Dmitry K. wrote:
On Wednesday 12 December 2007 01:16, Albert Andras wrote:
- Original Message -
From: Nathan Moore [EMAIL PROTECTED]
unsigned char a, b, c;
c = some_input_function();
LABEL:
a = c/10;
b = c%10;
...
*
LABEL:
mov r24,r18
ldi
Gre7g Luterman wrote:
[...]
Well if size speed are getting you down, try this:
http://pastie.textmate.org/127218
The calculation takes 22 bytes and executes in 40
clocks. As an assembly-language programmer, having
that extra MOV in the beginning annoys me, but hey, I
try not to break the asm
Thank you for your explination Bjoern.
I have looked at GCC internals before, but never worked on them, so I'm
likely to say something stupid.
I would have thought that an optimization pattern for just this type of
thing would have already been in GCC, especially since on the internal
helper
Paulo Marques wrote:
[...]
a = (c * 65534) 16;
b = c - (a * 10);
leaving you with no divisions to perform.
The main problem is that the first multiplication should be done with
some hand optimized assembly to perform a 8x16 bit multiplication,
leaving just the upper 8 bits of a 24 bit
-Original Message-
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
org] On Behalf Of Nathan Moore
Sent: Tuesday, December 11, 2007 9:26 AM
To: avr-gcc-list@nongnu.org
Subject: RE: [avr-gcc-list] dev and mod may not be optimized
Thank you for your explination Bjoern.
I
--- Paulo Marques [EMAIL PROTECTED] wrote:
Actually after a few more digging, we can do this
all in plain C, by
using a smaller reciprocal multiplier:
snipped
Wow, that's freakin' inspired! And you're right it
does optimize nicely. Here's a 20 byte version that
executes in 12 cycles:
Gre7g Luterman wrote:
--- Paulo Marques [EMAIL PROTECTED] wrote:
Actually after a few more digging, we can do this
all in plain C, by
using a smaller reciprocal multiplier:
snipped
Wow, that's freakin' inspired!
Thanks :)
It's not really a new idea, though. Using multiply by the
Just a correction : div() take 2 parameters :
div_t t;
t=div(c, 10);
a=t.quot;
b=t.rem;
Eric.
- Original Message -
From: Albert Andras
To: avr-gcc-list@nongnu.org
Sent: Tuesday, December 11, 2007 4:16 PM
Subject: Re: [avr-gcc-list] dev and mod may
On Wednesday 12 December 2007 01:16, Albert Andras wrote:
- Original Message -
From: Nathan Moore [EMAIL PROTECTED]
unsigned char a, b, c;
c = some_input_function();
LABEL:
a = c/10;
b = c%10;
...
*
LABEL:
mov r24,r18
ldi
-Original Message-
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
org] On Behalf Of Dmitry K.
Sent: Tuesday, December 11, 2007 3:44 PM
To: avr-gcc-list@nongnu.org
Cc: Nathan Moore
Subject: Re: [avr-gcc-list] dev and mod may not be optimized
Alas, the usage of div
--- Dmitry K. [EMAIL PROTECTED] wrote:
Alas, the usage of div() function is more space and
more time
expansive. The reason is that div() uses an another
function:
__divmodhi4(), i.e. 16-bits.
Compare two programs:
prog1: 150 bytes, 238 clocks
prog2: 212 bytes, 316 clocks
Well if
On Wednesday 12 December 2007 09:29, Weddington, Eric wrote:
Should we implement 2 (or 3) div functions then in avr-libc? 8, 16, and
32 bit?
Possible, yes. Today the libgcc labrary contains 6 division
functions (8, 16, 32 bits, signed and unsigned), but Avr-libc
includes only 2 links (div,
-Original Message-
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]
org] On Behalf Of Dmitry K.
Sent: Tuesday, December 11, 2007 5:37 PM
To: avr-gcc-list@nongnu.org
Subject: Re: [avr-gcc-list] dev and mod may not be optimized
On Wednesday 12 December 2007 09:29, Weddington
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