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lib/Math/BigInt/LTM.pm  view on Meta::CPAN

    return $n;
}

### same as _sadd() in Math::BigInt::Lib
# Signed addition. If the flag is false, $xa might be modified, but not $ya. If
# the false is true, $ya might be modified, but not $xa.
sub _sadd {
    my $class = shift;
    my ($xa, $xs, $ya, $ys, $flag) = @_;
    my ($za, $zs);

    # If the signs are equal we can add them (-5 + -3 => -(5 + 3) => -8)

    if ($xs eq $ys) {
        if ($flag) {
            $za = $class -> _add($ya, $xa);
        } else {
            $za = $class -> _add($xa, $ya);
        }
        $zs = $class -> _is_zero($za) ? '+' : $xs;
        return $za, $zs;
    }

    my $acmp = $class -> _acmp($xa, $ya);       # abs(x) = abs(y)

    if ($acmp == 0) {                           # x = -y or -x = y
        $za = $class -> _zero();
        $zs = '+';
        return $za, $zs;
    }

    if ($acmp > 0) {                            # abs(x) > abs(y)
        $za = $class -> _sub($xa, $ya, $flag);
        $zs = $xs;
    } else {                                    # abs(x) < abs(y)
        $za = $class -> _sub($ya, $xa, !$flag);
        $zs = $ys;
    }
    return $za, $zs;
}

### same as _ssub() in Math::BigInt::Lib
# Signed subtraction. If the flag is false, $xa might be modified, but not $ya.
# If the false is true, $ya might be modified, but not $xa.
sub _ssub {
    my $class = shift;
    my ($xa, $xs, $ya, $ys, $flag) = @_;

    # Swap sign of second operand and let _sadd() do the job.
    $ys = $ys eq '+' ? '-' : '+';
    $class -> _sadd($xa, $xs, $ya, $ys, $flag);
}

### same as _log_int() in Math::BigInt::Lib
sub _log_int {
    # calculate integer log of $x to base $base
    # ref to array, ref to array - return ref to array
    my ($class, $x, $base) = @_;

    # X == 0 => NaN
    return if $class -> _is_zero($x);

    $base = $class -> _new(2)     unless defined($base);
    $base = $class -> _new($base) unless ref($base);

    # BASE 0 or 1 => NaN
    return if $class -> _is_zero($base) || $class -> _is_one($base);

    # X == 1 => 0 (is exact)
    if ($class -> _is_one($x)) {
        return $class -> _zero(), 1;
    }

    my $cmp = $class -> _acmp($x, $base);

    # X == BASE => 1 (is exact)
    if ($cmp == 0) {
        return $class -> _one(), 1;
    }

    # 1 < X < BASE => 0 (is truncated)
    if ($cmp < 0) {
        return $class -> _zero(), 0;
    }

    my $y;

    # log(x) / log(b) = log(xm * 10^xe) / log(bm * 10^be)
    #                 = (log(xm) + xe*(log(10))) / (log(bm) + be*log(10))

    {
        my $x_str = $class -> _str($x);
        my $b_str = $class -> _str($base);
        my $xm    = "." . $x_str;
        my $bm    = "." . $b_str;
        my $xe    = length($x_str);
        my $be    = length($b_str);
        my $log10 = log(10);
        my $guess = int((log($xm) + $xe * $log10) / (log($bm) + $be * $log10));
        $y = $class -> _new($guess);
    }

    my $trial = $class -> _pow($class -> _copy($base), $y);
    my $acmp  = $class -> _acmp($trial, $x);

    # Did we get the exact result?

    return $y, 1 if $acmp == 0;

    # Too small?

    while ($acmp < 0) {
        $trial = $class -> _mul($trial, $base);
        $y     = $class -> _inc($y);
        $acmp  = $class -> _acmp($trial, $x);
    }

    # Too big?

    while ($acmp > 0) {
        $trial = $class -> _div($trial, $base);
        $y     = $class -> _dec($y);
        $acmp  = $class -> _acmp($trial, $x);
    }

    return $y, 1 if $acmp == 0;         # result is exact