From 9a4920d565e5b241c9c9bdf0b2edda81cf749d2b Mon Sep 17 00:00:00 2001
From: yjwxfq <112159687+yjwxfq@users.noreply.github.com>
Date: Thu, 8 Jun 2023 15:36:41 +0800
Subject: [PATCH] Update token_contract.go, modify the overflow judgment
 condition for function sub().

The general overflow judgment condition for function sub is not in every case.
The judgment result is wrong in the condition of b < 0 && q >=0
for example, b = -3, q = 2, diff = -5, it's not overflow,
but if (diff > b) == (b >= 0 && q >= 0) wil be true.

for another example, b = -3, q = maxint, b-q is overflow,
but if (diff > b) == (b >= 0 && q >= 0) wil be false.

Signed-off-by: yjwxfq <112159687+yjwxfq@users.noreply.github.com>
---
 token-erc-20/chaincode-go/chaincode/token_contract.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/token-erc-20/chaincode-go/chaincode/token_contract.go b/token-erc-20/chaincode-go/chaincode/token_contract.go
index b6b7bad6..9752fd3c 100644
--- a/token-erc-20/chaincode-go/chaincode/token_contract.go
+++ b/token-erc-20/chaincode-go/chaincode/token_contract.go
@@ -723,7 +723,7 @@ func sub(b int, q int) (int, error) {
 	var diff int
 	diff = b - q
 
-	if (diff > b) == (b >= 0 && q >= 0) {
+	if (diff < b || diff < -q) == (b >= 0 && q <= 0) {
 		return 0, fmt.Errorf("Math: Subtraction overflow occurred  %d - %d", b, q)
 	}