628 lines
23 KiB
Perl
628 lines
23 KiB
Perl
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#------------------------------------------------------------------------------
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# File: Shift.pl
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#
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# Description: ExifTool time shifting routines
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#
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# Revisions: 10/28/2005 - P. Harvey Created
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#------------------------------------------------------------------------------
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package Image::ExifTool;
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use strict;
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sub ShiftTime($$;$$);
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#------------------------------------------------------------------------------
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# apply shift to value in new value hash
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# Inputs: 0) ExifTool ref, 1) shift type, 2) shift string, 3) raw date/time value,
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# 4) new value hash ref
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# Returns: error string or undef on success and updates value in new value hash
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sub ApplyShift($$$$;$)
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{
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my ($self, $func, $shift, $val, $nvHash) = @_;
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# get shift direction from first character in shift string
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my $pre = ($shift =~ s/^(\+|-)//) ? $1 : '+';
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my $dir = ($pre eq '+') ? 1 : -1;
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my $tagInfo = $$nvHash{TagInfo};
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my $tag = $$tagInfo{Name};
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my $shiftOffset;
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if ($$nvHash{ShiftOffset}) {
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$shiftOffset = $$nvHash{ShiftOffset};
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} else {
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$shiftOffset = $$nvHash{ShiftOffset} = { };
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}
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# initialize handler for eval warnings
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local $SIG{'__WARN__'} = \&SetWarning;
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SetWarning(undef);
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# shift is applied to ValueConv value, so we must ValueConv-Shift-ValueConvInv
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my ($type, $err);
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foreach $type ('ValueConv','Shift','ValueConvInv') {
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if ($type eq 'Shift') {
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#### eval ShiftXxx function
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$err = eval "Shift$func(\$val, \$shift, \$dir, \$shiftOffset)";
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} elsif ($$tagInfo{$type}) {
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my $conv = $$tagInfo{$type};
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if (ref $conv eq 'CODE') {
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$val = &$conv($val, $self);
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} else {
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return "Can't handle $type for $tag in ApplyShift()" if ref $$tagInfo{$type};
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#### eval ValueConv/ValueConvInv ($val, $self)
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$val = eval $$tagInfo{$type};
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}
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} else {
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next;
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}
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# handle errors
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$err and return $err;
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$@ and SetWarning($@);
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GetWarning() and return CleanWarning();
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}
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# update value in new value hash
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$nvHash->{Value} = [ $val ];
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return undef; # success
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}
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#------------------------------------------------------------------------------
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# Check date/time shift
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# Inputs: 0) shift type, 1) shift string (without sign)
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# Returns: updated shift string, or undef on error (and may update shift)
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sub CheckShift($$)
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{
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my ($type, $shift) = @_;
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my $err;
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if ($type eq 'Time') {
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return "No shift direction" unless $shift =~ s/^(\+|-)//;
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# do a test shift to validate the shift string
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my $testTime = '2005:11:02 09:00:13.25-04:00';
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$err = ShiftTime($testTime, $shift, $1 eq '+' ? 1 : -1);
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} else {
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$err = "Unknown shift type ($type)";
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}
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return $err;
