From: Bruce Richardson <bruce.richardson@intel.com>
To: Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: "Morten Brørup" <mb@smartsharesystems.com>,
dev@dpdk.org, david.marchand@redhat.com, thomas@monjalon.net
Subject: Re: [PATCH v2 1/2] eal: provide leading and trailing zero bit count abstraction
Date: Wed, 5 Apr 2023 09:44:54 +0100 [thread overview]
Message-ID: <ZC01Bm8eR/ADVsZj@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <20230404212322.GA3609@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
On Tue, Apr 04, 2023 at 02:23:22PM -0700, Tyler Retzlaff wrote:
> On Thu, Jan 05, 2023 at 08:09:19AM +0100, Morten Brørup wrote:
> > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > > Sent: Thursday, 24 November 2022 00.43
> > >
> > > Provide an abstraction for leading and trailing zero bit counting
> > > functions to hide compiler specific intrinsics and builtins.
> > >
> > > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > ---
> > > lib/eal/include/meson.build | 1 +
> > > lib/eal/include/rte_bitcount.h | 265
> > > +++++++++++++++++++++++++++++++++++++++++
> > > 2 files changed, 266 insertions(+)
> > > create mode 100644 lib/eal/include/rte_bitcount.h
> > >
> > > diff --git a/lib/eal/include/meson.build b/lib/eal/include/meson.build
> > > index cfcd40a..8ff1d65 100644
> > > --- a/lib/eal/include/meson.build
> > > +++ b/lib/eal/include/meson.build
> > > @@ -5,6 +5,7 @@ includes += include_directories('.')
> > >
> > > headers += files(
> > > 'rte_alarm.h',
> > > + 'rte_bitcount.h',
> > > 'rte_bitmap.h',
> > > 'rte_bitops.h',
> > > 'rte_branch_prediction.h',
> > > diff --git a/lib/eal/include/rte_bitcount.h
> > > b/lib/eal/include/rte_bitcount.h
> > > new file mode 100644
> > > index 0000000..587de52
> > > --- /dev/null
> > > +++ b/lib/eal/include/rte_bitcount.h
> > > @@ -0,0 +1,265 @@
> > > +/* SPDX-License-Identifier: BSD-3-Clause
> > > + * Copyright (C) 2022 Microsoft Corporation
> > > + */
> > > +
> > > +#ifndef _RTE_BITCOUNT_H_
> > > +#define _RTE_BITCOUNT_H_
> > > +
> > > +#include <rte_compat.h>
> > > +
> > > +#ifdef __cplusplus
> > > +extern "C" {
> > > +#endif
> > > +
> > > +#ifdef RTE_TOOLCHAIN_MSVC
> > > +
> > > +/**
> > > + * @warning
> > > + * @b EXPERIMENTAL: this API may change, or be removed, without prior
> > > notice
> > > + *
> > > + * Get the count of leading 0-bits in v.
> > > + *
> > > + * @param v
> > > + * The value.
> > > + * @return
> > > + * The count of leading zero bits.
> > > + */
> > > +__rte_experimental
> > > +static inline unsigned int
> > > +rte_clz(unsigned int v)
> > > +{
> > > + unsigned long rv;
> > > +
> > > + (void)_BitScanReverse(&rv, v);
> > > +
> > > + return (unsigned int)rv;
> > > +}
> > > +
> > > +/**
> > > + * @warning
> > > + * @b EXPERIMENTAL: this API may change, or be removed, without prior
> > > notice
> > > + *
> > > + * Get the count of leading 0-bits in v.
> > > + *
> > > + * @param v
> > > + * The value.
> > > + * @return
> > > + * The count of leading zero bits.
> > > + */
> > > +__rte_experimental
> > > +static inline unsigned int
> > > +rte_clzl(unsigned long v)
> >
> > Don't use l (long) and ll (long long) for names (and types), use explicit bit lengths, 32 and 64.
> >
> > E.g.: rte_clz32(uint32_t v)
>
> so i just noticed this, but sometimes these functions receive size_t so
> naming them specifically 32/64 bit becomes problematic because are going
> to end up with promotion on sizeof(size_t) == sizeof(long) == 4
> platforms.
>
> i.e.
> size_t s = ...;
> x = rte_clz64(s); // assume 64-bit today
>
> this code is now broken because on 32-bit platform s will get promoted
> and the extra 32 zero-bits will be returned in the result breaking
> calculations.
>
> any thoughts? should we go back to l, ll?
>
Yes, promotion will happen, but I still think that the 32 and 64 versions
are far clearer here in all cases. Anyone looking at the code will
recognise that the result will be the leading zero count of a 64-bit number
irrespective of the type actually passed in. It's less confusing now IMHO.
