📜 [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

永真在這邊跟您報告一下 #週三晚上IG直播見 🔥💫⚡
　
還記得 VOGUE Taiwan 初夏推出的特別版封面嗎？經過數月籌劃、總部細節確認以及農民曆選日子，VOGUE Taiwan 的首張 2D 動態 NFT，即將登場 。

VOGUE Taiwan’s first historic NFT depicting a scene of hope amidst the pandemic.
　
9/22 (三) 21:00-22:00 ｜ NFT 跨界對談 IG 直播
　
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對談陣容

－前瞻科技傳教士 ｜ 葛如鈞（寶博士）#主持
－《VOGUE》亞太區編輯總監 ｜ 孫怡 Leslie Sun
－知名平面設計師 ｜ 聶永真 Aaron Nieh（我🙋🏻‍♂️）
－秘銀、Cream Financet 創辦人 ｜ 黃立成 Jeffrey Huang
————————————————————
　
NFT，藝術創作在數位化時代下的趨勢；
歡迎鎖定我們的 IG 帳號，星期三晚上九點線上見：

VOGUE Taiwan —— voguetaiwan
孫怡 —— sunles
聶永真 —— aaronnnieh
黃立成 —— machibigbrother
　
　
#NFT #VOGUETAIWAN #VogueCover #寶博士 #孫怡 #聶永真 #黃立成 #LeslieSun #AaronNieh #JeffreyHuang

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VOGUE Taiwan’s first historic NFT depicting a scene of hope amidst the pandemic

Since the cover received attention from many after its release, and since nothing is philosophically and aesthetically impossible to rethink in the era in which every moment is uploaded on the Internet, the plan of minting this cover as an NFT was also initiated later in July. After intense discussion with VOGUE Taiwan and process tuning with VOGUE’s international headquarters, the NFT was lately minted and will be officially listed in late September.

Owing to its digital characteristics, the NFT will be presented in subtle 2D animation, creating a distinction from the still image on the paper cover.

Please stay tuned and welcome to our IG live at 21:00 Taiwan Time on 22 September.

近年掀起NFTs 熱潮，從藝術品到球員卡到運動比賽的精華片段，不少人開始投資一種名為NFTs (Non-fungible Tokens）的數位資產。有人説如果ANDY WARHOL 是這個年代的人，他應該也會是NFT界的活躍份子。科技日新月異，真的要每天多多學習，好好吸收😊
NFTs are one-of-a-kind digital collectibles and their products range from digital paintings and artworks to the latest Kings of Leon album and sports merchandise.
Some even suggested that if Andy Warhol had been born in the 90s, he probably would have minted Campbell's Soup as a NFT.
You learn something new every day 😊

#NFT #NFTs #非同質化代幣 #區塊鏈 #Drmarcus #郭醫生 #知識 #knowledge #投資 #investment

【EddieCooking】香煎嫩滑三文魚配青豆薄荷醬及風琴焗薯 Pan Fried Salmon & Hasselback Potato

材料 Ingredients

一人份量 One serving

香煎嫩滑三文魚配青豆薄荷醬 Pan Fried Salmon on Minted Peas
三文魚排 300g Salmon fillet
青豆 200g Green peas
新鮮薄荷葉 Fresh mint leaves
無鹽牛油 45g Unsalted butter
芥花籽油 Canola Oil
鹽 Salt

檸檬酸豆牛油 Lemon Caper butter
酸豆 3 茶匙 3 tablespoon Capers
無鹽牛油 25g Unsalted butter
檸檬 1/2 Lemon
鹽 Salt

風琴焗薯 Hasselback Potato
薯仔 1 Potato
百里香 Thyme
橄欖油 Olive Oil
鹽 Salt


風琴焗薯 Hasselback Potato
1. 焗爐預熱185度。
Preheat over to 185c.
2. 將薯仔切成風琴狀，每層約2mm厚。底部預留1.5cm，不要切斷。
Slice the potato the same way as the video, about 2mm between each cut. Do not cut to the bottom, about 1.5cm from the bottom usually works well.
3. 薯仔放置焗盆上，淋上適量橄欖油。加份鹽調味後，放入焗爐。
Place the potato on a baking tray, drizzle a good amount of olive oil on the potato. Sprinkle some salt and place in oven.
4. 185度焗60分鐘至金黃色。
Bake 60mins until the potato is crispy on the edges.
5. 焗好後放上新鮮百里香。
Add some fresh thyme to the potato before eating.


