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| − | =In-place vs. Copy Modification=
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| − | Whether Math::BigInt does its thing in-place or not depends on whether you use the methods or the overloaded operators.
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| − | ==Methods Work In-Place==
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| − | If you use the methods, modification is in-place, regardless of context. A new object is not created for a result.
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| − | <nowiki>
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| − | use Math::BigInt;
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| − |
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| − | # Apparently part of this program got lost.
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| − | # Will try to find it later. -- PSM
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| − |
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| − | bless $_[1], $pb;
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| − | bless $_[0], $pa;
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| − | $v;
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| − | }
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| − |
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| − | # Void context
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| − | my $a = new Math::BigInt '27';
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| − | $a->badd(3);
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| − | $a == '30'
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| − | or die "a=$a";
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| − |
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| − | # Scalar context
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| − | my $b = new Math::BigInt '27';
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| − | my $c = $b->badd(3);
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| − | $b == '30'
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| − | or die "b=$b";
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| − | same_object($b,$c)
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| − | or die "b and c are not the same object";
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| − | </nowiki>
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| − |
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| − | ==Overloads Use Copies==
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| − | Meanwhile, overloaded operators treat the objects like regular scalars; nothing is modified in place unless an assignment operator (including <code>+=</code>, <code>*=</code>, ''etc.'', but not <code>=</code> for Perl reasons) is used.
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| − | # Void context using overloads
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| − | # does not work in-place
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| − | my $d = new Math::BigInt '57';
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| − | $d + 3;
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| − | $d == '57'
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| − | or die "d=$d";
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| − |
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| − | # Scalar context using overloads
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| − | # does not work in-place
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| − | my $e = new Math::BigInt '97';
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| − | my $f = $e + 4;
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| − | $e == '97'
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| − | or die "e=$e";
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| − | $f == '101'
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| − | or die "f=$f";
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| − |
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| − | =Converting a binary string to a BigInt=
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| − | This code conveniently reinterprets raw bytes as [[hexadecimals|hexadecimal]] digits, big-endian style, so that the data may be cast into a bigint. This code doesn't do any buffering; for that, try my new Xana::Math::RawDataUtil module in [[Xana]].
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| − | # Unsigned
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| − | my $a = "ZYXWVUT";
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| − | my $ba = new Math::BigInt '0x' . unpack('H*',$a);
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| − | # Test
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| − | $ba == '25430983861228884'
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| − | or die "ba=$ba";
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| − |
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| − | # Signed
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| − | sub raw_to_signed_bigint ($) {
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| − | # The MSB is the sign bit.
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| − | if(unpack('C',substr($_[0],0,1)) & 0x80) {
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| − | my $hex = unpack('H*',$_[0]);
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| − | # Invert the hex digits.
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| − | $hex =~ tr/0123456789aAbBcCdDeEfF/fedcba9876554433221100/;
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| − | my $bigint = new Math::BigInt "0x$hex";
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| − | # Then, the ones complement is the right answer.
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| − | return $bigint->bnot();
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| − | } else {
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| − | # The normal unsigned thing.
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| − | return Math::BigInt->new( '0x' . unpack('H*',$_[0]) );
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| − | }
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| − | }
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| − |
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| − | # Tests
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| − | my $bb = raw_to_signed_bigint "\xFF\x54\xAB\x56\x73\x14\xE0\xF5\x2E";
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| − | $bb == '-12345678901234567890'
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| − | or die "bb=$bb";
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| − |
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| − | my $bc = raw_to_signed_bigint "\xFF";
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| − | $bc == '-1'
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| − | or die "bc=$bc";
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| − |
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| − | my $bd = raw_to_signed_bigint "ZYXWVUT";
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| − | $bd == '25430983861228884'
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| − | or die "bd=$bd";
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| − |
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| − | =See Also=
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| − |
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| − | * [http://search.cpan.org/~tels/Math-BigInt-1.75/lib/Math/BigInt.pm CPAN]
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