FEAT: optimize powerof2 memory allocation

Oldes · Sep 9, 2021 · 53167c3 · 53167c3
1 parent a7b95f3
commit 53167c3
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Showing 2 changed files with 11 additions and 5 deletions.
diff --git a/src/core/m-pools.c b/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

diff --git a/src/include/reb-c.h b/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++;           \
 
 /***********************************************************************
 **