/_detail/swar.hpp
@@ -139,10 +139,14 @@ constexpr std::size_t swar_find_difference(swar_int lhs, swar_int rhs)
 
 #if defined(__GNUC__)
     auto bit_idx = __builtin_ctzll(mask);
-#elif defined(_MSC_VER)
+#elif defined(_MSC_VER) && defined(_WIN64)
     unsigned long bit_idx;
-    if (!_BitScanForward64(&bit_idx, mask))
-        bit_idx = 64;
+    _BitScanForward64(&bit_idx, mask);
+#elif defined(_MSC_VER)
+    unsigned long bit_idx = 0;
+    if (!_BitScanForward(&bit_idx, static_cast<std::uint32_t>(mask))
+        && _BitScanForward(&bit_idx, mask >> 32))
+        bit_idx += 32;
 #else
 #    error "unsupported compiler; please file an issue"
 #endif

diff --git a/tests/lexy/detail/swar.cpp b/tests/lexy/detail/swar.cpp
@@ -74,6 +74,7 @@ TEST_CASE("swar_find_difference")
     CHECK(swar_find_difference<char>(a, a) == 8);
     CHECK(swar_find_difference<char>(a, A) == 0);
     CHECK(swar_find_difference<char>(abc, aBc) == 1);
+    CHECK(swar_find_difference<char>(0x1'FFFF'FFFF, 0x2'FFFF'FFFF) == 4);
 }
 
 TEST_CASE("swar_has_zero")