Add size class computation capability.

Add size class computation capability, currently used only as validation
of the size class lookup tables.  Generalize the size class spacing used
for bins, for eventual use throughout the full range of allocation
sizes.

include/jemalloc/internal/util.h

@@ -110,6 +110,7 @@ void	malloc_printf(const char *format, ...)
 
 #ifndef JEMALLOC_ENABLE_INLINE
 size_t	pow2_ceil(size_t x);
+size_t	lg_floor(size_t x);
 void	set_errno(int errnum);
 int	get_errno(void);
 #endif
@@ -133,6 +134,52 @@ pow2_ceil(size_t x)
 	return (x);
 }
 
+#if (defined(__i386__) || defined(__amd64__) || defined(__x86_64__))
+JEMALLOC_INLINE size_t
+lg_floor(size_t x)
+{
+	size_t ret;
+
+	asm ("bsr %1, %0"
+	    : "=r"(ret) // Outputs.
+	    : "r"(x)    // Inputs.
+	    );
+	return (ret);
+}
+#elif (defined(JEMALLOC_HAVE_BUILTIN_CLZ))
+JEMALLOC_INLINE size_t
+lg_floor(size_t x)
+{
+
+#if (LG_SIZEOF_PTR == LG_SIZEOF_INT)
+	return ((8 << LG_SIZEOF_PTR - 1) - __builtin_clz(x));
+#elif (LG_SIZEOF_PTR == LG_SIZEOF_LONG)
+	return ((8 << LG_SIZEOF_PTR - 1) - __builtin_clzl(x));
+#else
+#  error "Unsupported type sizes for lg_floor()"
+#endif
+}
+#else
+JEMALLOC_INLINE size_t
+lg_floor(size_t x)
+{
+
+        x |= (x >> 1);
+        x |= (x >> 2);
+        x |= (x >> 4);
+        x |= (x >> 8);
+        x |= (x >> 16);
+#if (LG_SIZEOF_PTR == 3 && LG_SIZEOF_PTR == LG_SIZEOF_LONG)
+        x |= (x >> 32);
+        return (65 - ffsl(~x));
+#elif (LG_SIZEOF_PTR == 2)
+        return (33 - ffs(~x));
+#else
+#  error "Unsupported type sizes for lg_floor()"
+#endif
+}
+#endif
+
 /* Sets error code */
 JEMALLOC_INLINE void
 set_errno(int errnum)