IT討論區(80) 做連卡佛真係好幸福,有得減薪50%,IT狗就已被炒,減薪100%
ミクミク９９
1001 回覆
8 Like
0 Dislike
第 1 頁第 2 頁第 3 頁第 4 頁第 5 頁第 6 頁第 7 頁第 8 頁第 9 頁第 10 頁第 11 頁第 12 頁第 13 頁第 14 頁第 15 頁第 16 頁第 17 頁第 18 頁第 19 頁第 20 頁第 21 頁第 22 頁第 23 頁第 24 頁第 25 頁第 26 頁第 27 頁第 28 頁第 29 頁第 30 頁第 31 頁第 32 頁第 33 頁第 34 頁第 35 頁第 36 頁第 37 頁第 38 頁第 39 頁第 40 頁第 41 頁
大聲啲講多次 返工為左咩
TL;DR you should not treat C as portable assembly anymore.
C is no longer portable assembly because compilers are so smart today. C compilers can generate code that looks very different from what programmers expect as long as the semantics is the same according to language specifications. A few examples:
1. Optimizing compilers do loop transformation. A simple for loop can be unrolled and peeled.
2. With SIMD instructions available on all major CPUs, most compilers do vectorization. A Loop can be transformed into equivalent using vector instructions. With 1), a simple C loops in a few lines can be compiled into many hundreds of instructions because the compiler aggressively unrolls and vectorizes the loop.
3. Compilers recognize some common code patterns can replace those with calls to run-time library functions. If you write a loop to copy memory, the compiler may replace that with a call to memcpy(). Question: what if I am implementing my own memcpy() in C?
4. Compilers take advantage of undefined behaviours in language specifications. It can do anything, including deleting your code in your back if you write code with undefined behaviours. For example, you should not check integer overflow in C using "if (x + 1 < x) { /* overflow */}". Your compiler can delete the whole thing without notice.
C is no longer portable assembly because compilers are so smart today. C compilers can generate code that looks very different from what programmers expect as long as the semantics is the same according to language specifications. A few examples:
1. Optimizing compilers do loop transformation. A simple for loop can be unrolled and peeled.
2. With SIMD instructions available on all major CPUs, most compilers do vectorization. A Loop can be transformed into equivalent using vector instructions. With 1), a simple C loops in a few lines can be compiled into many hundreds of instructions because the compiler aggressively unrolls and vectorizes the loop.
3. Compilers recognize some common code patterns can replace those with calls to run-time library functions. If you write a loop to copy memory, the compiler may replace that with a call to memcpy(). Question: what if I am implementing my own memcpy() in C?
4. Compilers take advantage of undefined behaviours in language specifications. It can do anything, including deleting your code in your back if you write code with undefined behaviours. For example, you should not check integer overflow in C using "if (x + 1 < x) { /* overflow */}". Your compiler can delete the whole thing without notice.
You can turn off all optimizations with a command line flag like -O0 or turn off individual optimization.
You don't want to turn off optimizations normally as you are going to drop tonnes of performance if you do so. I do low-level system programming for a living and I write assembly very rarely. If I do, I prefer embedding code inside C/C++ code instead of writing in pure assembly.
You don't want to turn off optimizations normally as you are going to drop tonnes of performance if you do so. I do low-level system programming for a living and I write assembly very rarely. If I do, I prefer embedding code inside C/C++ code instead of writing in pure assembly.
C Is Not a Low-level Language
Your computer is not a fast PDP-11.
David Chisnall
In the wake of the recent Meltdown and Spectre vulnerabilities, it's worth spending some time looking at root causes. Both of these vulnerabilities involved processors speculatively executing instructions past some kind of access check and allowing the attacker to observe the results via a side channel. The features that led to these vulnerabilities, along with several others, were added to let C programmers continue to believe they were programming in a low-level language, when this hasn't been the case for decades.
...
https://queue.acm.org/detail.cfm?id=3212479
Your computer is not a fast PDP-11.
David Chisnall
In the wake of the recent Meltdown and Spectre vulnerabilities, it's worth spending some time looking at root causes. Both of these vulnerabilities involved processors speculatively executing instructions past some kind of access check and allowing the attacker to observe the results via a side channel. The features that led to these vulnerabilities, along with several others, were added to let C programmers continue to believe they were programming in a low-level language, when this hasn't been the case for decades.
...
https://queue.acm.org/detail.cfm?id=3212479
LinkedIn 有啲 agent真係好垃圾
野雞大學讀marketing
然後做左agent 3個月唔夠就話幫你揾工同改善你interview技巧
fountend backend都未分到
呀叔我見工多過你過靚妺in人啦
毛都未出整
想in我?去時鐘酒店咪慢慢同你in
野雞大學讀marketing
然後做左agent 3個月唔夠就話幫你揾工同改善你interview技巧
fountend backend都未分到
呀叔我見工多過你過靚妺in人啦
毛都未出整
想in我?去時鐘酒店咪慢慢同你in
有d 仲搞笑，fg agent 做得幾個多去話教我呢d experienced professional 點plan career 同比意見我。
唔學low level就要學design pattern先高人工
乜都唔識
好想fg妹妹幫我plan career
2） 我好想知其實database既operation有冇用simd?我睇postgresql d source code都係for loop
Github 有一個800 Stars 130fork既vue project, 但人地好似睇唔上眼咁
咁你不如花D時間睇下果800個比stat你既人，有冇請緊人