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}
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#------------------------------------------------------------------------------
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# return the number of days in a month
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# Inputs: 0) month number (Jan=1, may be outside range), 1) year
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# Returns: number of days in month
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sub DaysInMonth($$)
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{
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my ($mon, $year) = @_;
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my @days = (31,28,31,30,31,30,31,31,30,31,30,31);
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# adjust to the range [0,11]
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while ($mon < 1) { $mon += 12; --$year; }
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while ($mon > 12) { $mon -= 12; ++$year; }
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# return standard number of days unless february on a leap year
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return $days[$mon-1] unless $mon == 2 and not $year % 4;
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# leap years don't occur on even centuries except every 400 years
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return 29 if $year % 100 or not $year % 400;
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return 28;
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}
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#------------------------------------------------------------------------------
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# split times into corresponding components: YYYY mm dd HH MM SS tzh tzm
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# Inputs: 0) date/time or shift string 1) reference to list for returned components
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# 2) optional reference to list of time components (if shift string)
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# Returns: true on success
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# Returned components are 0-Y, 1-M, 2-D, 3-hr, 4-min, 5-sec, 6-tzhr, 7-tzmin
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sub SplitTime($$;$)
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{
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my ($val, $vals, $time) = @_;
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# insert zeros if missing in shift string
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if ($time) {
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$val =~ s/(^|[-+:\s]):/${1}0:/g;
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$val =~ s/:([:\s]|$)/:0$1/g;
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}
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# change dashes to colons in date (for XMP dates)
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if ($val =~ s/^(\d{4})-(\d{2})-(\d{2})/$1:$2:$3/) {
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$val =~ tr/T/ /; # change 'T' separator to ' '
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}
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# add space before timezone to split it into a separate word
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$val =~ s/(\+|-)/ $1/;
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my @words = split ' ', $val;
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my $err = 1;
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my @v;
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for (;;) {
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my $word = shift @words;
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last unless defined $word;
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# split word into separate numbers (allow decimal points but no signs)
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my @vals = $word =~ /(?=\d|\.\d)\d*(?:\.\d*)?/g or last;
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if ($word =~ /^(\+|-)/) {
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# this is the timezone
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(defined $v[6] or @vals > 2) and $err = 1, last;
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my $sign = ($1 ne '-') ? 1 : -1;
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# apply sign to both minutes and seconds
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$v[6] = $sign * shift(@vals);
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$v[7] = $sign * (shift(@vals) || 0);
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} elsif ((@words and $words[0] =~ /^\d+/) or # there is a time word to follow
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(not $time and $vals[0] =~ /^\d{3}/) or # first value is year (3 or more digits)
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($time and not defined $$time[3] and not defined $v[0])) # we don't have a time
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{
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# this is a date (must come first)
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(@v or @vals > 3) and $err = 1, last;
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not $time and @vals != 3 and $err = 1, last;
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$v[2] = pop(@vals); # take day first if only one specified
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$v[1] = pop(@vals) || 0;
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$v[0] = pop(@vals) || 0;
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} else {
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# this is a time (can't come after timezone)
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(defined $v[3] or defined $v[6] or @vals > 3) and $err = 1, last;
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not $time and @vals != 3 and @vals != 2 and $err = 1, last;
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$v[3] = shift(@vals); # take hour first if only one specified
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$v[4] = shift(@vals) || 0;
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$v[5] = shift(@vals) || 0;
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}
