Top all-time · #7680
Krister Walfridsson
Personal blog · kristerw.github.ioprogrammingsystems
Krister Walfridsson's personal blog at kristerw.github.io covers programming and systems. Since 2021, 10 different Hacker News readers have linked it 19 times, most often “Verifying GCC optimizations using an SMT solver”. It is still writing: the last post was on 2026-04-10, and you can follow it by feed.
Too few sampled comments (3) to say how often HN recommends it.?
Why HN links it
Linked for explanations of floating-point behaviour, fast-math and FMA contraction in compilers. One commenter calls it a post that gets the same information across with fewer words than another post on the topic.
Summarised by Claude from a sample of 3 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Compilers, programming languages, etc.
Most-linked posts?
- Verifying GCC optimizations using an SMT solver3 people · 3 mentions · first linked 2022-11-02
- -ffp-Contract=Fast3 people · 3 mentions · first linked 2021-11-09
- Optimizations Enabled by -ffast-Math3 people · 3 mentions · first linked 2021-10-19
- Branch/Cmove and Compiler Optimizations2 people · 2 mentions · first linked 2022-05-24
- GCC Translation Validation2 people · 2 mentions · first linked 2022-09-14
What Hacker News says?
2001 - GCC 3.0: - Introduction of `-ffast-math`: The `-ffast-math` flag was introduced, enabling aggressive floating-point optimizations at the cost of strict IEEE compliance. 2004 - GCC 3.4: - Refinements and Extensions: Additional optimizations added, including better handling of subnormal numbers and more aggressive operation reordering. 2007 - GCC 4.2: - Introduction of Related Flags: `-funsafe-math-optimization…
Comment linking /
on “Someone's been messing with Python's floating point subnormals”Submitted Optimizations Enabled by -ffast-Math as a story · 209 points
HN discussionThe actual rules are very complicated. C allows greater precision for intermediate results but compilers are sometimes careful to stick to IEEE rounding. [1] contains a good general overview, and [2] talks about FMA in particular. And in [3] I've set up a Godbolt example to play with. By default -O3 gives you FMA, but -O or -O3 with -ffp-contract=off don't. So you absolutely can get different results depending on op…
Comment linking /2021/11/09/fp-contract/
on “Race Conditions Can Be Useful for Parallelism”Submitted Verifying GCC optimizations using an SMT solver as a story · 121 points
HN discussionRecent post on the same topic that gets the same information across with fewer words: https://kristerw.github.io/2021/10/19/fast-math/
Comment linking /2021/10/19/fast-math/
on “Understanding Fast-Math”Submitted Branch/Cmove and Compiler Optimizations as a story · 83 points
HN discussionSubmitted Writing a GCC Plugin in Python as a story · 3 points
HN discussionSubmitted Strange behavior with NaN and -ffast-math as a story · 3 points
HN discussionSubmitted -ffp-Contract=Fast as a story · 2 points
HN discussionSubmitted Verifying GCC optimizations using an SMT solver as a story · 2 points
HN discussionSubmitted GCC Translation Validation 2: Verifying GCC optimizations using an SMT solver as a story · 2 points
HN discussionSubmitted Writing a GCC Plugin in Python as a story · 2 points
HN discussionSubmitted Branch/Cmove and Compiler Optimizations as a story · 2 points
HN discussionSubmitted -ffp-Contract=Fast as a story · 2 points
HN discussionSubmitted GCC Translation Validation Part 6: Uninitialized Memory as a story · 1 points
HN discussionSubmitted GCC Translation Validation Part 4: Address Calculations as a story · 1 points
HN discussionSubmitted GCC Translation Validation as a story · 1 points
HN discussionSubmitted GCC Translation Validation as a story · 1 points
HN discussionSubmitted Optimizations Enabled by -ffast-Math as a story · 1 points
HN discussion
