I'm deciding on a language to use for back-end use. I've looked at Go, Rust, C++, and I thought I'd look at Crystal because it did reasonably well in some benchmarks. Speed is not the ultimate requirement, however speed is important. The syntax is equally important, and I'm not averse to the Crystal syntax. The simple benchmark that I wrote is only a small part of the evaluation and it's also partly familiarisation. I'm using Windows, so I'm using Crystal 0.35.1 on Win10 2004-19041.329 with WSL2 and Ubuntu 20.04 LTS. I don't know if WSL2 has any impact on performance. The benchmark is primarily using integer arithmetic. Go, Rust, and C++ have almost equal performance to each other (on Win10). I've translated that code to Crystal, and it runs a fair bit slower than those three. Out of simple curiosity I also ran the code on Dart (on Win10), and it ran (very surprisingly) almost twice as fast as those three. I do understand that a simple benchmark does not say a lot. I notice from a recent post that Crystal is more efficient with floats than integers, however this was and is aimed at integers.
This is my first Crystal program, so I thought I should ask - is there any simple improvements I can make to the code for performance? I don't want to improve the algorithm other than to correct errors, because all are using this algorithm.
The code is as follows:
# ------ Prime-number counter. -----#
# Brian 25-Jun-2020 Program written - my first Crystal program.
# -------- METHOD TO CALCULATE APPROXIMATE SQRT ----------#
def fnCalcSqrt(iCurrVal) # Calculate approximate sqrt
iPrevDiv = 0.to_i64
iDiv = (iCurrVal // 10)
if iDiv < 2
iDiv = 2
end
while (true)
begin
iProd = (iDiv * iDiv)
rescue vError
puts "Error = #{vError}, iDiv = #{iDiv}, iCurrVal = #{iCurrVal}"
exit
end
if iPrevDiv < iDiv
iDiff = ((iDiv - iPrevDiv) // 2)
else
iDiff = ((iPrevDiv - iDiv) // 2)
end
iPrevDiv = iDiv
if iProd < iCurrVal # iDiv IS TOO LOW #
if iDiff < 1
iDiff = 1
end
iDiv += iDiff
else
if iDiff < 2
return iDiv
end
iDiv -= iDiff
end
end
end
# ---------- PROGRAM MAINLINE --------------#
print "\nCalculate Primes from 1 to selected number"
#iMills = uninitialized Int32 # CHANGED THIS BECAUSE IN --release DOES NOT WORK
iMills = 0.to_i32
while iMills < 1 || iMills > 100
print "\nEnter the ending number of millions (1 to 100) : "
sInput = gets
if sInput == ""
exit
end
iTemp = sInput.try &.to_i32?
if !iTemp
puts "Please enter a valid number"
puts "iMills = #{iTemp}"
elsif iTemp > 100 # > 100m
puts "Invalid - too big must be from 1 to 100 (million)"
elsif iTemp < 1
puts "Invalid - too small - must be from 1 to 100 (million)"
else
iMills = iTemp
end
end
#iCurrVal = 2 # THIS CAUSES ARITHMETIC OVERFLOW IN SQRT CALC.
iCurrVal = 2.to_i64
iEndVal = iMills * 1_000_000
iPrimeTot = 0
# ----- START OF PRIME NUMBER CALCULATION -----#
sEndVal = iEndVal.format(',', group: 3) # => eg. "10,000,000"
puts "Calculating number of prime numbers from 2 to #{sEndVal} ......"
vStartTime = Time.monotonic
while iCurrVal <= iEndVal
if iCurrVal % 2 != 0 || iCurrVal == 2
iSqrt = fnCalcSqrt(iCurrVal)
tfPrime = true # INIT
iDiv = 2
while iDiv <= iSqrt
if ((iCurrVal % iDiv) == 0)
tfPrime = (iDiv == iCurrVal);
break;
end
iDiv += 1
end
if (tfPrime)
iPrimeTot+=1;
end
end
iCurrVal += 1
end
puts "Elapsed time = #{Time.monotonic - vStartTime}"
puts "prime total = #{iPrimeTot}"
You need to compile with --release flag. By default, the Crystal compiler is focused on compilation speed, so you get a compiled program fast. This is particularly important during development. If you want a program that runs fast, you need to pass the --release flag which tells the compiler to take time for optimizations (that's handled by LLVM btw.).
You might also be able to shave off some time by using wrapping operators like &+ in location where it's guaranteed that the result can'd overflow. That skips some overflow checks.
A few other remarks:
Instead of 0.to_i64, you can just use a Int64 literal: 0_i64.
iMills = uninitialized Int32
Don't use uninitialized here. It's completely wrong. You want that variable to be initialized. There are some use cases for uninitialized in C bindings and some very specific, low-level implementations. It should never be used in most regular code.
I notice from a recent post that Crystal is more efficient with floats than integers
Where did you read that?
Adding type prefixes to identifiers doesn't seem to be very useful in Crystal. The compiler already keeps track of the types. You as the developer shouldn't have to do that, too. I've never seen that before.
