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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.

👏 歡迎轉載分享鼓掌

多年前看這套劇 The Expanse，看來第一季的兩集後，覺得有點悶，就開始不了了之。

近年來一直有聽到不斷有人稱讚這套科幻劇，所以最近又在看回。發現原來已經有了五季。

這不簡單啊。

所以決定又再從頭看起。

第一季要起碼要幾集後，開始看到他們對一些細節的用心。例如，在低地心吸力的行星衛星上，你倒酒是不能在酒杯上方倒，而是要用一個斜斜的角度倒酒。他們捉到了低地心吸力地帶來的人類恐怖份子，就把他掛起來站著，忍受地球地心吸力的折磨。

第一季的後半部才開始越看越有動力，我的老婆是後半段才加入的，她也看得上癮。

其中一集他們要在太空打仗，他們是沒有用防護罩，而是全部人在飛船內都要穿上太空衣，然後把船內空氣抽掉。我剛開始也不明白，然後就有驚喜了 —— 因為槍彈射過來的時候，射穿船腔，你不需要擔心氧氣漏掉而窒息。

這種細節真的是讓人嘆為觀止！

這套劇是講述未來世界，人類已經殖民了火星，和太陽系較偏遠的一些行星上的衛星和 Astroid Belt那帶的隕石。這三股勢力也開始了冷戰。當中的一些政治手腕與政治博弈非常他媽的精彩！

怎麼精彩法？

第一季的爛番茄分數是 75%。

第二季是95%。

之後的三季，每一季都 100%！！

我第二季才看到一半，但真他媽的比第一季強。

我現在回想為何我幾年前沒有看完，我發現有兩個理由：

一，開始那兩三集，節奏有一點慢。

二，我不喜歡第一季裡面的那個警察角色（也是主角之一）。

這套劇最大吸引力的地方，除了是那星際的政治角力，當中有不少地方，他們不用透過講話來惹人深思，而是透過劇情和角色做的抉擇來帶出。例如：政治骯髒的必要性、科學與道德的衡量、有很大理想的人會怎樣殘害到身邊的人。

江魔高度推薦！！

如果你喜歡 Nolan 的 Batman三部曲那種讓人深思道德的課題，這套美劇絕對不會差過它。

09.23 20:00 上架（連結上架後更新）

——

... and you look out at this great big blue expanse, and it's shimmering and it's moving and there's waves and there's surf and there's tides, but you have no idea for what lies in there. The problem, I think, is that we take the ocean for granted.

當你看著大海一望無際的藍，如此波光粼粼、驚濤駭浪，它有風浪、有狂瀾、也有高低潮汐，但我們對底下的世界一無所知，真正的問題，也許是對於海洋的存在，太過理所當然。

——

2022 年，我希望每天能借用你一分鐘的時間，和你介紹一種海洋生物。

有在沸水中生活的蠕蟲、在零下水域安居的冰魚；
有可以返老還童的水母、可以男扮女裝的烏賊
有會畫畫的河豚、會跳舞的蝦子、會唱歌的鯨魚

而日曆的名字，叫做《漫遊者號》，源自 MBARI 深海探測器的名字。我期待他能像一台小潛水艇，帶大家一窺海中的世界。

＊Facebook: https://www.facebook.com/oceanroverslog
＊Instagram: https://www.instagram.com/oceanroverslog/
＊Email: oceanroverslog@gmail.com

JJ Lin 林俊傑 《倖存者· 如你》維度二 首張全英文EP《Like You Do》
OUT NOW 全面數位發行 https://jjlin.lnk.to/LYDAY

Have you imagined a world where
You’re more than just You?
What would that be like?

Drifter • Like You do - a Double-dimensional, deluxe EP creatively led by JJ Lin, from music productions to visual concepts. The music narrative of DRIFTER • LIKE YOU DO is inspired by a concept JJ has been ruminating on - the possibility of a parallel universe.

In this latest release which marks JJ’s 14th album, as well as his first english EP throughout his illustrious career of 18 years, JJ delves into his innermost thoughts and feelings, redefining his music perspectives to put forward a stripped down and introspective representation of his music and self.