/Bruce
next prev parent reply other threads:[~2023-04-05 8:45 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-23 22:14 [PATCH 0/2] eal: provide leading and trailing zero bit count Tyler Retzlaff
2022-11-23 22:14 ` [PATCH 1/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-04-03 21:46 ` Mattias Rönnblom
2022-11-23 22:14 ` [PATCH 2/2] test/bitcount: add bitcount tests Tyler Retzlaff
2022-11-23 23:43 ` [PATCH v2 0/2] eal: provide leading and trailing zero bit count Tyler Retzlaff
2022-11-23 23:43 ` [PATCH v2 1/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2022-11-24 10:17 ` Morten Brørup
2022-11-28 17:13 ` Tyler Retzlaff
2022-11-28 17:22 ` Morten Brørup
2022-11-28 17:27 ` Tyler Retzlaff
2023-01-05 9:04 ` Thomas Monjalon
2023-01-05 17:23 ` Tyler Retzlaff
2023-01-05 17:27 ` Tyler Retzlaff
2023-01-05 20:57 ` Tyler Retzlaff
2023-01-05 21:34 ` Morten Brørup
2023-01-05 22:06 ` Tyler Retzlaff
2023-01-05 23:10 ` Morten Brørup
2023-01-06 1:04 ` Tyler Retzlaff
2023-01-06 10:09 ` Thomas Monjalon
2023-01-06 10:00 ` Thomas Monjalon
2023-01-05 7:09 ` Morten Brørup
2023-01-05 9:01 ` Thomas Monjalon
2023-01-05 17:21 ` Tyler Retzlaff
2023-01-06 0:32 ` Stephen Hemminger
2023-01-06 11:48 ` Bruce Richardson
2023-01-06 12:41 ` Morten Brørup
2023-01-06 13:40 ` Thomas Monjalon
2023-01-06 18:58 ` Tyler Retzlaff
2023-01-06 20:51 ` Thomas Monjalon
2023-01-10 9:18 ` Ferruh Yigit
2023-01-06 18:47 ` Tyler Retzlaff
2023-01-09 8:50 ` Bruce Richardson
2023-04-04 21:23 ` Tyler Retzlaff
2023-04-05 8:44 ` Bruce Richardson [this message]
2023-04-05 15:22 ` Tyler Retzlaff
2023-04-05 15:51 ` Bruce Richardson
2023-04-05 17:25 ` Tyler Retzlaff
2022-11-23 23:43 ` [PATCH v2 2/2] test/bitcount: add bitcount tests Tyler Retzlaff
2023-01-04 23:46 ` [PATCH v2 0/2] eal: provide leading and trailing zero bit count Tyler Retzlaff
2023-01-09 17:36 ` [PATCH v4 0/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-09 17:36 ` [PATCH v4 1/2] eal: move bit operation functions from common to bitops header Tyler Retzlaff
2023-01-10 13:56 ` Ferruh Yigit
2023-01-09 17:36 ` [PATCH v4 2/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-10 13:55 ` Ferruh Yigit
2023-01-10 17:34 ` Tyler Retzlaff
2023-01-10 18:37 ` Tyler Retzlaff
2023-01-10 13:56 ` [PATCH v4 0/2] " Ferruh Yigit
2023-01-06 22:01 ` [PATCH v3 0/3] eal: provide leading and trailing zero bit count Tyler Retzlaff
2023-01-06 22:01 ` [PATCH v3 1/3] eal: move bit functions from common to bitops header Tyler Retzlaff
2023-01-06 22:01 ` [PATCH v3 2/3] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-06 22:01 ` [PATCH v3 3/3] test/bitcount: add bitcount tests Tyler Retzlaff
2023-01-07 8:15 ` Thomas Monjalon
2023-01-09 16:57 ` Tyler Retzlaff
2023-01-09 17:26 ` Tyler Retzlaff
2023-01-07 13:40 ` Morten Brørup
2023-01-09 8:51 ` [PATCH v3 0/3] eal: provide leading and trailing zero bit count Bruce Richardson
2023-01-10 19:38 ` [PATCH v5 0/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-10 19:38 ` [PATCH v5 1/2] eal: move bit operation common to bitops header Tyler Retzlaff
2023-01-10 19:38 ` [PATCH v5 2/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-10 19:46 ` [PATCH v6 0/2] " Tyler Retzlaff
2023-01-10 19:46 ` [PATCH v6 1/2] eal: move bit operation common to bitops header Tyler Retzlaff
2023-01-10 19:46 ` [PATCH v6 2/2] eal: provide leading and trailing zero bit count abstraction Tyler Retzlaff
2023-01-20 22:14 ` [PATCH v6 0/2] " Tyler Retzlaff
2023-02-02 9:14 ` David Marchand
2023-02-02 10:56 ` David Marchand
2023-02-02 15:57 ` Tyler Retzlaff
2023-02-03 9:14 ` David Marchand
2023-02-02 15:56 ` Tyler Retzlaff
2023-02-03 9:21 ` David Marchand
2023-04-01 0:45 ` [PATCH v7 0/4] eal: provide abstracted bit counting functions Tyler Retzlaff
2023-04-01 0:45 ` [PATCH v7 1/4] eal: move bit count functions to bitops header Tyler Retzlaff
2023-04-01 0:45 ` [PATCH v7 2/4] eal: provide abstracted bit count functions Tyler Retzlaff
2023-04-01 0:45 ` [PATCH v7 3/4] pipeline: add include of bitops Tyler Retzlaff
2023-04-01 0:45 ` [PATCH v7 4/4] maintainers: add bitcount test under EAL API and common code Tyler Retzlaff
2023-04-01 7:08 ` [PATCH v7 0/4] eal: provide abstracted bit counting functions Morten Brørup
2023-04-04 0:11 ` [PATCH v8 0/3] " Tyler Retzlaff
2023-04-04 0:11 ` [PATCH v8 1/3] eal: move bit count functions to bitops header Tyler Retzlaff
2023-04-04 0:11 ` [PATCH v8 2/3] eal: provide abstracted bit count functions Tyler Retzlaff
2023-04-04 0:11 ` [PATCH v8 3/3] maintainers: add bitcount test under EAL API and common code Tyler Retzlaff
2023-04-04 8:27 ` [PATCH v8 0/3] eal: provide abstracted bit counting functions Bruce Richardson
2023-08-25 8:41 ` David Marchand
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