Merge pull request #3674 from obscuren/gaz64

params: core, core/vm, miner: 64bit gas instructions

2 files changed, 75 insertions, 0 deletions

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)
+		}
+	}
+}