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Self Manage is always the best ;)
Less Politic, Higher Efficiency & Lower Cost ;）
自己管理还有亲自经营还是最实际；）
少是非高效率省费用 ;)
Pengurusan diri adalah paling best ;)
Kurang Politik, Tingkatkan Prestasi Dan Kurangkan Kos ;)
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📜 [專欄新文章] Gas Efficient Card Drawing in Solidity
✍️ Ping Chen
📥 歡迎投稿： https://medium.com/taipei-ethereum-meetup #徵技術分享文 #使用心得 #教學文 #medium
Assign random numbers as the index of newly minted NFTs
Scenario
The fun of generative art NFT projects depends on randomness. The industry standard is “blind box”, where both the images’ serial number and the NFTs’ index are predetermined but will be shifted randomly when the selling period ends. (They call it “reveal”) This approach effectively solves the randomness issue. However, it also requires buyers to wait until the campaign terminates. What if buyers want to know the exact card right away? We’ll need a reliable onchain card drawing solution.
The creator of Astrogator🐊 isn’t a fan of blind boxes; instead, it thinks unpacking cards right after purchase is more interesting.
Spec
When initializing this NFT contract, the creator will determine the total supply of it. And there will be an iterable function that is randomly picking a number from the remaining pool. The number must be in range and must not collide with any existing ones.
Our top priority is accessibility/gas efficiency. Given that gas cost on Ethereum is damn high nowadays, we need an elegant algorithm to control gas expanse at an acceptable range.
Achieving robust randomness isn’t the primary goal here. We assume there’s no strong financial incentive to cheat, so the RNG isn’t specified. Implementers can bring their own source of randomness that they think is good enough.
Implementation
Overview
The implementation is pretty short and straightforward. Imagine there’s an array that contains all remaining(unsold) cards. When drawIndex() is called, it generates a (uniform) random seed to draw a card from the array, shortens the array, and returns the selected card.
Algorithm
Drawing X cards from a deck with the same X amount of cards is equal to shuffling the deck and dealing them sequentially. It’s not a surprise that our algorithm is similar to random shuffling, and the only difference is turning that classic algo into an interactive version.
A typical random shuffle looks like this: for an array with N elements, you randomly pick a number i in (0,N), swap array[0] and array[i], then choose another number i in (1,N), swap array[1] and array[i], and so on. Eventually, you’ll get a mathematically random array in O(N) time.
So, the concept of our random card dealing is the same. When a user mints a new card, the smart contract picks a number in the array as NFT index, then grabs a number from the tail to fill the vacancy, in order to keep the array continuous.
Tweak
Furthermore, as long as the space of the NFT index is known, we don’t need to declare/initialize an array(which is super gas-intensive). Instead, assume there’s such an array that the n-th element is n, we don’t actually initialize it (so it is an array only contains “0”) until the rule is broken.
For the convenience of explanation, let’s call that mapping cache. If cache[i] is empty, it should be interpreted as i instead of 0. On the other hand, when a number is chosen and used, we’ll need to fill it up with another unused number. An intuitive method is to pick a number from the end of the array, since the length of the array is going to decrease by 1.
By doing so, the gas cost in the worst-case scenario is bound to be constant.
Performance and limitation
Comparing with the normal ascending index NFT minting, our random NFT implementation requires two extra SSTORE and one extra SLOAD, which cost 12600 ~ 27600 (5000+20000+2600) excess gas per token minted.
Theoretically, any instantly generated onchain random number is vulnerable. We can restrict contract interaction to mitigate risk. The mitigation is far from perfect, but it is the tradeoff that we have to accept.
ping.eth
Gas Efficient Card Drawing in Solidity was originally published in Taipei Ethereum Meetup on Medium, where people are continuing the conversation by highlighting and responding to this story.
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The Real Threat to the US is the loss of self-confidence
──An Open Letter to Mr. Secretary Mike Pompeo
My name is Wang Ping-Chung, the spokesperson for the New Party, Taiwan’s political party. During the ongoing pandemic of the Covid-19, the enemy of all human beings, including the American people and Chinese people, is definitely the corona virus. However, as Secretary of State of the United States, you seem to consider China instead of the virus to be your enemy. It lets you do little in pandemic prevention but much in blaming the WHO and China. You have even made great efforts to politicalize the issue of public health in order to attack China, which reflects the United States’ prevailing concept of so-called China’s threat. Nevertheless, the real threat to the US is not China but the loss of self-confidence indeed.
As President Franklin Roosevelt once said, “Only thing we have to fear is the fear itself.” The threat you have to fear today is not other peoples but yourselves. Even though you have done your best to shift blames on the WHO and China, the fact is already clear of the US domestic misdiagnosed cases, which had been seen as H1N1 but in fact corona virus since last autumn. It is also your fault in underestimating the severity of the epidemic while China sacrificed itself to let the world have more preparation time. Accordingly, the Covid-19 has killed more than fifty thousand people in America. As China’s population is four times larger than the US, it is quite shocking that America’s death toll due to the Covid-19 has been above China’s.
I feel so sorry for the suffering of your people, yet it is never too late to mend. However, not only did you palm off the responsibility on others, but you also undermined international solidarity against the pandemic. Moreover, you even try to deny the status of the WHO as the coordinator for universal combat against diseases, which in some way means challenging the global institutions under the governance of the United Nations. It is so unbelievable that the United States, viewing itself as the world leader above half a century, is tending to destroy the world order recognized by the international society. The very reason I can think of is the loss of America’s self-confidence. It is the threat to both the US and the whole world.
For Liberalists in the United States, China has been believed either an opponent or a violator to international institutions. As far as it’s concerned, there had been debates whether to keep containing China economically and militarily or engaging it institutionally. Both were resulted from America’s confidence in its leadership. Consequently, the confidence gradually changed into arrogance, luring the United States into aggressions upon other countries as the global superpower without permission from the UN Security Council. It made America exhausted at last. Therefore, the United States has become an isolationist, and even a betrayer to the global institutions they established before. On the contrary, China seems more like a protector of the world order.
On the other hand, for Realists, the predominant thinkers in international politics, China has been seen as the primary rival to America. As they estimate there will be threat if any other regional hegemony occurs, the nation’s fear becomes beyond what its capability can hold. To some extent, this is the real crisis to your people. In fact, different from western nations developing themselves by oppressing and exploiting others, the Chinese people have risen out of poverty at the cost of blood, sweat, and tears of our own. I would like to remind you of Franklin Roosevelt’s self-evident words that nothing to fear but fear itself. The only threat you should conquer is the threat in your mind.
As Henry Kissinger has argued, relations between China and the United States need not – and should not – become a zero-sum game. He also suggested that China and America build a Pacific community with each other. Thinking in the same way, Chinese President Xi also claimed that the vast Pacific Ocean has enough space for the two large countries of China and the United States. Furthermore, I believe the world is large enough to embrace different political and social systems. As western liberalism in recent years has met difficulties in over-consumption and government failure, we should be more open-minded to the superiority of Chinese governance in some fields, especially the high efficiency in defeating the epidemic. The United States should also be more self-confident to have China rising under the global governance of international institutions, sharing with mutual benefits instead of destroying each other. Without doubt, only by doing so can the United States overcome the real threat and bring the world peace and prosperity, the real universal values for all mankind.
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