1 files changed, 29 insertions, 0 deletions

diff --git a/src/main.h b/src/main.h
index 382dd9c..30e25ef 100644
--- a/src/main.h
+++ b/src/main.h
@@ -33,6 +33,35 @@ static const unsigned int MAX_BLOCK_SIGOPS = 20000;
 // limit (32 MB), not a block rule. Bitcoin 0.1.0 predated the later 1 MB block
 // cap, so this tree inherited no real block-size consensus limit.
 static const unsigned int MAX_BLOCK_SIZE = 1000000;
+// How much of that cap a template we build may fill. Half, which is what both
+// assemblers already aimed at -- this only gives the number a name and one
+// place to live. They had already drifted on how it was enforced, which is the
+// bug this exists to stop repeating.
+//
+// NOT a consensus rule. CheckBlock() decides what the network accepts; this
+// decides what we are willing to produce, and it has to stay under that.
+static const unsigned int MAX_BLOCK_SIZE_GEN = MAX_BLOCK_SIZE / 2;
+
+// Room for one more transaction in a template that currently weighs
+// nBlockSize bytes and spends nBlockSigOps signature operations?
+//
+// Asked BEFORE the transaction is appended, never after. A template that has
+// already overshot is one CheckBlock() rejects, and asking afterwards only
+// measures the waste. Both assemblers call this, so neither can drift into a
+// different idea of what fits.
+//
+// Size gets a margin (half the cap); sigops do not. There is no cheap way to
+// spend the sigop budget usefully and no reason to reserve headroom in it, so
+// assembly holds itself to the same number CheckBlock() enforces -- and to the
+// same comparison. CheckBlock() fails on `> MAX_BLOCK_SIGOPS`, so a block
+// sitting exactly on the limit is valid and this has to accept it too.
+// Assembly and validation disagreeing by one is how the size bug started.
+inline bool BlockTemplateFits(unsigned int nBlockSize, unsigned int nBlockSigOps,
+                              unsigned int nTxSize, unsigned int nTxSigOps)
+{
+    return (nBlockSize + nTxSize <= MAX_BLOCK_SIZE_GEN &&
+            nBlockSigOps + nTxSigOps <= MAX_BLOCK_SIGOPS);
+}
 static const int64 COIN = 100000000;
 // Total Bitflash emission: identical to Bitcoin (21 million).
 // MAX_MONEY guards against the value overflow bug (CVE-2010-5139), which in