[PATCH v2 1/2] eal: provide leading and trailing zero bit count abstraction

[Morten Brørup]

> From: Tyler Retzlaff [mailto:roretzla at 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 at 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)

> +{
> +	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_clzll(unsigned long long v)

Same comment as above: e.g. rte_clz64(uint64_t v)