Assertion of condition is well known way to design application in strategic way. You could be completely sure that your code will work correctly a day after release, but also when other dev in your team will change this code.
There are 2 common ways to put assertion in Lua code:
assert(1 > 0, "Assert that math works")
if 1 <= 0 then
error("Assert that math doesn't work")
end
I would expect this thing similar from performance point of view.
Consider it only matter of style. But it happens to be not true.
assert works longer on my machine:
function with_assert()
for i=1,100000 do
assert(1 < 0, 'Assert')
end
end
function with_error()
for i=1,100000 do
if 1 > 0 then
error('Error')
end
end
end
local t = os.clock()
pcall(with_assert)
print(os.clock() - t)
t = os.clock()
pcall(with_error)
print(os.clock() - t)
>> 3.1999999999999e-05
>> 1.5e-05
Why does it happen?
Look at the source code of assert and error: assert does some work and then calls error.
But the loop in your code serves no purpose: throwing an error during the first iteration means that the rest of the iterations don't run. Perhaps you meant to put the loop around the pcalls as below. Then you'll find hardly any difference between the times.
function with_assert()
assert(1 < 0, 'Assert')
end
function with_error()
if 1 > 0 then
error('Error')
end
end
function test(f)
local t = os.clock()
for i=1,100000 do
pcall(f)
end
print(os.clock() - t)
end
test(with_assert)
test(with_error)
I am trying to implement binary16 encoding for a half-precision floating point type.
The code is working except for one detail: It returns an object with the three properties (sign, exponent, fraction), but I would like it to return the float. Right now, I have to call to_f to get to the float. I would like this to work the way the integrated int and float classes work.
Here's my code:
require 'bindata'
class Binary16Be < BinData::Record
# naming based on https://en.wikipedia.org/wiki/Half-precision_floating-point_format
bit1 :sign_bit
bit5 :exponent
bit10 :fraction
def sign
sign_bit.zero? ? 1 : -1
end
def to_f
if exponent == 31 # special value in binary16 - all exponent bits are 1
return fraction.zero? ? (sign * Float::INFINITY) : Float::NAN
end
sign * 2**(exponent - 15) * (1.0 + fraction.to_f / 1024)
end
end
What I would like:
Binary16Be.read("\x3C\x00")
=> 1.0
What happens right now:
Binary16Be.read("\x3C\x00")
{:sign_bit=>0, :exponent=>15, :fraction=>0}
(this is not actually my own answer, I received this from the gem's author. Made slight alterations to his answer to fit this Q&A format a little better.)
The procedure is described in the bindata Wiki / Primitive Types
In your case:
Subclass Primitive instead of Record
Rename #to_f to #get
Implement #set
The converted code
class Binary16Be < BinData::Primitive
# naming based on
# https://en.wikipedia.org/wiki/Half-precision_floating-point_format
bit1 :sign_bit
bit5 :exponent
bit10 :fraction
def sign
sign_bit.zero? ? 1 : -1
end
def get
if exponent == 31 # special value in binary16 - all exponent bits are 1
return fraction.zero? ? (sign * Float::INFINITY) : Float::NAN
end
sign * 2**(exponent - 15) * (1.0 + fraction.to_f / 1024)
end
def set(val)
self.sign = (val >= 0.0)
self.fraction = ... # TODO implement
self.exponent = ... # TODO implement
end
end
I'm trying to do Euler project 13:
Work out the first ten digits of the sum of the following one-hundred 50-digit numbers.
list = [37107287533902102798797998220837590246510135740250,
46376937677490009712648124896970078050417018260538,
74324986199524741059474233309513058123726617309629,
91942213363574161572522430563301811072406154908250,
23067588207539346171171980310421047513778063246676,
89261670696623633820136378418383684178734361726757,
28112879812849979408065481931592621691275889832738,
44274228917432520321923589422876796487670272189318,
47451445736001306439091167216856844588711603153276,
70386486105843025439939619828917593665686757934951,
62176457141856560629502157223196586755079324193331,
64906352462741904929101432445813822663347944758178,
92575867718337217661963751590579239728245598838407,
58203565325359399008402633568948830189458628227828,
80181199384826282014278194139940567587151170094390,
35398664372827112653829987240784473053190104293586,
86515506006295864861532075273371959191420517255829,
71693888707715466499115593487603532921714970056938,
54370070576826684624621495650076471787294438377604,
53282654108756828443191190634694037855217779295145,
36123272525000296071075082563815656710885258350721,
45876576172410976447339110607218265236877223636045,
17423706905851860660448207621209813287860733969412,
81142660418086830619328460811191061556940512689692,
51934325451728388641918047049293215058642563049483,
62467221648435076201727918039944693004732956340691,
15732444386908125794514089057706229429197107928209,
55037687525678773091862540744969844508330393682126,
18336384825330154686196124348767681297534375946515,
80386287592878490201521685554828717201219257766954,
78182833757993103614740356856449095527097864797581,
16726320100436897842553539920931837441497806860984,
48403098129077791799088218795327364475675590848030,
87086987551392711854517078544161852424320693150332,
59959406895756536782107074926966537676326235447210,
69793950679652694742597709739166693763042633987085,
41052684708299085211399427365734116182760315001271,
