Finally got this working (thanks, all) with just the following line of code:

use bigint (a => 80);
[download]

I am curious about how to assign Math::BigInt or Math::BigFloat (or bignum or bigint) only for the variables that need it. Can you enlighten me on how to do that?

In that case don't use bignum;, instead use Math::BigInt; and/or use Math::BigFloat;, and then create the objects explicitly, as in my $i = Math::BigInt->new(1);. If you're done with the calculations and don't want them to be objects anymore, you can stringify them, e.g. $i = "$1"; - don't use them as numbers or you'll loose the accuracy.

Is the following returning correct results?

# for https://perlmonks.org/?node_id=11110997
# by bliako, 08/01/2020

use strict;
use warnings;

use Math::BigInt;
use Digest::SHA qw(sha256_hex);

for(my $i=1;$i<=10;$i++){
    # the sha as a hex string (no '0x' prepended)
    my $hexstr = sha256_hex($i);

    # to create a bigint from a hex string we need to prepend '0x' to 
+it
    my $digest = Math::BigInt->new('0x'.$hexstr);
    # specify accuracy and precision
    $digest->accuracy(80);
    $digest->precision(1);
    # operate
    print "$i $digest\n";
    $digest /= 64;
    print "$i $digest\n";
}
[download]

1 48635463943209834798109814161294753926839975257569795305637098542720
+658922320
1 75992912411265366872046584627023053010687461339952805165057966473001
+0295660
2 96094161643976066833367867971426158458230048495430276217795328666133
+331159860
2 15014712756871260442713729370535337259098445077410980659030520104083
+33299370
3 35293215426786447154857697798367884701614677727176325092965345248689
+205321680
3 55145649104353823679465152809949819846272933948713007957758351951076
+8833150
4 33984360982413536682390860969296307922929415152052354251133793603654
+468157320
4 53100564035021151066235720264525481129577211175081803517396552505710
+1064960
5 10818240655469999731486825095773005325907358940236581977057259273658
+4172823450
5 16903501024171874580448164212145320821730248344119659339151967615091
+27700370
6 10492023800686533720501340709024820017001830686534338836405100876796
+5015414400
6 16393787188572708938283344857851281276565360447709904431882970119994
+53365850
7 54734117258892461880478870895348100103198302433611928089023761078319
+507514450
7 85522058217019471688248235773981406411247347552518637639099626684874
+2304910
8 20075373234943686845167158285967784892467090849631486320124245130906
+619831460
8 31367770679599510695573684821824663894479829452549197375194133017041
+5934870
9 11463511883541201508393500803711559652562721115888819482889049505863
+143503290
9 17911737318033127356864845005799311957129251743576280442014139852911
+1617240
10 3359281535163583886622750554468341756416232122807515421831543601247
+6449103320
10 5248877398693099822848047741356783994400362691886742846611786876949
+44517240
[download]

Still, I would like to find out what's going on in that loop and gets stuck to 10 !!!!

bw, bliako

Still, I would like to find out what's going on in that loop and gets stuck to 10 !!!!

Yes - we've glossed over that and we (I, at least) should not have done so.
My (pathetic) excuse is that Math::BigInt is low priority for me.

Can you reproduce the behaviour ?
I can - on Windows 7, perl-5.30.0.

It's the use bignum (p => 1); line that causes the problem.
Change that line to merely use bignum; and that particular problem goes away.

Cheers,
Rob

Is the following returning correct results?

Not exactly (a small loss of precision at the very end of each number). As I noted above, the output (for 1) should consist of:

4863546394320983479810981416129475392683997525756979530563709854272065
+8922315
7599291241126536687204658462702305301068746133995280516505796647300102
+95661
[download]

Still, better than my first attempt. :)