From: Omar Polo <op@omarpolo.com>
Subject: Re: provide functions to parse/serialize different hashes
To: Christian Weisgerber <naddy@mips.inka.de>
Cc: gameoftrees@openbsd.org
Date: Thu, 23 Feb 2023 20:17:36 +0100

On 2023/02/23 20:12:15 +0100, Christian Weisgerber <naddy@mips.inka.de> wrote:
> Omar Polo:
> 
> > +static char *
> > +digest_to_str(const uint8_t *digest, int len, char *buf)
> >  {
> >  	char *p = buf;
> >  	char hex[3];
> >  	int i;
> >  
> > -	if (size < SHA1_DIGEST_STRING_LENGTH)
> > -		return NULL;
> > -
> > -	for (i = 0; i < SHA1_DIGEST_LENGTH; i++) {
> > +	for (i = 0; i < len; i++) {
> >  		snprintf(hex, sizeof(hex), "%.2x", digest[i]);
> >  		p[0] = hex[0];
> >  		p[1] = hex[1];
> 
> Calling snprintf() 20 or soon 32 times to format a hash seems
> excessive.  How about doing this the very old-fashioned way?

Agreed, and fwiw I like it a lot, thanks!  OK with me

> diff /home/naddy/got
> commit - 87a3ab84d3eb87b790e3d34aeec2c344a8d7375b
> path + /home/naddy/got
> blob - 51a9a0ca1ab1e8d6bc5e9f6722d0595f2a3b5fe7
> file + lib/hash.c
> --- lib/hash.c
> +++ lib/hash.c
> @@ -71,17 +71,15 @@ digest_to_str(const uint8_t *digest, int len, char *bu
>  static char *
>  digest_to_str(const uint8_t *digest, int len, char *buf)
>  {
> +	const char hex[] = "0123456789abcdef";
>  	char *p = buf;
> -	char hex[3];
>  	int i;
>  
>  	for (i = 0; i < len; i++) {
> -		snprintf(hex, sizeof(hex), "%.2x", digest[i]);
> -		p[0] = hex[0];
> -		p[1] = hex[1];
> -		p += 2;
> +		*p++ = hex[digest[i] >> 4];
> +		*p++ = hex[digest[i] & 0xf];
>  	}
> -	p[0] = '\0';
> +	*p = '\0';
>  
>  	return buf;
>  }