linux-kernel - Re: [PATCH v1 1/1] base64: Unroll the tables initialisers

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Message-ID: <20251103221857.1acaf6ab@pumpkin>
Date: Mon, 3 Nov 2025 22:18:57 +0000
From: David Laight <david.laight.linux@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Guan-Chun Wu
 <409411716@....tku.edu.tw>, Kuan-Wei Chiu <visitorckw@...il.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] base64: Unroll the tables initialisers

On Mon,  3 Nov 2025 20:05:10 +0100
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> Currently the initialisers of the tables have duplicate indices.
> This prevents from building with `make W=1`.
> 
> To address the issue, unroll the table initialisers with generated
> arrays by the following Python excerpt:
> 
> CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
> 
> def gen_table(ch62, ch63):
>     table = [ 0xff ] * 256
>     for idx, char in enumerate(CHARS):
>         table[ord(char)] = idx
>     table[ord(ch62)] = 62
>     table[ord(ch63)] = 63
> 
>     for i in range(0, len(table), 8):
>         print (f"\t{', '.join(f"0x{c:02x}" for c in table[i:i+8])},\t/* {i:-3d} - {i+7:-3d} */")
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  lib/base64.c | 115 +++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 102 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/base64.c b/lib/base64.c
> index bcdbd411d63b..0a7c15c5c1b6 100644
> --- a/lib/base64.c
> +++ b/lib/base64.c
> @@ -21,20 +21,109 @@ static const char base64_tables[][65] = {
>  	[BASE64_IMAP] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,",
>  };
>  
> -#define BASE64_REV_INIT(ch_62, ch_63) { \
> -	[0 ... 255] = -1, \
> -	['A'] =  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, \
> -		13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, \
> -	['a'] = 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, \
> -		39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, \
> -	['0'] = 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, \
> -	[ch_62] = 62, [ch_63] = 63, \
> -}
> -
>  static const s8 base64_rev_maps[][256] = {
> -	[BASE64_STD] = BASE64_REV_INIT('+', '/'),
> -	[BASE64_URLSAFE] = BASE64_REV_INIT('-', '_'),
> -	[BASE64_IMAP] = BASE64_REV_INIT('+', ',')
> +	[BASE64_STD] = {
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*   0 -   7 */

You need to use -1 not 0xff.

> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*   8 -  15 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*  16 -  23 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*  24 -  31 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*  32 -  39 */

Nothing wrong with [ 0 ... 39 ] = -1,

> +		0xff, 0xff, 0xff, 0x3e, 0xff, 0xff, 0xff, 0x3f,	/*  40 -  47 */
> +		0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,	/*  48 -  55 */
> +		0x3c, 0x3d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/*  56 -  63 */
> +		0xff, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,	/*  64 -  71 */
> +		0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,	/*  72 -  79 */
> +		0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,	/*  80 -  87 */
> +		0x17, 0x18, 0x19, 0xff, 0xff, 0xff, 0xff, 0xff,	/*  88 -  95 */
> +		0xff, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,	/*  96 - 103 */
> +		0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,	/* 104 - 111 */
> +		0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,	/* 112 - 119 */
> +		0x31, 0x32, 0x33, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 120 - 127 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 128 - 135 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 136 - 143 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 144 - 151 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 152 - 159 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 160 - 167 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 168 - 175 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 176 - 183 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 184 - 191 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 192 - 199 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 200 - 207 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 208 - 215 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 216 - 223 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 224 - 231 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 232 - 239 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 240 - 247 */
> +		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,	/* 248 - 255 */
> +	},
...

This is impenetrable crap...

	David