65378607361501080857009149939512557028198746004375,
35829035317434717326932123578154982629742552737307,
94953759765105305946966067683156574377167401875275,
88902802571733229619176668713819931811048770190271,
25267680276078003013678680992525463401061632866526,
36270218540497705585629946580636237993140746255962,
24074486908231174977792365466257246923322810917141,
91430288197103288597806669760892938638285025333403,
34413065578016127815921815005561868836468420090470,
23053081172816430487623791969842487255036638784583,
11487696932154902810424020138335124462181441773470,
63783299490636259666498587618221225225512486764533,
67720186971698544312419572409913959008952310058822,
95548255300263520781532296796249481641953868218774,
76085327132285723110424803456124867697064507995236,
37774242535411291684276865538926205024910326572967,
23701913275725675285653248258265463092207058596522,
29798860272258331913126375147341994889534765745501,
18495701454879288984856827726077713721403798879715,
38298203783031473527721580348144513491373226651381,
34829543829199918180278916522431027392251122869539,
40957953066405232632538044100059654939159879593635,
29746152185502371307642255121183693803580388584903,
41698116222072977186158236678424689157993532961922,
62467957194401269043877107275048102390895523597457,
23189706772547915061505504953922979530901129967519,
86188088225875314529584099251203829009407770775672,
11306739708304724483816533873502340845647058077308,
82959174767140363198008187129011875491310547126581,
97623331044818386269515456334926366572897563400500,
42846280183517070527831839425882145521227251250327,
55121603546981200581762165212827652751691296897789,
32238195734329339946437501907836945765883352399886,
75506164965184775180738168837861091527357929701337,
62177842752192623401942399639168044983993173312731,
32924185707147349566916674687634660915035914677504,
99518671430235219628894890102423325116913619626622,
73267460800591547471830798392868535206946944540724,
76841822524674417161514036427982273348055556214818,
97142617910342598647204516893989422179826088076852,
87783646182799346313767754307809363333018982642090,
10848802521674670883215120185883543223812876952786,
71329612474782464538636993009049310363619763878039,
62184073572399794223406235393808339651327408011116,
66627891981488087797941876876144230030984490851411,
60661826293682836764744779239180335110989069790714,
85786944089552990653640447425576083659976645795096,
66024396409905389607120198219976047599490197230297,
64913982680032973156037120041377903785566085089252,
16730939319872750275468906903707539413042652315011,
94809377245048795150954100921645863754710598436791,
78639167021187492431995700641917969777599028300699,
15368713711936614952811305876380278410754449733078,
40789923115535562561142322423255033685442488917353,
44889911501440648020369068063960672322193204149535,
41503128880339536053299340368006977710650566631954,
81234880673210146739058568557934581403627822703280,
82616570773948327592232845941706525094512325230608,
22918802058777319719839450180888072429661980811197,
77158542502016545090413245809786882778948721859617,
72107838435069186155435662884062257473692284509516,
20849603980134001723930671666823555245252804609722,
53503534226472524250874054075591789781264330331690]
Here is my code:
def countNumbers(list)
value = 0
(0..list.count).each { |y| value += list[y] }
return value
end
puts "#{countNumbers(list)}"
I get: *nil can't be coerced into Bignum* error when I run the code.
The issue is with the range in countNumbers method.
0..list.count returns 0 to 100 with 100 included but list[100] is nil.
Change it to 0...list.count with return 0 to 99.
See the documentation to better understand using .. and ...
I worked up a working code to check if a credit card is valid using luhn algorithm:
class CreditCard
def initialize(num)
##num_arr = num.to_s.split("")
raise ArgumentError.new("Please enter exactly 16 digits for the credit card number.")
if ##num_arr.length != 16
#num = num
end
def check_card
final_ans = 0
i = 0
while i < ##num_arr.length
(i % 2 == 0) ? ans = (##num_arr[i].to_i * 2) : ans = ##num_arr[i].to_i
if ans > 9
tens = ans / 10
ones = ans % 10
ans = tens + ones
end
final_ans += ans
i += 1
end
final_ans % 10 == 0 ? true : false
end
end
However, when I create driver test codes to check for it, it doesn't work:
card_1 = CreditCard.new(4563960122001999)
card_2 = CreditCard.new(4563960122001991)
p card_1.check_card
p card_2.check_card
I've been playing around with the code, and I noticed that the driver code works if I do this:
card_1 = CreditCard.new(4563960122001999)
p card_1.check_card
card_2 = CreditCard.new(4563960122001991)
p card_2.check_card
I tried to research before posting on why this is happening. Logically, I don't see why the first driver codes wouldn't work. Can someone please assist me as to why this is happening?
Thanks in advance!!!
You are using a class variable that starts with ##, which is shared among all instances of CreditCard as well as the class (and other related classes). Therefore, the value will be overwritten every time you create a new instance or apply check_card to some instance. In your first example, the class variable will hold the result for the last application of the method, and hence will reflect the result for the last instance (card_2).