linux-kernel - Re: [PATCH] bitops: simplify get_count_order

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Message-Id: <20200527160508.2ef29d6904c07ca6c650638c@linux-foundation.org>
Date:   Wed, 27 May 2020 16:05:08 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        christian.brauner@...ntu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bitops: simplify get_count_order_long()

On Wed, 27 May 2020 22:45:42 +0000 Wei Yang <richard.weiyang@...il.com> wrote:

> /* a tiny module only meant to test get_count_order/long */
> unsigned int order_comb[][2] = {
> 	{0x00000003,  2},
> 	{0x00000004,  2},
> 	{0x00001fff, 13},
> 	{0x00002000, 13},
> 	{0x50000000, 32},
> 	{0x80000000, 32},
> };
> 
> static int __init test_getorder_startup(void)
> {
> 	int i;
> 
> 	for (i = 0; i < ARRAY_SIZE(order_comb); i++) {
> 		if (order_comb[i][1] != get_count_order(order_comb[i][0]))
> 			pr_warn("get_count_order wrong for %lx\n",
> 					order_comb[i][0]);
> 	}
> 
> 	return 0;
> }
> 
> Since I don't get a way to iterate all the possibilities, some random
> combination is chosen. Is this one looks good?

Looks good.

You might want to add a less-negative number as well?  0x80030000. 
Something that won't turn positive if it has 1 subtracted from it.