# [PATCH] delta micro optimization 3 messages from 2006-02-10 to 2006-02-10. Participants: Nicolas Pitre, Junio C Hamano. Thread: https://gitlist.dev/t/3285 ## Nicolas Pitre, 2006-02-10 18:42 Subject: [PATCH] delta micro optimization Message-ID: URL: https://gitlist.dev/e/Pine.LNX.4.64.0602101335160.5397%40localhost.localdomain ``` My kernel work habit made me look at the generated assembly for the delta code, and one obvious albeit small improvement is this patch. Signed-off-by: Nicolas Pitre --- diff --git a/delta.h b/delta.h index 31d1820..a15350d 100644 --- a/delta.h +++ b/delta.h @@ -19,14 +19,14 @@ extern void *patch_delta(void *src_buf, static inline unsigned long get_delta_hdr_size(const unsigned char **datap) { const unsigned char *data = *datap; - unsigned char cmd = *data++; - unsigned long size = cmd & ~0x80; - int i = 7; - while (cmd & 0x80) { + unsigned char cmd; + unsigned long size = 0; + int i = 0; + do { cmd = *data++; size |= (cmd & ~0x80) << i; i += 7; - } + } while (cmd & 0x80); *datap = data; return size; } ``` ## Junio C Hamano, 2006-02-10 20:00 Subject: Re: [PATCH] delta micro optimization Message-ID: <7vhd77vv9o.fsf@assigned-by-dhcp.cox.net> URL: https://gitlist.dev/e/7vhd77vv9o.fsf%40assigned-by-dhcp.cox.net In-Reply-To: ``` That looks obviously correct but it really is micro. Have you benched it? On which architectures? Does it help everywhere or register starved ones benefit more than others? ``` ## Nicolas Pitre, 2006-02-10 20:38 Subject: Re: [PATCH] delta micro optimization Message-ID: URL: https://gitlist.dev/e/Pine.LNX.4.64.0602101516310.5397%40localhost.localdomain In-Reply-To: <7vhd77vv9o.fsf@assigned-by-dhcp.cox.net> ``` On Fri, 10 Feb 2006, Junio C Hamano wrote: > That looks obviously correct but it really is micro. Have you > benched it? On which architectures? Does it help everywhere or > register starved ones benefit more than others? I doubt the performance difference would be measurable on i386 although the code is a bit smaller. On ARM it causes a code reduction of 12.5% in count-delta.o. Nicolas ```