diff --git a/common/dlmalloc.c b/common/dlmalloc.c
index 83b1e18..ff63fbe 100644
--- a/common/dlmalloc.c
+++ b/common/dlmalloc.c
@@ -792,7 +792,7 @@
 #define IAV(i)  bin_at(i), bin_at(i)
 
 static mbinptr av_[NAV * 2 + 2] = {
-	0, 0,
+	NULL, NULL,
 	IAV (0), IAV (1), IAV (2), IAV (3), IAV (4), IAV (5), IAV (6), IAV (7),
 	IAV (8), IAV (9), IAV (10), IAV (11), IAV (12), IAV (13), IAV (14),
 	IAV (15),
@@ -1209,7 +1209,7 @@
 	INTERNAL_SIZE_T nb;
 
 	if ((long) bytes < 0)
-		return 0;
+		return NULL;
 
 	nb = request2size(bytes); /* padded request size; */
 
@@ -1364,7 +1364,7 @@
 		/* Try to extend */
 		malloc_extend_top(nb);
 		if ((remainder_size = chunksize(top) - nb) < (long) MINSIZE)
-			return 0;	/* propagate failure */
+			return NULL;	/* propagate failure */
 	}
 
 	victim = top;
@@ -1405,7 +1405,7 @@
 	mchunkptr fwd;		/* misc temp for linking */
 	int islr;		/* track whether merging with last_remainder */
 
-	if (mem == 0)		/* free(0) has no effect */
+	if (!mem)		/* free(0) has no effect */
 		return;
 
 	p = mem2chunk(mem);
@@ -1524,15 +1524,15 @@
 #ifdef REALLOC_ZERO_BYTES_FREES
 	if (bytes == 0) {
 		free(oldmem);
-		return 0;
+		return NULL;
 	}
 #endif
 
 	if ((long)bytes < 0)
-		return 0;
+		return NULL;
 
 	/* realloc of null is supposed to be same as malloc */
-	if (oldmem == 0)
+	if (!oldmem)
 		return malloc(bytes);
 
 	newp = oldp = mem2chunk(oldmem);
@@ -1570,7 +1570,7 @@
 				goto split;
 			}
 		} else {
-			next = 0;
+			next = NULL;
 			nextsize = 0;
 		}
 
@@ -1582,7 +1582,7 @@
 
 			/* try forward + backward first to save a later consolidation */
 
-			if (next != 0) {
+			if (next) {
 				/* into top */
 				if (next == top) {
 					if ((long)
@@ -1618,8 +1618,7 @@
 			}
 
 			/* backward only */
-			if (prev != 0
-			    && (long)(prevsize + newsize) >= (long)nb) {
+			if (prev && (long)(prevsize + newsize) >= (long)nb) {
 				unlink(prev, bck, fwd);
 				newp = prev;
 				newsize += prevsize;
@@ -1633,8 +1632,8 @@
 
 		newmem = malloc(bytes);
 
-		if (newmem == 0)	/* propagate failure */
-			return 0;
+		if (!newmem)	/* propagate failure */
+			return NULL;
 
 		/* Avoid copy if newp is next chunk after oldp. */
 		/* (This can only happen when new chunk is sbrk'ed.) */
@@ -1697,7 +1696,7 @@
 	long remainder_size;	/* its size */
 
 	if ((long) bytes < 0)
-		return 0;
+		return NULL;
 
 	/* If need less alignment than we give anyway, just relay to malloc */
 
@@ -1714,8 +1713,8 @@
 	nb = request2size(bytes);
 	m = (char*)(malloc (nb + alignment + MINSIZE));
 
-	if (m == 0)
-		return 0;	/* propagate failure */
+	if (!m)
+		return NULL;	/* propagate failure */
 
 	p = mem2chunk(m);
 
@@ -1763,6 +1762,7 @@
 	return chunk2mem(p);
 }
 
+#if 0
 /*
  * valloc just invokes memalign with alignment argument equal
  * to the page size of the system (or as near to this as can
@@ -1772,6 +1772,7 @@
 {
 	return memalign(malloc_getpagesize, bytes);
 }
+#endif
 
 /*
  * pvalloc just invokes valloc for the nearest pagesize
@@ -1802,10 +1803,10 @@
 	void *mem = malloc(sz);
 
 	if ((long)n < 0)
-		return 0;
+		return NULL;
 
-	if (mem == 0)
-		return 0;
+	if (!mem)
+		return NULL;
 	else {
 		p = mem2chunk(mem);
 
@@ -1915,7 +1916,7 @@
 {
 	mchunkptr p;
 
-	if (mem == 0)
+	if (!mem)
 		return 0;
 	else {
 		p = mem2chunk(mem);