RE: [avr-gcc-list] 10 bit division in AVR-GCC

[Dean Ferreyra]

Uwe,

About 9 months ago I wrote a small AVR program to time various operations.
Here are the results I got:

atmega103 at 4 MHz

             Hz     Cycles

Overhead:
; (u):       190378    21

uint8_t:
x+y (u):     142747     7
x-y (u):     142762     7
x<<5 (u):    142762     7
x*y (o):      46497    65
x/y (o):      37026    87
x%y (o):      36686    88

uint16_t:
x+y (u):     114218    14
x-y (u):     114225    14
x<<9 (u):    124927    11
x*y (o):      19412   185
x/y (o):      16662   219
x%y (o):      16802   217
div (o):      14436   256

uint32_t:
x+y (u):      81598    28
x-y (u):      81601    28
x<<17 (o):    25633   135
x*y (o):       9214   413
x/y (o):       6105   634
x%y (o):       6105   634
ldiv (o):      5228   744

uint64_t:
x+y (o):      26481   130
x-y (o):      26482   130
x*y (o):       2936  1341
x<<33 (o):    13510   275
x/y (o):       1040  3825
x%y (o):        977  4073

float:
fabs (u):    105206    17
floor (o):     7810   491
ceil (o):      7918   484
x+y (o):      27578   124
x-y (o):      22592   156
x*y (o):       9387   405
x/y (o):       7310   526
inverse (o):   7297   527
square (o):    9566   397
sqrt (o):      2366  1670
cos (o):        801  4973
sin (o):        716  5566
tan (o):        699  5701
pow (o):        379 10533
exp (o):        920  4327
log (o):        688  5793
log10 (o):      633  6298
acos (o):       702  5677
asin (o):       719  5542

The Hz column is how many of the given operations the AVR was able to do in
one second.  The Cycles column is how many cycles it took to do the
operation once.  The Cycles column takes overhead into account with the
overhead calculated in the first test (labeled ";", i.e. an empty C line).
(For example, the test of "tan" above can be performed 699 times in one
second, so it takes 4 MHz / 699 = 5722 cycles per operation.  Since the
overhead is 21 cycles, the result you see is 5701 cycles.)  Each operation
was run 65536 times or until a timer overflowed, whichever came first.  (The
"u" or "o" in the parentheses indicate whether or not the timer overflowed.)

I did this to get in the ballpark and kept this list handy when making
descisions on how to implement my algorithms.

Dean

-----Original Message-----
From: address@hidden [mailto:address@hidden
Behalf Of Uwe Bonnes
Sent: Wednesday, May 22, 2002 1:31 AM
To: address@hidden
Subject: [avr-gcc-list] 10 bit division in AVR-GCC


Hallo,

does a 10(16) bit divide work out of the box with AVR-GCC and avr-lib?
Approx how long does it take with 8 MHz? Is the Hardware Multiplier
(recent AtMegas) of help for the division?

Thanks
--
Uwe Bonnes                address@hidden

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
avr-gcc-list at http://avr1.org

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