erts: Remove hashmap probabilistic heap overestimation

by adding a dynamic heap factory.

"binary_to_term" is now a hybrid solution with both
a call to decoded_size() to calculate needed heap space
AND possible dynamic allocation of more heap space
if needed for big maps.

The heap size returned from decoded_size() is guaranteed
to be sufficient for all term heap data except for hashmap
nodes. All hashmap nodes are created at the end of dec_term()
by invoking the heap factory interface that may allocate more
heap space on process heap or in fragments.

With this commit it is no longer guaranteed that a message
is confined to only one heap fragment.

1 files changed, 1 insertions, 0 deletions

diff --git a/erts/emulator/beam/big.h b/erts/emulator/beam/big.h
index 4e4611de16..5b5550da43 100644
--- a/erts/emulator/beam/big.h
+++ b/erts/emulator/beam/big.h
@@ -85,6 +85,7 @@ typedef Uint  dsize_t;	 /* Vector size type */
 
 /* The heap size needed for a bignum */
 #define BIG_NEED_SIZE(x)  ((x) + 1)
+#define BIG_NEED_FOR_BITS(bits) BIG_NEED_SIZE(((bits)-1)/D_EXP + 1)
 
 #define BIG_UINT_HEAP_SIZE (1 + 1)	/* always, since sizeof(Uint) <= sizeof(Eterm) */