Add functions to round to nearest power of 2

diff --git a/src/lib/util/math.h b/src/lib/util/math.h
index ddf80a670a652654abb1bf19c867503ef3a0a911..b7b755087d6daab1d81f5beb6d589f1744729406 100644 (file)
--- a/src/lib/util/math.h
+++ b/src/lib/util/math.h
@@ -23,10 +23,68 @@
  */
 RCSIDH(math_h, "$Id$")
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+static inline uint64_t fr_roundup_pow2_uint64(uint64_t v)
+{
+#ifdef HAVE_BUILTIN_CLZLL
+       if (v <= 1) return 1;
+       return 1ULL << (64 - __builtin_clzll(v - 1));
+#else
+       if (v == 0) return 1;
+       v--;
+       v |= v >> 1;
+       v |= v >> 2;
+       v |= v >> 4;
+       v |= v >> 8;
+       v |= v >> 16;
+       v |= v >> 32;
+       v++;
+       return v;
+#endif
+}
+
+static inline int64_t fr_roundup_pow2_int64(int64_t v)
+{
+       uint64_t uv;
+
+       if (v <= 1) return 1;
+
+#ifdef HAVE_BUILTIN_CLZLL
+       uv = (uint64_t)(v - 1);
+
+       {
+               int shift = 64 - __builtin_clzll(uv);
+
+               if (shift >= 63) {
+                       // would exceed INT64_MAX
+                       return 0;
+               }
+               return (int64_t)(1ULL << shift);
+       }
+#else
+       uv = (uint64_t)v;
+       uv--;
+
+       uv |= uv >> 1;
+       uv |= uv >> 2;
+       uv |= uv >> 4;
+       uv |= uv >> 8;
+       uv |= uv >> 16;
+       uv |= uv >> 32;
+       uv++;
+
+       if (uv > (uint64_t)INT64_MAX) {
+               return 0;
+       }
+       return (int64_t)uv;
+#endif
+}
+
 /** Find the highest order high bit in an unsigned 64 bit integer
  *
  * @return 0-64 indicating the position of the highest bit,