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+# 抽象真可能引入负成本
+
+> :fontawesome-regular-face-grin: 洋葱
+>
+> :material-clock-edit-outline: 2023年7月27日 21:23:44
+
+抽象一般增加无用功能，降低性能。然而另一方面，更清晰的结构也给了编译器更多自由去优化。
+
+下面两个 rust 函数功能完全相同，只是第二个`opt1_idiomatic`采用了更抽象的函数式写法。实测`opt1_idiomatic`的性能是`baseline`是几到十几倍。
+
+```rust
+fn baseline(input: &str) -> i64 {
+    let mut res = 0;
+    for b in input.bytes() {
+        match b {
+            b's' => res += 1,
+            b'p' => res -= 1,
+            _ => continue,
+        }
+    }
+    res
+}
+```
+
+```rust
+fn opt1_idiomatic(input: &str) -> i64 {
+    input
+        .bytes()
+        .map(|b| match b {
+            b's' => 1,
+            b'p' => -1,
+            _ => 0,
+        })
+        .sum()
+}
+```
+
+:material-eye-arrow-right-outline: [{n} times faster than C, where n = 128 - Thomas Ip](https://ipthomas.com/blog/2023/07/n-times-faster-than-c-where-n-128/)
+
+:material-eye-arrow-right-outline: [tommyip/n\_times\_faster\_than\_c: Code for blog post "{n} times faster than C, where n = 128"](https://github.com/tommyip/n_times_faster_than_c)
+
+作者使用 Apple M1 Pro。如果你不是 ARM 架构，测试前需要删除平台相关的函数。