Re: [PATCH 6/12] random pt4: Replace SHA with faster version

[Denis Vlasenko]

On Friday 21 January 2005 23:41, Matt Mackall wrote:
> - * @W:      80 words of workspace
> + * @W:      80 words of workspace, caller should clear

Why?

>   *
>   * This function generates a SHA1 digest for a single. Be warned, it
>   * does not handle padding and message digest, do not confuse it with
>   * the full FIPS 180-1 digest algorithm for variable length messages.
>   */
> -void sha_transform(__u32 *digest, const char *data, __u32 *W)
> +void sha_transform(__u32 *digest, const char *in, __u32 *W)
>  {
> -	__u32 A, B, C, D, E;
> -	__u32 TEMP;
> -	int i;
> +	__u32 a, b, c, d, e, t, i;
>  
> -	memset(W, 0, sizeof(W));
>  	for (i = 0; i < 16; i++)
> -		W[i] = be32_to_cpu(((const __u32 *)data)[i]);
> -	/*
> -	 * Do the preliminary expansion of 16 to 80 words.  Doing it
> -	 * out-of-line line this is faster than doing it in-line on
> -	 * register-starved machines like the x86, and not really any
> -	 * slower on real processors.
> -	 */
> -	for (i = 0; i < 64; i++) {
> -		TEMP = W[i] ^ W[i+2] ^ W[i+8] ^ W[i+13];
> -		W[i+16] = rol32(TEMP, 1);
> +		W[i] = be32_to_cpu(((const __u32 *)in)[i]);
> +
> +	for (i = 0; i < 64; i++)
> +		W[i+16] = rol32(W[i+13] ^ W[i+8] ^ W[i+2] ^ W[i], 1);
--
vda

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