[PATCH v2 2/5] lib/eal: add portable version of __builtin_add_overflow

[Bruce Richardson]

On Fri, Jan 03, 2025 at 12:39:38PM -0800, Andre Muezerie wrote:
> __builtin_add_overflow is gcc specific. There's a need for a portable
> version that can also be used with other compilers.
> 
> This patch introduces rte_add_overflow.
> 
> Signed-off-by: Andre Muezerie <andremue at linux.microsoft.com>
> ---
>  lib/eal/include/meson.build |  1 +
>  lib/eal/include/rte_math.h  | 46 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
>  create mode 100644 lib/eal/include/rte_math.h
> 
> diff --git a/lib/eal/include/meson.build b/lib/eal/include/meson.build
> index d903577caa..041a4105b5 100644
> --- a/lib/eal/include/meson.build
> +++ b/lib/eal/include/meson.build
> @@ -31,6 +31,7 @@ headers += files(
>          'rte_lcore_var.h',
>          'rte_lock_annotations.h',
>          'rte_malloc.h',
> +        'rte_math.h',
>          'rte_mcslock.h',
>          'rte_memory.h',
>          'rte_memzone.h',
> diff --git a/lib/eal/include/rte_math.h b/lib/eal/include/rte_math.h
> new file mode 100644
> index 0000000000..2f4581f81b
> --- /dev/null
> +++ b/lib/eal/include/rte_math.h
> @@ -0,0 +1,46 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2025 Microsoft Corporation
> + */
> +
> +#ifndef _RTE_MATH_H_
> +#define _RTE_MATH_H_
> +
> +/**
> + * @file
> + *
> + * Math function definitions for DPDK.
> + */
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +/*
> + * Function that allows performing simple arithmetic operations together with
> + * checking whether the operation overflowed.
> + * Example of usage:
> + *     uint8_t overflow;
> + *     uint16_t a, b, result;
> + *     a = 1;
> + *     b = 2;
> + *     overflow = rte_add_overflow(a, b, &result);
> + */
> +#ifdef RTE_TOOLCHAIN_MSVC
> +#define rte_add_overflow(a, b, res) _Generic((a), \
> +	uint8_t : _addcarry_u8, \
> +	uint16_t : _addcarry_u16, \
> +	uint32_t : _addcarry_u32, \
> +	uint64_t : _addcarry_u64)(0, a, b, res)
> +#else
> +#define rte_add_overflow(a, b, res) _Generic((a), \
> +	uint8_t : __builtin_add_overflow, \
> +	uint16_t : __builtin_add_overflow, \
> +	uint32_t : __builtin_add_overflow, \
> +	uint64_t : __builtin_add_overflow)(a, b, res)
> +#endif

For the gcc version, can you just simplify to the one-line below?

#define rte_add_overflow __builtin_add_overflow

/Bruce