From: "Zack Weinberg" <zack@owlfolio.org>
To: "GNU libc development" <libc-alpha@sourceware.org>
Subject: Re: bug fix for hp-timing.h (aarch64)
Date: Wed, 11 Jan 2023 12:22:11 -0500 [thread overview]
Message-ID: <3dd92ee4-00b4-4bf2-ae8c-908a29752198@app.fastmail.com> (raw)
In-Reply-To: <8ae95272accb441aad774a5f10d27d57@amazon.com>
On Wed, Jan 11, 2023, at 11:44 AM, Tang, Jun wrote:
> On Graviton 3 the frequency is 1050000000 and the original function
> hp-timing.h no longer gives the correct answer. The following patch can
> fix the bug:
Please try this instead:
> - (Diff) = ((End) - (Start)) * (UINT64_C(1000000000) / freq); \
> + (Diff) = (((End) - (Start)) * UINT64_C(1000000000)) / freq; \
This avoids using floating-point arithmetic but should still do the rescale correctly.
(The multiplier and divisor are both guaranteed to be less than 2**32, so, as long as we do the multiplication in 64-bit arithmetic, we cannot lose bits via overflow.)
zw
next prev parent reply other threads:[~2023-01-11 17:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-11 16:44 Tang, Jun
2023-01-11 17:22 ` Zack Weinberg [this message]
2023-01-31 14:47 ` Tang, Jun
2023-01-11 22:49 Wilco Dijkstra
2023-01-12 14:38 ` Tang, Jun
2023-01-12 18:07 ` Wilco Dijkstra
2023-01-12 18:54 ` Zack Weinberg
2023-01-12 20:32 ` Wilco Dijkstra
2023-01-12 20:51 ` Noah Goldstein
2023-01-16 16:33 ` Wilco Dijkstra
2023-01-16 17:01 ` Noah Goldstein
2023-01-16 18:35 ` Wilco Dijkstra
2023-01-12 15:11 ` Zack Weinberg
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