Messages in this thread | | | From | Michal Nazarewicz <> | Subject | Re: [PATCH 3/4] lib: vsprintf: Optimize put_dec_trunc8 | Date | Sun, 23 Sep 2012 20:22:02 +0200 |
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On Fri, Aug 03 2012, George Spelvin wrote: > If you're going to have a conditional branch after > each 32x32->64-bit multiply, might as well shrink the code > and make it a loop. > > This also avoids using the long multiply for small integers. > > (This leaves the comments in a confusing state, but that's a separate > patch to make review easier.) > > Signed-off-by: George Spelvin <linux@horizon.com>
NAK.
> --- > lib/vsprintf.c | 20 ++++++-------------- > 1 file changed, 6 insertions(+), 14 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index a8e7392..3ca77b8 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -174,20 +174,12 @@ char *put_dec_trunc8(char *buf, unsigned r) > unsigned q; > > /* Copy of previous function's body with added early returns */ > - q = (r * (uint64_t)0x1999999a) >> 32; > - *buf++ = (r - 10 * q) + '0'; /* 2 */ > - if (q == 0) > - return buf; > - r = (q * (uint64_t)0x1999999a) >> 32; > - *buf++ = (q - 10 * r) + '0'; /* 3 */ > - if (r == 0) > - return buf; > - q = (r * (uint64_t)0x1999999a) >> 32; > - *buf++ = (r - 10 * q) + '0'; /* 4 */ > - if (q == 0) > - return buf; > - r = (q * (uint64_t)0x1999999a) >> 32; > - *buf++ = (q - 10 * r) + '0'; /* 5 */ > + while (r >= 10000) { > + q = r + '0'; > + r = (r * (uint64_t)0x1999999a) >> 32; > + *buf++ = q - 10*r; > + }
This loop looks nothing like the original code. Why are you adding '0' at the beginning? Also, the original code switches the role of q and r, the loop does not.
> if (r == 0) > return buf; > q = (r * 0x199a) >> 16;
-- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--[unhandled content-type:application/pgp-signature] | |