From f80c3255a34cea396f9bc6bec273c71505aa0616 Mon Sep 17 00:00:00 2001
From: "Owain G. Ainsworth" <oga@conformal.com>
Date: Fri, 14 Mar 2014 17:51:17 +0000
Subject: [PATCH] PopInt now guarantees that number will be 32 bit.

So remove later checks that need this.
---
 opcode.go      | 19 ++++---------------
 opcode_test.go |  5 +++--
 stack.go       | 14 +++++++++-----
 3 files changed, 16 insertions(+), 22 deletions(-)

diff --git a/opcode.go b/opcode.go
index 58ec7367..52b930b9 100644
--- a/opcode.go
+++ b/opcode.go
@@ -1258,10 +1258,7 @@ func opcodePick(op *parsedOpcode, s *Script) error {
 		return err
 	}
 
-	if pidx.BitLen() > 32 {
-		return StackErrNumberTooBig
-	}
-
+	// PopInt promises that the int returned is 32 bit.
 	val := int(pidx.Int64())
 
 	return s.dstack.PickN(val)
@@ -1275,10 +1272,7 @@ func opcodeRoll(op *parsedOpcode, s *Script) error {
 		return err
 	}
 
-	if ridx.BitLen() > 32 {
-		return StackErrNumberTooBig
-	}
-
+	// PopInt promises that the int returned is 32 bit.
 	val := int(ridx.Int64())
 
 	return s.dstack.RollN(val)
@@ -1823,10 +1817,7 @@ func opcodeCheckMultiSig(op *parsedOpcode, s *Script) error {
 	// XXX arbitrary limits
 	// nore more than 20 pubkeyhs, or 201 operations
 
-	if numPubkeys.BitLen() > 32 {
-		return StackErrNumberTooBig
-	}
-
+	// PopInt promises that the int returned is 32 bit.
 	npk := int(numPubkeys.Int64())
 	if npk < 0 || npk > MaxPubKeysPerMultiSig {
 		return StackErrTooManyPubkeys
@@ -1848,10 +1839,8 @@ func opcodeCheckMultiSig(op *parsedOpcode, s *Script) error {
 	if err != nil {
 		return err
 	}
-	if numSignatures.BitLen() > 32 {
-		return StackErrNumberTooBig
-	}
 
+	// PopInt promises that the int returned is 32 bit.
 	nsig := int(numSignatures.Int64())
 
 	sigStrings := make([][]byte, nsig)
diff --git a/opcode_test.go b/opcode_test.go
index d5591df1..2549973c 100644
--- a/opcode_test.go
+++ b/opcode_test.go
@@ -872,12 +872,13 @@ var detailedTests = []detailedTest{
 		disassembly:    "OP_IFDUP",
 	},
 	{
-		name:        "toaltastack",
+		// alt stack is purged at the end of execution
+		name:        "toaltstack",
 		before:      [][]byte{{1}},
 		altbefore:   [][]byte{},
 		script:      []byte{btcscript.OP_TOALTSTACK},
 		after:       [][]byte{},
-		altafter:    [][]byte{{1}},
+		altafter:    [][]byte{},
 		disassembly: "OP_TOALTSTACK",
 	},
 	{
diff --git a/stack.go b/stack.go
index ffc30429..f2c96c5f 100644
--- a/stack.go
+++ b/stack.go
@@ -10,9 +10,13 @@ import (
 
 // asInt converts a byte array to a bignum by treating it as a little endian
 // number with sign bit.
-func asInt(v []byte) *big.Int {
+func asInt(v []byte) (*big.Int, error) {
+	// Only 32bit numbers allowed.
+	if len(v) > 4 {
+		return nil, StackErrNumberTooBig
+	}
 	if len(v) == 0 {
-		return big.NewInt(0)
+		return big.NewInt(0), nil
 	}
 	negative := false
 	origlen := len(v)
@@ -44,7 +48,7 @@ func asInt(v []byte) *big.Int {
 	if negative {
 		num = num.Neg(num)
 	}
-	return num
+	return num, nil
 }
 
 // fromInt provies a Big.Int in little endian format with the high bit of the
@@ -127,7 +131,7 @@ func (s *Stack) PopInt() (*big.Int, error) {
 	if err != nil {
 		return nil, err
 	}
-	return asInt(so), nil
+	return asInt(so)
 }
 
 // PopBool pops the value off the top of the stack, converts it into a bool and
@@ -155,7 +159,7 @@ func (s *Stack) PeekInt(idx int) (i *big.Int, err error) {
 	if err != nil {
 		return nil, err
 	}
-	return asInt(so), nil
+	return asInt(so)
 }
 
 // PeekBool returns the nth item on the stack as a bool without removing it.