FEAT: optimize powerof2 memory allocation

Author: Oldes

src/core/m-pools.c

@@ -411,11 +411,7 @@ const REBPOOLSPEC Mem_Pool_Spec[MAX_POOLS] =
 #endif
 	} else {
 		if (powerof2) {
-			// !!! WHO added this and why??? Just use a left shift and mask!
-			REBCNT len=2048;
-			while(len<length)
-				len*=2;
-			length=len;
+			U32_ROUND_UP_POWER_OF_2(length);
 		} else
 			length = ALIGN(length, 2048);
 #ifdef DEBUGGING

src/include/reb-c.h

@@ -306,6 +306,16 @@ typedef void(*CFUNC)(void *);
 
 #define ROUND_TO_INT(d) (REBINT)(floor((d) + 0.5))
 
+// https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
+// Note: 32bit, v must be > 0
+#define U32_ROUND_UP_POWER_OF_2(v) \
+                    v--;           \
+                    v |= v >> 1;   \
+                    v |= v >> 2;   \
+                    v |= v >> 4;   \
+                    v |= v >> 8;   \
+                    v |= v >> 16;  \
+                    v++;           \
 
 /***********************************************************************
 **