Introduce vshift()

[perl/modules/Scalar-Vec-Util.git] / lib / Scalar / Vec / Util.pm

diff --git a/lib/Scalar/Vec/Util.pm b/lib/Scalar/Vec/Util.pm
index db6adba1de6489b764f298bc60f314ce393935a5..c80d6424c1c4dc920c4b9729053a7fd271b00a81 100644 (file)
--- a/lib/Scalar/Vec/Util.pm
+++ b/lib/Scalar/Vec/Util.pm
@@ -106,6 +106,34 @@ sub vcopy_pp {
  }
 }
 
+=head2 C<< vshift $v, $start, $length => $bits [, $insert ] >>
+
+In the area starting at C<$start> and of length C<$length> in C<$v>, shift bits C<abs $bits> positions left if C<< $bits > 0 >> and right otherwise.
+If C<$insert> is defined, also fills the resulting gap with ones if C<$insert> is true and zeros if it's false.
+Bits outside of the specified area are left untouched.
+Doesn't need to allocate any extra memory.
+
+=cut
+
+sub vshift {
+ my ($start, $length, $bits, $insert) = @_[1 .. 4];
+ return unless $bits;
+ my $left = 1;
+ if ($bits < 0) {
+  $left = 0;
+  $bits = -$bits;
+ }
+ $bits    = $length if $bits > $length;
+ $length -= $bits;
+ if ($left) {
+  vcopy($_[0], $start, $_[0], $start + $bits, $length);
+  vfill($_[0], $start, $bits, $insert) if defined $insert;
+ } else {
+  vcopy($_[0], $start + $bits, $_[0], $start, $length);
+  vfill($_[0], $start + $length, $bits, $insert) if defined $insert;
+ }
+}
+
 =head2 C<< veq $v1 => $v1_start, $v2 => $v2_start, $length >>
 
 Returns true if the C<$length> bits starting at C<$v1_start> in C<$v1> and C<$v2_start> in C<$v2> are equal, and false otherwise.
@@ -126,7 +154,7 @@ sub veq_pp {
 
 =head1 EXPORT
 
-The functions L</vfill>, L</vcopy> and L</veq> are only exported on request.
+The functions L</vfill>, L</vcopy>, L</vshift> and L</veq> are only exported on request.
 All of them are exported by the tags C<':funcs'> and C<':all'>.
 
 The constants L</SVU_PP> and L</SVU_SIZE> are also only exported on request.
@@ -138,7 +166,7 @@ use base qw/Exporter/;
 
 our @EXPORT         = ();
 our %EXPORT_TAGS    = (
- 'funcs'  => [ qw/vfill vcopy veq/ ],
+ 'funcs'  => [ qw/vfill vcopy vshift veq/ ],
  'consts' => [ qw/SVU_PP SVU_SIZE/ ]
 );
 our @EXPORT_OK      = map { @$_ } values %EXPORT_TAGS;