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$err = 0;
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}
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return 0 if $err or not @v;
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if ($time) {
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# zero any required shift entries which aren't yet defined
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$v[0] = $v[1] = $v[2] = 0 if defined $$time[0] and not defined $v[0];
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$v[3] = $v[4] = $v[5] = 0 if defined $$time[3] and not defined $v[3];
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$v[6] = $v[7] = 0 if defined $$time[6] and not defined $v[6];
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}
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@$vals = @v; # return split time components
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return 1;
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}
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#------------------------------------------------------------------------------
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# shift date/time by components
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# Inputs: 0) split date/time list ref, 1) split shift list ref,
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# 2) shift direction, 3) reference to output list of shifted components
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# 4) number of decimal points in seconds
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# 5) reference to return time difference due to rounding
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# Returns: error string or undef on success
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sub ShiftComponents($$$$$;$)
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{
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my ($time, $shift, $dir, $toTime, $dec, $rndPt) = @_;
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# min/max for Y, M, D, h, m, s
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my @min = ( 0, 1, 1, 0, 0, 0);
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my @max = (10000,12,28,24,60,60);
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my $i;
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#
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# apply the shift
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#
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my $c = 0;
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for ($i=0; $i<@$time; ++$i) {
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my $v = ($$time[$i] || 0) + $dir * ($$shift[$i] || 0) + $c;
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# handle fractional values by propagating remainders downwards
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if ($v != int($v) and $i < 5) {
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my $iv = int($v);
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$c = ($v - $iv) * $max[$i+1];
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$v = $iv;
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} else {
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$c = 0;
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}
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$$toTime[$i] = $v;
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}
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# round off seconds to the required number of decimal points
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my $sec = $$toTime[5];
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if (defined $sec and $sec != int($sec)) {
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my $mult = 10 ** $dec;
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my $rndSec = int($sec * $mult + 0.5 * ($sec <=> 0)) / $mult;
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$rndPt and $$rndPt = $sec - $rndSec;
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$$toTime[5] = $rndSec;
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}
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#
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# handle overflows, starting with least significant number first (seconds)
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#
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$c = 0;
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for ($i=5; $i>=0; $i--) {
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defined $$time[$i] or $c = 0, next;
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# apply shift and adjust for previous overflow
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my $v = $$toTime[$i] + $c;
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$c = 0; # set carry to zero
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# adjust for over/underflow
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my ($min, $max) = ($min[$i], $max[$i]);
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if ($v < $min) {
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if ($i == 2) { # 2 = day of month
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do {
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# add number of days in previous month
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--$c;
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my $mon = $$toTime[$i-1] + $c;
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$v += DaysInMonth($mon, $$toTime[$i-2]);
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} while ($v < 1);
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} else {
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my $fc = ($v - $min) / $max;
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# carry ($c) must be largest integer equal to or less than $fc
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$c = int($fc);
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--$c if $c > $fc;
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$v -= $c * $max;
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}
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} elsif ($v >= $max + $min) {
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if ($i == 2) {
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for (;;) {
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# test against number of days in current month
