Re: [PATCH 4/5] gzip: move crc state into consilidated gzip state

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/04/2024 4:25 pm, Daniel P. Smith wrote:
> diff --git a/xen/common/gzip/inflate.c b/xen/common/gzip/inflate.c
> index c8dd35962abb..6c8c7452a31f 100644
> --- a/xen/common/gzip/inflate.c
> +++ b/xen/common/gzip/inflate.c
> @@ -1125,16 +1125,14 @@ static int __init inflate(struct gzip_data *gd)
>   *
>   **********************************************************************/
>  
> -static ulg __initdata crc_32_tab[256];
> -static ulg __initdata crc;  /* initialized in makecrc() so it'll reside in 
> bss */
> -#define CRC_VALUE (crc ^ 0xffffffffUL)
> +#define CRC_VALUE (gd->crc ^ 0xffffffffUL)
>  
>  /*
>   * Code to compute the CRC-32 table. Borrowed from
>   * gzip-1.0.3/makecrc.c.
>   */
>  
> -static void __init makecrc(void)
> +static void __init makecrc(struct gzip_data *gd)
>  {
>  /* Not copyrighted 1990 Mark Adler */
>  
> @@ -1151,7 +1149,7 @@ static void __init makecrc(void)
>      for (i = 0; i < sizeof(p)/sizeof(int); i++)
>          e |= 1L << (31 - p[i]);
>  
> -    crc_32_tab[0] = 0;
> +    gd->crc_32_tab[0] = 0;
>  
>      for (i = 1; i < 256; i++)
>      {
> @@ -1162,11 +1160,11 @@ static void __init makecrc(void)
>              if (k & 1)
>                  c ^= e;
>          }
> -        crc_32_tab[i] = c;
> +        gd->crc_32_tab[i] = c;
>      }
>  
>      /* this is initialized here so this code could reside in ROM */
> -    crc = (ulg)0xffffffffUL; /* shift register contents */
> +    gd->crc = (ulg)0xffffffffUL; /* shift register contents */
>  }
>  
>  /* gzip flag byte */

I can't see any way that a non-32bit value ever gets stored, because 'e'
doesn't ever have bit 32 set in it.  I have a sneaking suspicion that
this is code written in the 32bit days, where sizeof(long) was still 4.

This change, if correct, halves the size of gzip_state.

~Andrew