It's not clear if hardware or software is to blame.

Buyers in Taiwan who had pre-ordered Apple's new #iPhone13 models rushed to pick up their orders Friday, with some people lining up for hours outside the stores.
https://focustaiwan.tw/business/202109240006

📜 [專欄新文章] Gas Efficient Card Drawing in Solidity

✍️ Ping Chen

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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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ชมสายการผลิต All-New Hyundai Santa Cruz 2022 ฮุนได ซานตาครูซ รถกระบะปิกอัพขนาดเล็ก โครงสร้างแบบ Unibody (Monocoque)

Hyundai Motor Manufacturing Alabama Celebrates Launch of All-New 2022 Santa Cruz
Montgomery, Ala. June 22, 2021 – Hyundai Motor Manufacturing Alabama (HMMA) celebrated the launch of the all-new 2022 Santa Cruz Sport Adventure Vehicle on Tuesday, June 22, 2021. The Santa Cruz joins the Sonata and Elantra sedans and Santa Fe and Tucson SUVs on the Montgomery assembly line. This addition marks the first time HMMA has produced five vehicles at once.

The highly-anticipated Santa Cruz Sport Adventure Vehicle shatters both SUV and truck segments, creating an entirely new vehicle category. The Santa Cruz features a secure, open bed area which includes a lockable tonneau cover and hidden bed storage for diverse gear-carrying flexibility.

“Santa Cruz, with its bold styling, breaks open an all new segment territory, both for Hyundai and the industry as a whole. Open-bed flexibility coupled with closed-cabin security meets the changing everyday needs of its adventure-oriented buyers, while powerful and efficient engines and superb maneuverability ensure it is a pleasure to drive in urban or off-road environments. Our customers will wonder just how they managed before owning one,” said Jose Munoz, president and CEO, Hyundai Motor North America.

HMMA recently completed a plant expansion project to support adding the Santa Cruz to HMMA’s product mix. The addition of the Santa Cruz will further enhance HMMA’s ability to adjust its vehicle production with market demand and stay competitive in the ever-changing automotive market.

“We are excited and honored to be producing Hyundai’s first open bed vehicle for the North American market,” said HMMA President and CEO, Ernie Kim. “The launch of the Santa Cruz is a further testament to the trust Hyundai Motor company puts in HMMA and our Alabama home. I am so proud of our Team Members for accomplishing this achievement while the world is going through such difficult times. We can’t wait for our customers to experience the innovative design and world class quality the Santa Cruz will bring to the table.”

The addition of the Santa Cruz will continue to sustain high-quality jobs at HMMA and throughout its supplier base.

The 2022 Hyundai Santa Cruz will begin arriving in U.S. dealerships later this summer.

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