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my $mon = $$toTime[$i-1] + $c;
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my $days = DaysInMonth($mon, $$toTime[$i-2]);
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last if $v <= $days;
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$v -= $days;
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++$c;
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last if $v <= 28;
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}
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} else {
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my $fc = ($v - $max - $min) / $max;
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# carry ($c) must be smallest integer greater than $fc
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$c = int($fc);
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++$c if $c <= $fc;
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$v -= $c * $max;
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}
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}
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$$toTime[$i] = $v; # save the new value
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}
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# handle overflows in timezone
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if (defined $$toTime[6]) {
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my $m = $$toTime[6] * 60 + $$toTime[7];
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$m += 0.5 * ($m <=> 0); # avoid round-off errors
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$$toTime[6] = int($m / 60);
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$$toTime[7] = int($m - $$toTime[6] * 60);
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}
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return undef; # success
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}
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#------------------------------------------------------------------------------
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# Shift an integer or floating-point number
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# Inputs: 0) date/time string, 1) shift string, 2) shift direction (+1 or -1)
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# 3) (unused)
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# Returns: undef and updates input value
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sub ShiftNumber($$$;$)
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{
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my ($val, $shift, $dir) = @_;
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$_[0] = $val + $shift * $dir; # return shifted value
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return undef; # success!
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}
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#------------------------------------------------------------------------------
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# Shift date/time string
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# Inputs: 0) date/time string, 1) shift string, 2) shift direction (+1 or -1),
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# or 0 or undef to take shift direction from sign of shift,
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# 3) reference to ShiftOffset hash (with Date, DateTime, Time, Timezone keys)
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# Returns: error string or undef on success and date/time string is updated
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sub ShiftTime($$;$$)
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{
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local $_;
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my ($val, $shift, $dir, $shiftOffset) = @_;
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my (@time, @shift, @toTime, $mode, $needShiftOffset, $dec);
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$dir or $dir = ($shift =~ s/^(\+|-)// and $1 eq '-') ? -1 : 1;
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#
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# figure out what we are dealing with (time, date or date/time)
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#
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SplitTime($val, \@time) or return "Invalid time string ($val)";
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if (defined $time[0]) {
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$mode = defined $time[3] ? 'DateTime' : 'Date';
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} elsif (defined $time[3]) {
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$mode = 'Time';
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}
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# get number of digits after the seconds decimal point
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if (defined $time[5] and $time[5] =~ /\.(\d+)/) {
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$dec = length($1);
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} else {
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$dec = 0;
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}
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if ($shiftOffset) {
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$needShiftOffset = 1 unless defined $$shiftOffset{$mode};
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$needShiftOffset = 1 if defined $time[6] and not defined $$shiftOffset{Timezone};
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} else {
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$needShiftOffset = 1;
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}
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if ($needShiftOffset) {
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#
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# apply date/time shift the hard way
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#
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SplitTime($shift, \@shift, \@time) or return "Invalid shift string ($shift)";
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# change 'Z' timezone to '+00:00' only if necessary
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if (@shift > 6 and @time <= 6) {
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$time[6] = $time[7] = 0 if $val =~ s/Z$/\+00:00/;
