Understand your Mac and iPhone more deeply by tracing the evolution of Mac OS X from prelease to Swift. John Siracusa delivers the details.
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;; based on core.logic 0.8-alpha2 or core.logic master branch | |
(ns sudoku | |
(:refer-clojure :exclude [==]) | |
(:use clojure.core.logic)) | |
(defn get-square [rows x y] | |
(for [x (range x (+ x 3)) | |
y (range y (+ y 3))] | |
(get-in rows [x y]))) |
/** | |
* Fancy ID generator that creates 20-character string identifiers with the following properties: | |
* | |
* 1. They're based on timestamp so that they sort *after* any existing ids. | |
* 2. They contain 72-bits of random data after the timestamp so that IDs won't collide with other clients' IDs. | |
* 3. They sort *lexicographically* (so the timestamp is converted to characters that will sort properly). | |
* 4. They're monotonically increasing. Even if you generate more than one in the same timestamp, the | |
* latter ones will sort after the former ones. We do this by using the previous random bits | |
* but "incrementing" them by 1 (only in the case of a timestamp collision). | |
*/ |
Latency Comparison Numbers (~2012) | |
---------------------------------- | |
L1 cache reference 0.5 ns | |
Branch mispredict 5 ns | |
L2 cache reference 7 ns 14x L1 cache | |
Mutex lock/unlock 25 ns | |
Main memory reference 100 ns 20x L2 cache, 200x L1 cache | |
Compress 1K bytes with Zippy 3,000 ns 3 us | |
Send 1K bytes over 1 Gbps network 10,000 ns 10 us | |
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD |