[PATCH edid-decode v2 1/2] Make do_checksum reusable for DisplayID checksums.

[walter harms]

look good for me.

Reviewed-by: wharms at bfs.de


Am 06.02.2017 14:51, schrieb Mark Ferry:
> DisplayID, unlike EDID and CEA, is a variable length structure.
> Allow for reuse of do_checksum by adding a length parameter.
> 
> Return a boolean to allow the caller to record failure.
> ---
>  edid-decode.c | 45 ++++++++++++++++++++++++++++-----------------
>  1 file changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/edid-decode.c b/edid-decode.c
> index c18697f..15660dc 100644
> --- a/edid-decode.c
> +++ b/edid-decode.c
> @@ -34,6 +34,10 @@
>  
>  #define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
>  
> +enum {
> +    EDID_PAGE_SIZE = 128u
> +};
> +
>  static int claims_one_point_oh = 0;
>  static int claims_one_point_two = 0;
>  static int claims_one_point_three = 0;
> @@ -208,7 +212,7 @@ detailed_cvt_descriptor(unsigned char *x, int first)
>  static char *
>  extract_string(unsigned char *x, int *valid_termination, int len)
>  {
> -    static char ret[128];
> +    static char ret[EDID_PAGE_SIZE];
>      int i, seen_newline = 0;
>  
>      memset(ret, 0, sizeof(ret));
> @@ -560,21 +564,25 @@ detailed_block(unsigned char *x, int in_extension)
>      return 1;
>  }
>  
> -static void
> -do_checksum(unsigned char *x)
> +static int
> +do_checksum(unsigned char *x, size_t len)
>  {
> -    printf("Checksum: 0x%hx", x[0x7f]);
> -    {
> -	unsigned char sum = 0;
> -	int i;
> -	for (i = 0; i < 128; i++)
> -	    sum += x[i];
> -	if (sum) {
> -	    printf(" (should be 0x%hx)", (unsigned char)(x[0x7f] - sum));
> -	    has_valid_checksum = 0;
> -	} else printf(" (valid)");
> +    unsigned char check = x[len - 1];
> +    unsigned char sum = 0;
> +    int i;
> +
> +    printf("Checksum: 0x%hx", check);
> +
> +    for (i = 0; i < len-1; i++)
> +        sum += x[i];
> +
> +    if ((unsigned char)(check + sum) != 0) {
> +        printf(" (should be 0x%hx)\n", -sum & 0xff);
> +        return 0;
>      }
> -    printf("\n");
> +
> +    printf(" (valid)\n");
> +    return 1;
>  }
>  
>  /* CEA extension */
> @@ -1281,7 +1289,7 @@ parse_cea(unsigned char *x)
>  		detailed_block(detailed, 1);
>      } while (0);
>  
> -    do_checksum(x);
> +    do_checksum(x, EDID_PAGE_SIZE);
>  
>      return ret;
>  }
> @@ -1371,6 +1379,9 @@ parse_displayid(unsigned char *x)
>      int ext_count = x[4];
>      int i;
>      printf("Length %d, version %d, extension count %d\n", length, version, ext_count);
> +
> +    do_checksum(x+1, length + 5);
> +
>      int offset = 5;
>      while (length > 0) {
>         int tag = x[offset];
> @@ -2037,11 +2048,11 @@ int main(int argc, char **argv)
>  	has_valid_extension_count = 1;
>      }
>  
> -    do_checksum(edid);
> +    do_checksum(edid, EDID_PAGE_SIZE);
>  
>      x = edid;
>      for (edid_lines /= 8; edid_lines > 1; edid_lines--) {
> -	x += 128;
> +	x += EDID_PAGE_SIZE;
>  	nonconformant_extension += parse_extension(x);
>      }
>  
> 
> 
> 
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