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}
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my $rndDiff;
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my $err = ShiftComponents(\@time, \@shift, $dir, \@toTime, $dec, \$rndDiff);
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$err and return $err;
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#
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# calculate and save the shift offsets for next time
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#
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if ($shiftOffset) {
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if (defined $time[0] or defined $time[3]) {
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my @tm1 = (0, 0, 0, 1, 0, 2000);
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my @tm2 = (0, 0, 0, 1, 0, 2000);
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if (defined $time[0]) {
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@tm1[3..5] = reverse @time[0..2];
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@tm2[3..5] = reverse @toTime[0..2];
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--$tm1[4]; # month should start from 0
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--$tm2[4];
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}
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my $diff = 0;
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if (defined $time[3]) {
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@tm1[0..2] = reverse @time[3..5];
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@tm2[0..2] = reverse @toTime[3..5];
|
||
|
|
# handle fractional seconds separately
|
||
|
|
$diff = $tm2[0] - int($tm2[0]) - ($tm1[0] - int($tm1[0]));
|
||
|
|
$diff += $rndDiff if defined $rndDiff; # un-do rounding
|
||
|
|
$tm1[0] = int($tm1[0]);
|
||
|
|
$tm2[0] = int($tm2[0]);
|
||
|
|
}
|
||
|
|
eval q{
|
||
|
|
require Time::Local;
|
||
|
|
$diff += Time::Local::timegm(@tm2) - Time::Local::timegm(@tm1);
|
||
|
|
};
|
||
|
|
# not a problem if we failed here since we'll just try again next time,
|
||
|
|
# so don't return error message
|
||
|
|
unless (@$) {
|
||
|
|
my $mode;
|
||
|
|
if (defined $time[0]) {
|
||
|
|
$mode = defined $time[3] ? 'DateTime' : 'Date';
|
||
|
|
} else {
|
||
|
|
$mode = 'Time';
|
||
|
|
}
|
||
|
|
$$shiftOffset{$mode} = $diff;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
if (defined $time[6]) {
|
||
|
|
$$shiftOffset{Timezone} = ($toTime[6] - $time[6]) * 60 +
|
||
|
|
$toTime[7] - $time[7];
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
} else {
|
||
|
|
#
|
||
|
|
# apply shift from previously calculated offsets
|
||
|
|
#
|
||
|
|
if ($$shiftOffset{Timezone} and @time <= 6) {
|
||
|
|
# change 'Z' timezone to '+00:00' only if necessary
|
||
|
|
$time[6] = $time[7] = 0 if $val =~ s/Z$/\+00:00/;
|
||
|
|
}
|
||
|
|
# apply the previous date/time shift if necessary
|
||
|
|
if ($mode) {
|
||
|
|
my @tm = (0, 0, 0, 1, 0, 2000);
|
||
|
|
if (defined $time[0]) {
|
||
|
|
@tm[3..5] = reverse @time[0..2];
|
||
|
|
--$tm[4]; # month should start from 0
|
||
|
|
}
|
||
|
|
@tm[0..2] = reverse @time[3..5] if defined $time[3];
|
||
|
|
# save fractional seconds
|
||
|
|
my $frac = $tm[0] - int($tm[0]);
|
||
|
|
$tm[0] = int($tm[0]);
|
||
|
|
my $tm;
|
||
|
|
eval q{
|
||
|
|
require Time::Local;
|
||
|
|
$tm = Time::Local::timegm(@tm) + $frac;
|
||
|
|
};
|
||
|
|
$@ and return CleanWarning($@);
|
||
|
|
$tm += $$shiftOffset{$mode}; # apply the shift
|
||
|
|
$tm < 0 and return 'Shift results in negative time';
|
||
|
|
# save fractional seconds in shifted time
|
||
|
|
$frac = $tm - int($tm);
|
||
|
|
if ($frac) {
|
||
|
|
$tm = int($tm);
|
||
|
|
# must account for any rounding that could occur
|
||
|
|
$frac + 0.5 * 10 ** (-$dec) >= 1 and ++$tm, $frac = 0;
|
||
|
|
}
|
||
|
|
@tm = gmtime($tm);
|
||
|
|
@toTime = reverse @tm[0..5];
|
||
|
|
$toTime[0] += 1900;
|
||
|
|
++$toTime[1];
|
||
|
|
$toTime[5] += $frac; # add the fractional seconds back in
|
||
|
|
}
|
||
|
|
# apply the previous timezone shift if necessary
|
||
|
|
if (defined $time[6]) {
|
||
|
|
my $m = $time[6] * 60 + $time[7];
|
||
|
|
$m += $$shiftOffset{Timezone};
|
||
|
|
$m += 0.5 * ($m <=> 0); # avoid round-off errors
|
||
|
|
$toTime[6] = int($m / 60);
|
||
|
|
$toTime[7] = int($m - $toTime[6] * 60);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
#
|
||
|
|
# insert shifted time components back into original string
|
||
|
|
#
|
||
|
|
my ($i, $err);
|
||
|
|
for ($i=0; $i<@toTime; ++$i) {
|
||
|
|
next unless defined $time[$i] and defined $toTime[$i];
|
||
|
|
my ($v, $d, $s);
|
||
|
|
if ($i != 6) { # not timezone hours
|
||
|
|
last unless $val =~ /((?=\d|\.\d)\d*(\.\d*)?)/g;
|
||
|
|
next if $toTime[$i] == $time[$i];
|
||
|
|
$v = $1; # value
|
||
|
|
$d = $2; # decimal part of value
|
||
|
|
$s = ''; # no sign
|
||
|
|
} else {
|
||
|
|
last if $time[$i] == $toTime[$i] and $time[$i+1] == $toTime[$i+1];
|
||
|
|
last unless $val =~ /((?:\+|-)(?=\d|\.\d)\d*(\.\d*)?)/g;
|
||
|
|
$v = $1;
|
||
|
|
$d = $2;
|
||
|
|
if ($toTime[6] >= 0 and $toTime[7] >= 0) {
|
||
|
|
$s = '+';
|
||
|
|
} else {
|
||
|
|
$s = '-';
|
||
|
|
$toTime[6] = -$toTime[6];
|
||
|
|
$toTime[7] = -$toTime[7];
|
||
|
|
}
|
||
|
|
}
|
||
|
|
my $nv = $toTime[$i];
|
||
|
|
my $pos = pos $val;
|
||
|
|
my $len = length $v;
|
||
|
|
my $sig = $len - length $s;
|
||
|
|
my $dec = $d ? length($d) - 1 : 0;
|
||
|
|
my $newNum = sprintf($dec ? "$s%0$sig.${dec}f" : "$s%0${sig}d", $nv);
|
||
|
|
length($newNum) != $len and $err = 1;
|
||
|
|
substr($val, $pos - $len, $len) = $newNum;
|
||
|
|
pos($val) = $pos;
|
||
|
|
}
|
||
|
|
$err and return "Error packing shifted time ($val)";
|
||
|
|
$_[0] = $val; # return shifted value
|
||
|
|
return undef; # success!
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
1; # end
|
||
|
|
|
||
|
|
__END__
|
||
|
|
|
||
|
|
=head1 NAME
|
||
|
|
|
||
|
|
Image::ExifTool::Shift.pl - ExifTool time shifting routines
|
||
|
|
|
||
|
|
=head1 DESCRIPTION
|
||
|
|
|
||
|
|
This module contains routines used by ExifTool to shift date and time
|
||
|
|
values.
|
||
|
|
|
||
|
|
=head1 METHODS
|
||
|
|
|
||
|
|
=head2 ShiftTime
|
||
|
|
|
||
|
|
Shift date/time value
|
||
|
|
|
||
|
|
use Image::ExifTool;
|
||
|
|
$err = Image::ExifTool::ShiftTime($dateTime, $shift);
|
||
|
|
|
||
|
|
=over 4
|
||
|
|
|
||
|
|
=item Inputs:
|
||
|
|
|
||
|
|
0) Date/time string in EXIF format (eg. C<2016:01:30 11:45:00>).
