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Any luck with winning at least NT$200 this time? A total of four uniform invoices issued in July and August had the winning serial number drawn Saturday in the bimonthly lottery draw for the top prize of NT$10 million (US$359,912).
https://focustaiwan.tw/business/202109260007
📜 [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.
👏 歡迎轉載分享鼓掌
敬 自由 / 柳根榮
信仰，是很多人的力量來源。
不同的信仰，在台灣都能給人力量。
.
來自緬甸的柳根榮阿訇(音：轟，意：教長)
在台灣宣揚伊斯蘭的教義
也見證了在台灣，各個宗教能夠相互尊重
.
外交部在今年聯合國推案影片《敬 自由》中
我們請柳根榮阿訇說出他的心聲
.
『因爲信仰而擔心、懼怕
甚至遭受各種迫害
是人類史上長存的哀痛
台灣選擇成為一個相互尊重
一起前往亮光起點的地方
穆斯林人數雖然不多
但在這裡很受到尊重』
.
如果聯合國的重要任務之一是要讓國家尊重人民的權利
台灣的夥伴價值值得聯合國重視。
.
在此感謝：
柳根榮阿訇
To Freedom / Abdullah Liu
People often draw strength from their faith and in Taiwan your access to this strength is protected, regardless of which creed you subscribe to.
Abdullah Liu is an Imam from Myanmar who spreads the teachings of Islam here and has borne witness to how the different faith groups on this island respect one another.
The Ministry of Foreign Affairs of Taiwan featured Liu in our #UNGA76 campaign video, “To Freedom,” this year, in which he shared the following reflection:
"Being worried or scared due to your faith, even undergoing all sorts of persecution, has been an ever-present sorrow in human history. Here, they decided to become a place from which to come into the light together with mutual respect. Although we Muslims are few in number, here we are truly respected."
If the UN states part of its mission as encouraging countries around the world to respect the rights of their people, Taiwan's vision of global partnership can serve as a valuable reference.
#UNGA76
#HearTaiwan
#WorkingTogether
#FreedomForAll
#UNGlobalGoals
#TaiwanCanHelp
#RespectTheRightsOfPeople
［DECKLIST］
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［music］https://youtu.be/zi1Bw9wpdNI
skill:Destiny Draw
All-Out Attacks
Lunalight White Rabbit
Lunalight Crimson Fox
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Lunalight Fusion
Kuriboh
Cosmic Cyclone
Polymerization
Predaplant Chlamydosundew
Predaplant Chimerafflesia
Labyrinth of Kline
Lunalight Purple Butterfly
Caninetaur
Number 70: Malevolent Sin
#月光牌組 你認同喜歡我的影片， 請幫我按個喜歡及訂閱頻道（鈴鐺設定記得打開）我的頻道➤https://www.youtube.com/channel/UCfFFcgSphGjLhidnrbTUlow
是我繼續製作影片的最大動力！
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I drew and counted the dots in my drawing.
It took me more than 7 days to mark 182336 and finish this drawing .
I use click software to count the number of dots.
My right hand is drawing and my left hand is clicking at the same time, to accurately count the number of dots on a drawing .
#DotsDrawing #DPARTDRAWING #182336Dots
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While only 7km tall and at its bikini line 500m wide, tiny Boracay is the Philippines' top tourist draw, fuelled by explosive growth and a tsunami of hype. The influx of visitors caused the Philippines government to temporarily close Boracay to tourists for six months. This 'rehabilitation' period, was used to restore the island to its former glory and it has since reopened with a limit on the number of daily visitors. #Shorts
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