1 files changed, 30 insertions, 1 deletions
diff --git a/src/nvim/math.c b/src/nvim/math.c
index 96ff1bef10..9a0825823c 100644
--- a/src/nvim/math.c
+++ b/src/nvim/math.c
@@ -7,10 +7,11 @@
 #include "nvim/math.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "math.c.generated.h"  // IWYU pragma: export
+# include "math.c.generated.h"
 #endif
 
 int xfpclassify(double d)
+  FUNC_ATTR_CONST
 {
   uint64_t m;
 
@@ -29,11 +30,39 @@ int xfpclassify(double d)
 }
 
 int xisinf(double d)
+  FUNC_ATTR_CONST
 {
   return FP_INFINITE == xfpclassify(d);
 }
 
 int xisnan(double d)
+  FUNC_ATTR_CONST
 {
   return FP_NAN == xfpclassify(d);
 }
+
+/// Count trailing zeroes at the end of bit field.
+int xctz(uint64_t x)
+{
+  // If x == 0, that means all bits are zeroes.
+  if (x == 0) {
+    return 8 * sizeof(x);
+  }
+
+  // Use compiler builtin if possible.
+#if defined(__clang__) || (defined(__GNUC__) && (__GNUC__ >= 4))
+  return __builtin_ctzll(x);
+#else
+  int count = 0;
+  // Set x's trailing zeroes to ones and zero the rest.
+  x = (x ^ (x - 1)) >> 1;
+
+  // Increment count until there are just zero bits remaining.
+  while (x) {
+    count++;
+    x >>= 1;
+  }
+
+  return count;
+#endif
+}