|
||
|
|
|
||
|
|
1) Shift string (see below) with optional leading sign for shift direction.
|
||
|
|
|
||
|
|
2) [optional] Direction of shift (-1 or +1), or 0 or undef to use the sign
|
||
|
|
from the shift string.
|
||
|
|
|
||
|
|
3) [optional] Reference to time-shift hash -- filled in by first call to
|
||
|
|
B<ShiftTime>, and used in subsequent calls to shift date/time values by the
|
||
|
|
same relative amount (see L</TRICKY> section below).
|
||
|
|
|
||
|
|
=item Return value:
|
||
|
|
|
||
|
|
Error string, or undef on success and the input date/time string is shifted
|
||
|
|
by the specified amount.
|
||
|
|
|
||
|
|
=back
|
||
|
|
|
||
|
|
=head1 SHIFT STRING
|
||
|
|
|
||
|
|
Time shifts are applied to standard EXIF-formatted date/time values (eg.
|
||
|
|
C<2005:03:14 18:55:00>). Date-only and time-only values may also be
|
||
|
|
shifted, and an optional timezone (eg. C<-05:00>) is also supported. Here
|
||
|
|
are some general rules and examples to explain how shift strings are
|
||
|
|
interpreted:
|
||
|
|
|
||
|
|
Date-only values are shifted using the following formats:
|
||
|
|
|
||
|
|
'Y:M:D' - shift date by 'Y' years, 'M' months and 'D' days
|
||
|
|
'M:D' - shift months and days only
|
||
|
|
'D' - shift specified number of days
|
||
|
|
|
||
|
|
Time-only values are shifted using the following formats:
|
||
|
|
|
||
|
|
'h:m:s' - shift time by 'h' hours, 'm' minutes and 's' seconds
|
||
|
|
'h:m' - shift hours and minutes only
|
||
|
|
'h' - shift specified number of hours
|
||
|
|
|
||
|
|
Timezone shifts are specified in the following formats:
|
||
|
|
|
||
|
|
'+h:m' - shift timezone by 'h' hours and 'm' minutes
|
||
|
|
'-h:m' - negative shift of timezone hours and minutes
|
||
|
|
'+h' - shift timezone hours only
|
||
|
|
'-h' - negative shift of timezone hours only
|
||
|
|
|
||
|
|
A valid shift value consists of one or two arguments, separated by a space.
|
||
|
|
If only one is provided, it is assumed to be a time shift when applied to a
|
||
|
|
time-only or a date/time value, or a date shift when applied to a date-only
|
||
|
|
value. For example:
|
||
|
|
|
||
|
|
'1' - shift by 1 hour if applied to a time or date/time
|
||
|
|
value, or by one day if applied to a date value
|
||
|
|
'2:0' - shift 2 hours (time, date/time), or 2 months (date)
|
||
|
|
'5:0:0' - shift 5 hours (time, date/time), or 5 years (date)
|
||
|
|
'0:0:1' - shift 1 s (time, date/time), or 1 day (date)
|
||
|
|
|
||
|
|
If two arguments are given, the date shift is first, followed by the time
|
||
|
|
shift:
|
||
|
|
|
||
|
|
'3:0:0 0' - shift date by 3 years
|
||
|
|
'0 15:30' - shift time by 15 hours and 30 minutes
|
||
|
|
'1:0:0 0:0:0+5:0' - shift date by 1 year and timezone by 5 hours
|
||
|
|
|
||
|
|
A date shift is simply ignored if applied to a time value or visa versa.
