[PATCH v3 1/5] kernel: Add helper macros for loop unrolling

[Casey Schaufler]

On 9/18/2023 2:24 PM, KP Singh wrote:
> This helps in easily initializing blocks of code (e.g. static calls and
> keys).
>
> UNROLL(N, MACRO, __VA_ARGS__) calls MACRO N times with the first
> argument as the index of the iteration. This allows string pasting to
> create unique tokens for variable names, function calls etc.
>
> As an example:
>
> 	#include <linux/unroll.h>
>
> 	#define MACRO(N, a, b)            \
> 		int add_##N(int a, int b) \
> 		{                         \
> 			return a + b + N; \
> 		}
>
> 	UNROLL(2, MACRO, x, y)
>
> expands to:
>
> 	int add_0(int x, int y)
> 	{
> 		return x + y + 0;
> 	}
>
> 	int add_1(int x, int y)
> 	{
> 		return x + y + 1;
> 	}
>
> Signed-off-by: KP Singh <kpsingh at kernel.org>

I confess that I find some of the macros are scary, nonetheless

Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>

> ---
>  include/linux/unroll.h | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 include/linux/unroll.h
>
> diff --git a/include/linux/unroll.h b/include/linux/unroll.h
> new file mode 100644
> index 000000000000..d42fd6366373
> --- /dev/null
> +++ b/include/linux/unroll.h
> @@ -0,0 +1,36 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (C) 2023 Google LLC.
> + */
> +
> +#ifndef __UNROLL_H
> +#define __UNROLL_H
> +
> +#include <linux/args.h>
> +
> +#define UNROLL(N, MACRO, args...) CONCATENATE(__UNROLL_, N)(MACRO, args)
> +
> +#define __UNROLL_0(MACRO, args...)
> +#define __UNROLL_1(MACRO, args...)  __UNROLL_0(MACRO, args)  MACRO(0, args)
> +#define __UNROLL_2(MACRO, args...)  __UNROLL_1(MACRO, args)  MACRO(1, args)
> +#define __UNROLL_3(MACRO, args...)  __UNROLL_2(MACRO, args)  MACRO(2, args)
> +#define __UNROLL_4(MACRO, args...)  __UNROLL_3(MACRO, args)  MACRO(3, args)
> +#define __UNROLL_5(MACRO, args...)  __UNROLL_4(MACRO, args)  MACRO(4, args)
> +#define __UNROLL_6(MACRO, args...)  __UNROLL_5(MACRO, args)  MACRO(5, args)
> +#define __UNROLL_7(MACRO, args...)  __UNROLL_6(MACRO, args)  MACRO(6, args)
> +#define __UNROLL_8(MACRO, args...)  __UNROLL_7(MACRO, args)  MACRO(7, args)
> +#define __UNROLL_9(MACRO, args...)  __UNROLL_8(MACRO, args)  MACRO(8, args)
> +#define __UNROLL_10(MACRO, args...) __UNROLL_9(MACRO, args)  MACRO(9, args)
> +#define __UNROLL_11(MACRO, args...) __UNROLL_10(MACRO, args) MACRO(10, args)
> +#define __UNROLL_12(MACRO, args...) __UNROLL_11(MACRO, args) MACRO(11, args)
> +#define __UNROLL_13(MACRO, args...) __UNROLL_12(MACRO, args) MACRO(12, args)
> +#define __UNROLL_14(MACRO, args...) __UNROLL_13(MACRO, args) MACRO(13, args)
> +#define __UNROLL_15(MACRO, args...) __UNROLL_14(MACRO, args) MACRO(14, args)
> +#define __UNROLL_16(MACRO, args...) __UNROLL_15(MACRO, args) MACRO(15, args)
> +#define __UNROLL_17(MACRO, args...) __UNROLL_16(MACRO, args) MACRO(16, args)
> +#define __UNROLL_18(MACRO, args...) __UNROLL_17(MACRO, args) MACRO(17, args)
> +#define __UNROLL_19(MACRO, args...) __UNROLL_18(MACRO, args) MACRO(18, args)
> +#define __UNROLL_20(MACRO, args...) __UNROLL_19(MACRO, args) MACRO(19, args)
> +
> +#endif /* __UNROLL_H */