add int overflow check for 32-bit systems (#553)

Author: phillip-stephens

src/internal/cachehash/shardedcachehash.go

@@ -35,7 +35,13 @@ func (c *ShardedCacheHash) Init(maxLen int, shards int) {
 
 func (c *ShardedCacheHash) getShardID(k interface{}) int {
 	kb := []byte(fmt.Sprintf("%v", k))
-	return int(crc32.ChecksumIEEE(kb)) % c.shardsLen
+	hash := int(crc32.ChecksumIEEE(kb))
+	// crc32 returns a 32-bit unsigned integer. On 32-bit systems, this int cast can return negative values.
+	// To ensure we always have 0 <= shard ID < shardsLen, we take the absolute value of the hash.
+	if hash < 0 {
+		hash = -hash
+	}
+	return hash % c.shardsLen
 }
 
 func (c *ShardedCacheHash) getShard(k interface{}) *CacheHash {