青豆薄荷醬 Minted Peas Sauce
1. 青豆加入講量鹽煮熟後，瀝乾及放入攪拌機。
Boil some frozen peas in salted water. Remove from water and put into a blender.
2. 加入薄荷葉、牛油及適量鹽。攪拌至蓉狀。
Add mint leaves, butter and salt, blend.


檸檬酸豆牛油 Lemon Caper butter
1. 加熱平底鑊。檸檬切半後，放至熱鑊上，煎至表面呈焦糖色。
Cut half a lemon and place it on a hot pan until it is slightly caramelized.
2. 牛油放入另一平底鍋內。
Add butter into a saucepan.
3. 酸豆搾乾水份，加入平底鍋內。煮一分鐘後放置。
Squeeze the water from the capers and add into butter, set aside after about 1min of cooking.


香煎嫩滑三文魚 Pan Fried Salmon
1. 三文魚排清洗乾淨及抹乾，放置室溫。
Clean and dry the piece of salmon fillet and make sure it is at room temperature before you start cooking it.
2. 熱平底鑊加入芥花籽油。
Heat pan and add Canola oil.
3. 芥花籽油加熱後，放入三文魚排，魚皮一面朝下。
When the oil is very hot, place salmon skin side down.
4. 灑上鹽調味。
You can salt the salmon now.
5. 煎約2分鐘後反面。
Flip over after about 2mins.
6. 魚皮面灑上適量鹽調味。將熱油淋上魚皮面，繼續煎香。
Salt the skin side and spoon hot oil over the fish and keep cooking.
7. 煎約3分鐘後，盛起三文魚排，放置。
Total cooking time is usually around 5mins. Set fish aside once done.
8. 將三文魚放於青豆醬上。淋上酸豆牛油及擠檸檬汁。
Add minted peas to plate, place salmon fillet on top, spoon on the capers and butter mixture. Add a squeeze of the lemon.


Notes from Eddie:

1. Make sure the salmon fillet is in room temperature before you start cooking. I would bring out the fish about an hour before I start cooking.
2. Make sure the fillet is quite dry before you cook. Use a knife to scrape off any excess moisture from the skin.
3. You can use fresh peas if you can find, but frozen one is also fine.
4. Use Canola oil for panfrying salmon fillet. It is better for the recipe as the oil has a higher burning point.
5. While frying the fish, I usually lift the fish to check the skin, you want it to turn golden brown.

關於此食譜 About:
This is one of my favourite ways to eat Salmon. I also like it because it’s quite simple to make. Try your best to buy some good quality salmon, my favourite is King Salmon from New Zealand. My favourite part of the salmon is the belly so make sure you get a piece that includes some belly parts. The most important part of this salmon is making sure that its quite dry before you cook. There is a lot of moisture in the skin and I find the best way is to scrape it off with a knife. Keep scraping till no more moisture comes off the skin of the fish. Dry the other side with some kitchen towel. I prefer not to salt the fish until I cook it as more moisture will come off the fish if you salt it too early.


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(This interview was recorded in November 2020.)

In 2019, according to the Pentagon, China launched more ballistic missiles for testing and training than the rest of the world combined. It did it through its newly minted rocket force, the People's Liberation Army Rocket Force - acronym P-L-A-R-F.

PLARF is a critical component of China's nuclear deterrence strategy to deter and counter third-party intervention in regional conflicts. China's current defense minister, General Wei Fenghe, knows missiles. He was previously the commander of the predecessor of PLARF before PLARF was reorganized and given its new name.

Mark Stokes is our guest today. He is executive director of the Project 2049 Institute, a think tank based in Washington, DC. Mr. Stokes is a 20-year United States Air Force veteran who served in intelligence planning and policy roles.


Today’s episode is hosted by J.R. Wu - Chief of the Secretariat for INDSR (Institute for National Defense and Security Research) in Taiwan. Wu is a former journalist with nearly two decades of media experience in the US and Asia. She has led news bureaus for Reuters and Dow Jones.


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