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Usage examples

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David Bürgin edited this page Jul 4, 2016 · 23 revisions

Here are some practical usage examples of magnum.vim.

FizzBuzz

The classic problem implemented with magnum.vim. Note Rem for 'remainder'.

let three = magnum#Int(3)
let five = magnum#Int(5)

for i in range(1, 100)
  let n = magnum#Int(i)
  if n.Rem(three).IsZero() && n.Rem(five).IsZero()
    echo "FizzBuzz"
  elseif n.Rem(three).IsZero()
    echo "Fizz"
  elseif n.Rem(five).IsZero()
    echo "Buzz"
  else
    echo n.Number()
  endif
endfor

Average voting time

Given some UNIX timestamps, determine the average. This is something you can't do with Vim numbers. (Or couldn't: Vim version 7.4.1976 has added support for 64-bit integers when the feature +num64 is enabled.)

let times = [
  \ 1390938148,
  \ 1390759759,
  \ 1391028429,
  \ 1390992724,
  \ 1391100465,
  \ ]

let sum = magnum#ZERO
for time in times
  let sum = sum.Add(magnum#Int(time))
endfor
let tally = magnum#Int(len(times))
let average = sum.Div(tally).Number()

Prevent number overflow

You can use this library to prevent integer overflow.

let userinput = input("Please enter a number: ")
let int = magnum#Int(userinput)

try
  let n = int.Number()
catch /^magnum:/
  echo "The number you entered is too big!"
endtry

Integer.Number throws an exception when the Integer value doesn't fit in a Vim number.

Base conversion

The constructor magnum#Int and the accessor String both take an optional argument in the range from 2 to 36 to specify the base to be used. These are safer and more powerful than the built-in str2nr and printf:

echo    magnum#Int('9876543210').String()   str2nr('9876543210')
echo    magnum#Int('base-16?!', 16)         str2nr('base-16?!', 16)
echo    magnum#Int(-0x21d).String(16)       printf('%x', -0x21d)
echo    magnum#Int(74621).String(2)

" (1)   '9876543210'                        '1286608618'
" (2)   throws exception                    '186'
" (3)   '-21d'                              'fffffde3'
" (4)   '10010001101111101'

Random 64-bit UID

magnum#random#NextInt is a simple but effective random number generator. For example, enter the command :echo magnum#random#NextInt(magnum#Int(6)).Add(magnum#ONE).Number() to simulate one die roll.

Here is a more practical example. In Java, Serializable classes should generally have a field static final long serialVersionUID that holds a 64-bit signed integer ID.

I like to use a mapping to insert a random long after the cursor exactly for this purpose:

let two63 = magnum#Int(2).Pow(63)
nnoremap <Leader>rl "=magnum#random#NextInt(two63.Neg(), two63).String()<CR>p

Euler problem 13

Solution to Euler problem 13, 'Large sum': Produce the first ten digits of a large sum.

let numbers = '
\ 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'

let result = magnum#ZERO
for n in map(split(numbers), 'magnum#Int(v:val)')
  let result = result.Add(n)
endfor
echo result.String()[0:9]

Echoes 5537376230.

Testing for zero

In descending order of sanity.

let void = value.IsZero()

let void = value.Eq(magnum#ZERO)
let void = value.Cmp(magnum#ZERO) == 0
let void = value.Eq(magnum#Int('0'))
let void = str2nr(value.String(16), 16) == eval('0x0')

Only bad ideas here. Don't ever use anything except the first.

Pronounceable Git commit hashes

I'm not getting desperate here. This is interesting.

let hash = 'b909f0e074b40c5e543c6409f0eb768d7ff00fb5'
let n = magnum#Int(hash, 16)
let word = substitute(n.String(36), '[0-9qv-z]', '', 'g')[:7]
echo word

Echoes lmireppo.

Euclidean division and modulus

For an example of how to extend the capabilities of magnum.vim check out the example given over here.

let a = magnum#Int(-13)
let b = magnum#Int(4)
echo map(a.DivRem(b), 'v:val.Number()')
" [-3, -1]
echo map(DivMod(a, b), 'v:val.Number()')
" [-4, 3]

That's all for today, thank you for reading.

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