From 8b57c494908637a5c0e74f8f7a13b3218e026757 Mon Sep 17 00:00:00 2001
From: Jeffrey Wilcke <jeffrey@ethereum.org>
Date: Thu, 2 Feb 2017 15:25:42 +0100
Subject: params: core, core/vm, miner: 64bit gas instructions (#3514)

Reworked the EVM gas instructions to use 64bit integers rather than
arbitrary size big ints. All gas operations, be it additions,
multiplications or divisions, are checked and guarded against 64 bit
integer overflows.

In additon, most of the protocol paramaters in the params package have
been converted to uint64 and are now constants rather than variables.

* common/math: added overflow check ops
* core: vmenv, env renamed to evm
* eth, internal/ethapi, les: unmetered eth_call and cancel methods
* core/vm: implemented big.Int pool for evm instructions
* core/vm: unexported intPool methods & verification methods
* core/vm: added memoryGasCost overflow check and test
---
 common/math/integer.go      | 25 +++++++++++++++++++++++
 common/math/integer_test.go | 50 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)
 create mode 100644 common/math/integer.go
 create mode 100644 common/math/integer_test.go

(limited to 'common')

diff --git a/common/math/integer.go b/common/math/integer.go
new file mode 100644
index 000000000..8162b1985
--- /dev/null
+++ b/common/math/integer.go
@@ -0,0 +1,25 @@
+package math
+
+import gmath "math"
+
+/*
+ * NOTE: The following methods need to be optimised using either bit checking or asm
+ */
+
+// SafeSub returns subtraction result and whether overflow occurred.
+func SafeSub(x, y uint64) (uint64, bool) {
+	return x - y, x < y
+}
+
+// SafeAdd returns the result and whether overflow occurred.
+func SafeAdd(x, y uint64) (uint64, bool) {
+	return x + y, y > gmath.MaxUint64-x
+}
+
+// SafeMul returns multiplication result and whether overflow occurred.
+func SafeMul(x, y uint64) (uint64, bool) {
+	if x == 0 {
+		return 0, false
+	}
+	return x * y, x != 0 && y != 0 && y > gmath.MaxUint64/x
+}
diff --git a/common/math/integer_test.go b/common/math/integer_test.go
new file mode 100644
index 000000000..198114e5e
--- /dev/null
+++ b/common/math/integer_test.go
@@ -0,0 +1,50 @@
+package math
+
+import (
+	gmath "math"
+	"testing"
+)
+
+type operation byte
+
+const (
+	sub operation = iota
+	add
+	mul
+)
+
+func TestOverflow(t *testing.T) {
+	for i, test := range []struct {
+		x        uint64
+		y        uint64
+		overflow bool
+		op       operation
+	}{
+		// add operations
+		{gmath.MaxUint64, 1, true, add},
+		{gmath.MaxUint64 - 1, 1, false, add},
+
+		// sub operations
+		{0, 1, true, sub},
+		{0, 0, false, sub},
+
+		// mul operations
+		{10, 10, false, mul},
+		{gmath.MaxUint64, 2, true, mul},
+		{gmath.MaxUint64, 1, false, mul},
+	} {
+		var overflows bool
+		switch test.op {
+		case sub:
+			_, overflows = SafeSub(test.x, test.y)
+		case add:
+			_, overflows = SafeAdd(test.x, test.y)
+		case mul:
+			_, overflows = SafeMul(test.x, test.y)
+		}
+
+		if test.overflow != overflows {
+			t.Errorf("%d failed. Expected test to be %v, got %v", i, test.overflow, overflows)
+		}
+	}
+}
-- 
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