Bug 516862: Backported a change from dtoa.c upstream made on 2009-03-01. [r=crowder r=mrbkap]

Here is an excerpt from the 'changes' file describing this change:
"dtoa.c and gdtoa/gdtoaimp.h and gdtoa/misc.c: reduce Kmax, and use
MALLOC and FREE or free for huge blocks, which are possible only in
pathological cases, such as dtoa calls in mode 3 with thousands of
digits requested, or strtod() calls with thousand of digits. For the
latter case, I have an alternate approach that runs much faster
and uses less memory, but finding time to get it ready for distribution
may take a while."

js/src/dtoa.c

@@ -98,7 +98,12 @@
  * #define MALLOC your_malloc, where your_malloc(n) acts like malloc(n)
  *	if memory is available and otherwise does something you deem
  *	appropriate.  If MALLOC is undefined, malloc will be invoked
- *	directly -- and assumed always to succeed.
+ *	directly -- and assumed always to succeed.  Similarly, if you
+ *	want something other than the system's free() to be called to
+ *	recycle memory acquired from MALLOC, #define FREE to be the
+ *	name of the alternate routine.  (FREE or free is only called in
+ *	pathological cases, e.g., in a dtoa call after a dtoa return in
+ *	mode 3 with thousands of digits requested.)
  * #define Omit_Private_Memory to omit logic (added Jan. 1998) for making
  *	memory allocations from a private pool of memory when possible.
  *	When used, the private pool is PRIVATE_MEM bytes long:  2304 bytes,
@@ -463,7 +468,7 @@ extern double rnd_prod(double, double), rnd_quot(double, double);
 #define FREE_DTOA_LOCK(n)	/*nothing*/
 #endif
 
-#define Kmax 15
+#define Kmax 7
 
  struct
 Bigint {
@@ -491,9 +496,10 @@ Balloc
 #endif
 
 	ACQUIRE_DTOA_LOCK(0);
-	if ((rv = freelist[k])) {
+	/* The k > Kmax case does not need ACQUIRE_DTOA_LOCK(0), */
+	/* but this case seems very unlikely. */
+	if (k <= Kmax && (rv = freelist[k]))
 		freelist[k] = rv->next;
-		}
 	else {
 		x = 1 << k;
 #ifdef Omit_Private_Memory
@@ -501,7 +507,7 @@ Balloc
 #else
 		len = (sizeof(Bigint) + (x-1)*sizeof(ULong) + sizeof(double) - 1)
 			/sizeof(double);
-		if (pmem_next - private_mem + len <= PRIVATE_mem) {
+		if (k <= Kmax && pmem_next - private_mem + len <= PRIVATE_mem) {
 			rv = (Bigint*)pmem_next;
 			pmem_next += len;
 			}
@@ -525,10 +531,18 @@ Bfree
 #endif
 {
 	if (v) {
-		ACQUIRE_DTOA_LOCK(0);
-		v->next = freelist[v->k];
-		freelist[v->k] = v;
-		FREE_DTOA_LOCK(0);
+		if (v->k > Kmax)
+#ifdef FREE
+			FREE((void*)v);
+#else
+			free((void*)v);
+#endif
+		else {
+			ACQUIRE_DTOA_LOCK(0);
+			v->next = freelist[v->k];
+			freelist[v->k] = v;
+			FREE_DTOA_LOCK(0);
+			}
 		}
 	}