In Quantum Theory
Space and time are not continuous
A parallel universe is a possibility
Could it be possible that somewhere, somehow
In an obscure corner of the universe
An infinite number of us exist?
Where perhaps, I could be you, and you could be me?

I seem to be a Drifter in this vast expanse... Like You Do.

-

[DRIFTER • LIKE YOU DO ]

Part One: The 1st Dimension - DRIFTER

Music has always been an expression of self for JJ. His journey of self-discovery could be traced back to his From M.E. To Myself (2015) album, with him eventually finding the connection between himself and the world, and shared through his Message in a Bottle (2017) album.

In the recent years, JJ embarked on a different route to self-discovery as he shifts the focus of his music from self to “you”. Conveyed through his double EP DRIFTER • LIKE YOU DO, JJ propounds a new direction for self-reflection.

DRIFTER EP features six brand new Mandarin songs that weaved together a complete concept of: What would you do, if you, were not just you? The songs inspire us to contemplate the possibility that our consciousness could determine who we are - there could be multiple endings to every story, and when we believe so, the future will be limitless.

Part Two: The 2nd Dimension - LIKE YOU DO

An extension of Drifter, LIKE YOU DO explores a self-examining concept: What is left after you rid yourself of expectations?

When darkness descends, have you, in pursuit of survival, stumbled upon another version of yourself that is so foreign yet familiar? You could be that drifter, that is the only glimpse of hope left in a despondent world. Which version of you would emerge in face of adversity? If a parallel universe does exist, JJ is breaking out of his shell and introducing the hidden version of himself that we have yet to meet via LIKE YOU DO.

Partnered with new music collaborators Fernando Garibay, Nasri Atweh, Joshua Kissiah Cumbee, Ramiro Padilla and Daniel Padilla, JJ endeavours to offer fresh perspectives and sounds for this EP.

The journey and story of this alternate JJ Lin has just begun.

—

“All these years, one thing I’ve learnt is that it’s one of the hardest things in life to accept the flawed version of ourselves. We work so hard to be the best and to be perfect; many times we want to believe that we are unstoppable, and that only by being strong, we can be successful.

“Like You Do” to me is the opposite of that.

Every song is a reflection of the darker version of myself. And I’ve found a sense of healing, by reaching in and realising that true strength is found in embracing every version of the self. It’s only when you strip yourself of all expectations, that your every next step will be a form of gain and reward.

There is beauty in that.”

— JJ Lin

＿＿＿

近年來我深深體悟到一件事：接受有缺憾的自我，是一生中最難的事情之一。
對於任何事務，我們努力做到最好、盡可能達到完美；很多時候，我們試著去相信自己是無懈可擊的，因為唯有堅強，才能成功。

然而，【Like You Do】對我而言正是相反的。
每首歌，都反映出自己的內心深處某個曾不可觸及的一面。過程中，通過自我剖白來學習擁抱自己的不完美，並找到真正的力量。而從中，我被療癒了。
當你擺脫所有期望時，每一步都將轉化為獲得和回報。
那正是最美的。

- JJ 林俊傑

【Like You Do】中的JJ Lin是一鍵歸零，
也是一步躍進。 跳脫既定模板，拋開過往的該與不該。

在【Like You Do】EP中，JJ Lin回到做音樂的本質面貌說故事，當這個語言更加直覺，遇見的自己就越加真實。捧著初衷的純粹，JJ成為昏暗夜晚中的一雙堅定眼神，穿透情感與歲月的虛與實。一刻明亮的獲得，是歷經所有的願與不願，坦然面對這些擁有與失去，於是回歸誠實後的純粹，如這世界上的每一個你，重新擁抱世界附加在自己身上的能量。

為帶給這張全英文EP更完整的體驗，JJ遠赴異地，尋找更多不同的聲音，當沒有任何模板框架，跳脫以往的創作模式，他的音樂更加自我也更加自由。JJ邀請多次獲得葛萊美獎項提名之專輯製作人- Fernando Garibay、Joshua Kissiah Cumbee、Ramiro Padilla、Daniel Padilla等多位專業音樂人攜手創作。與全新的音樂夥伴合作，無論曲、詞，JJ自在地享受，完全地吸收來自不同的音樂人所給予的能量，共同激盪出不同以往的音樂風格。一切不經設定、沒有設限也沒有包袱，放下習慣的唱腔，衝撞出全新的聲音。所有面貌都是最原始最嶄新，也是翻面後的第一頁。

