Ted Faber wrote:
On Mon, Jun 12, 2006 at 02:11:19PM +0200, Iljitsch van Beijnum wrote:
The problem with text is that you have to walk through memory and
compare characters. A LOT.
That's not where your code spends its time.
Run gprof(1). The majority of time your code spends is spent doing the
2 integer divides per text to integer conversion and in strtoimax
(called by fscanf).
Multiplying or dividing is the worst thing you can do on a CPU in
general.
Note that CPUs are different; some multiply faster than others, compared
to the rest of the HW.
And if you really need to, you can optimize... a multiplication by 10,
for instance, can be done by two left shifts and an addition (a*10 = a
<<3 + a<<1); I have no idea why strtoimax would do divisions, but I
haven't written decimal-number parsers for a very long time; I think
Knuth had 3 different ones in "Seminumerical algorithms", but that was a
VERY long time ago...
Harald
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