|
||
|
|
|
||
|
|
Numbers specified in shift fields may contain a decimal point:
|
||
|
|
|
||
|
|
'1.5' - 1 hour 30 minutes (time, date/time), or 1 day (date)
|
||
|
|
'2.5 0' - 2 days 12 hours (date/time), 12 hours (time) or
|
||
|
|
2 days (date)
|
||
|
|
|
||
|
|
And to save typing, a zero is assumed for any missing numbers:
|
||
|
|
|
||
|
|
'1::' - shift by 1 hour (time, date/time) or 1 year (date)
|
||
|
|
'26:: 0' - shift date by 26 years
|
||
|
|
'+:30' - shift timezone by 30 minutes
|
||
|
|
|
||
|
|
Below are some specific examples applied to real date and/or time values
|
||
|
|
('Dir' is the applied shift direction: '+' is positive, '-' is negative):
|
||
|
|
|
||
|
|
Original Value Shift Dir Shifted Value
|
||
|
|
--------------------- ------- --- ---------------------
|
||
|
|
'20:30:00' '5' + '01:30:00'
|
||
|
|
'2005:01:27' '5' + '2005:02:01'
|
||
|
|
'2005:01:27 20:30:00' '5' + '2005:01:28 01:30:00'
|
||
|
|
'11:54:00' '2.5 0' - '23:54:00'
|
||
|
|
'2005:11:02' '2.5 0' - '2005:10:31'
|
||
|
|
'2005:11:02 11:54:00' '2.5 0' - '2005:10:30 23:54:00'
|
||
|
|
'2004:02:28 08:00:00' '1 1.3' + '2004:02:29 09:18:00'
|
||
|
|
'07:00:00' '-5' + '07:00:00'
|
||
|
|
'07:00:00+01:00' '-5' + '07:00:00-04:00'
|
||
|
|
'07:00:00Z' '+2:30' - '07:00:00-02:30'
|
||
|
|
'1970:01:01' '35::' + '2005:01:01'
|
||
|
|
'2005:01:01' '400' + '2006:02:05'
|
||
|
|
'10:00:00.00' '::1.33' - '09:59:58.67'
|
||
|
|
|
||
|
|
=head1 NOTES
|
||
|
|
|
||
|
|
The format of the original date/time value is not changed when the time
|
||
|
|
shift is applied. This means that the length of the date/time string will
|
||
|
|
not change, and only the numbers in the string will be modified. The only
|
||
|
|
exception to this rule is that a 'Z' timezone is changed to '+00:00'
|
||
|
|
notation if a timezone shift is applied. A timezone will not be added to
|
||
|
|
the date/time string.
|
||
|
|
|
||
|
|
=head1 TRICKY
|
||
|
|
|
||
|
|
This module is perhaps more complicated than it needs to be because it is
|
||
|
|
designed to be very flexible in the way time shifts are specified and
|
||
|
|
applied...
|
||
|
|
|
||
|
|
The ability to shift dates by Y years, M months, etc, conflicts with the
|
||
|
|
design goal of maintaining a constant shift for all time values when
|
||
|
|
applying a batch shift. This is because shifting by 1 month can be
|
||
|
|
equivalent to anything from 28 to 31 days, and 1 year can be 365 or 366
|
||
|
|
days, depending on the starting date.
|
||
|
|
|
||
|
|
The inconsistency is handled by shifting the first tag found with the actual
|
||
|
|
specified shift, then calculating the equivalent time difference in seconds
|
||
|
|
for this shift and applying this difference to subsequent tags in a batch
|
||
|
|
conversion. So if it works as designed, the behaviour should be both
|
||
|
|
intuitive and mathematically correct, and the user shouldn't have to worry
|
||
|
|
about details such as this (in keeping with Perl's "do the right thing"
|
||
|
|
philosophy).
|
||
|
|
|
||
|
|
=head1 BUGS
|
||
|
|
|
||
|
|
Due to the use of the standard time library functions, dates are typically
|
||
|
|
limited to the range 1970 to 2038 on 32-bit systems.
|
||
|
|
|
||
|
|
=head1 AUTHOR
|
||
|
|
|
||
|
|
Copyright 2003-2018, Phil Harvey (phil at owl.phy.queensu.ca)
|
||
|
|
|
||
|
|
This library is free software; you can redistribute it and/or modify it
|
||
|
|
under the same terms as Perl itself.
|
||
|
|
|
||
|
|
=head1 SEE ALSO
|
||
|
|
|
||
|
|
L<Image::ExifTool(3pm)|Image::ExifTool>
|
||
|
|
|
||
|
|
=cut
|