歸零的同時，就會遇見真實的自己。

這個挑戰，是JJ 17年來從未有過的經驗，在華語市場中多年的累積，逐漸締造屬於最JJ的音樂版圖。但這一次，林俊傑顛覆一切的認知、放下一切的理所當然與成長脈絡，為了自我實現的這一刻，成為了歸零的JJ Lin，勇敢擁抱陌生的環境與不同的音樂文化，JJ已經不是JJ，但也不再只是原本的JJ。


#JJLINLikeYouDo
#JJXIV

#無人之島 #魯曼 #任然 #魯曼英文
完整歌詞英翻中
黑色的背後是黎明
In the back of darkness is dawn.
以為來日方長所以別把夢吵醒
I think we still have a lot of time in the future, so don’t interrupt the dreaming.
時間它繼續飛行
Time keeps flying.
下一站機場門外 擁抱你的背影
Next stop I will hug the sight of your back outside the airport gate.
藍色的背後是純淨
In the back of blue is pureness.
低下頭俯瞰陸地上想念的眼睛
I look down at the ground with yearning eyes.
生命中有些事情
In our lives, there are some situation
從沒有原因說明 一剎那的寂靜
in which we can’t find the reason for the transient silence.
如果雲層是天空的一封信
If a cloud is a letter in the sky.
能不能再聽一聽 聽你的聲音
Can I once again hear your voice?
就算是探秘 (是貪玩而已)
Let’s just call it an exploration,
跟著潘彼得去無人島旅行
following Peter Pan to take a trip in a deserted island.

我不會怪你的
I won’t blame you.
天空一望無際 是海洋的倒影
The boundless expanse of the sky is the reflection of the ocean.
藍色一望無際 我的你在哪裡
In boundless expanse of blue, where are you, who belongs to me
假如迷路了一定 （記得）把思念裝進漂流瓶
If you are lost, remember to put your yearning into the drifting bottle,
(記得)快寄給我別讓人擔心
sending it to me soon, and leaving me with no worry.
藍色的背後是純淨 （雲淡風輕）
In the back of blue is pureness.
低下頭俯瞰陸地上想念的眼睛
I look down at the ground with yearning eyes.
生命中有些事情 （不能透明）
In our lives, there are some situation

從沒有原因說明 一剎那的寂靜
in which we can’t find the reason for the transient silence.
如果雲層是天空的一封信
If a cloud is a letter in the sky.
能不能再聽一聽 聽你的聲音
Can I once again hear your voice?
就算是探秘(是貪玩而已)
Let’s just call it an exploration,
跟著潘彼得去無人島旅行
following Peter Pan to take a trip in a deserted island.
我不會怪你的
I won’t blame you.
天空一望無際 是海洋的倒影
The boundless expanse of the sky is the reflection of the sky.
藍色一望無際 我的你在哪裡
In the boundless expanse of blue, where are you, who belongs to me?
假如迷路了一定 （記得）把思念裝進漂流瓶
If you are lost, remember to put your yearning into the drifting bottle,
(記得)快寄給我別讓人擔心
sending it to me soon, and leaving me with no worries.
如果雲層是天空的一封信
If a cloud is a letter in the sky,
能不能再聽一聽 聽你的聲音
can I once again hear your voice?
就算是探秘
Let’s just call it an exploration,
跟著潘彼得去無人島旅行
following Peter Pan to take a trip in the deserted island.
我不會怪你的
I won’t blame you.
天空一望無際 是海洋的倒影
The boundless expanse of the sky is the reflection of the ocean.
藍色一望無際 我的你在哪裡
In the boundless expanse of blue, where are you, who belongs to me?
假如迷路了一定 （記得）把思念裝進漂流瓶
If you are lost, remember to put your yearning into a drifting bottle,
(記得)快寄給我別讓人擔心
sending it to me soon, and leaving me with no worries.