Re: [PATCH 2/5] hashmap: allow memihash computation to be continued

From: Junio C Hamano <gitster@pobox.com>
Date: Feb 18, 2017, 05:35 UTC
Message-ID: <xmqq7f4onjrs.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <bd4893f86c4484fc36480848bf2d0905d961e022.1487071883.git.johannes.schindelin@gmx.de>

Johannes Schindelin <johannes.schindelin@gmx.de> writes:

Show 21 quoted lines

> diff --git a/hashmap.c b/hashmap.c
> index b10b642229c..061b7d61da6 100644
> --- a/hashmap.c
> +++ b/hashmap.c
> @@ -50,6 +50,20 @@ unsigned int memihash(const void *buf, size_t len)
>  	return hash;
>  }
>  
> +/* Incoporate another chunk of data into a memihash computation. */
> +unsigned int memihash_continue(unsigned int hash,
> +			       const void *buf, size_t len)
> +{
> +	const unsigned char *p = buf;
> +	while (len--) {
> +		unsigned int c = *p++;
> +		if (c >= 'a' && c <= 'z')
> +			c -= 'a' - 'A';
> +		hash = (hash * FNV32_PRIME) ^ c;
> +	}
> +	return hash;
> +}

This makes me wonder if we want to reduce the duplication (primarily to avoid risking the loop body to go out of sync) by doing:

	unsigned int memihash(const void *buf, size_t len)
	{
		return memihash_continue(buf, len, FNV32_BASE);
	}

If an extra call level really matters, its "inline" equivalent in the header would probably be good.