- vec EXPR,OFFSET,BITS
-
Treats the string in EXPR as a bit vector made up of elements of width BITS and returns the value of the element specified by OFFSET as an unsigned integer. BITS therefore specifies the number of bits that are reserved for each element in the bit vector. This must be a power of two from 1 to 32 (or 64, if your platform supports that).
文字列 EXPR を BITS 幅の要素からなるビットベクターとして扱い、 OFFSET で指定された要素を符号なし整数として返します。 従って、 BITS はビットベクターの中の各要素について予約されるビット数です。 BIT は、1 から 32 まで(プラットホームが 対応していれば 64 まで) の 2 のべき乗でなければなりません。
If BITS is 8, "elements" coincide with bytes of the input string.
BITS が 8 の場合、「要素」は入力文字列の各バイトと一致します。
If BITS is 16 or more, bytes of the input string are grouped into chunks of size BITS/8, and each group is converted to a number as with pack/unpack with big-endian formats
n/N(and analogously for BITS==64). See pack for details.BITS が 16 以上の場合、入力のバイト列は BITS/8 のサイズの固まりに グループ化され、各グループは pack/ unpack のビッグエンディアン フォーマット
n/Nを用いて(BITS==64 の類似として)数値に変換されます。 詳細は pack を参照してください。If bits is 4 or less, the string is broken into bytes, then the bits of each byte are broken into 8/BITS groups. Bits of a byte are numbered in a little-endian-ish way, as in
0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80. For example, breaking the single input bytechr(0x36)into two groups gives a list(0x6, 0x3); breaking it into 4 groups gives(0x2, 0x1, 0x3, 0x0).BITS が 4 以下の場合、文字列はバイトに分解され、バイトの各ビットは 8/BITS 個のグループに分割されます。 ビットはリトルエンディアン風に、
0x01,0x02,0x04,0x08,0x10,0x20,0x40,0x80の順になります。 例えば、入力バイトchr(0x36)を二つのグループに分割すると、(0x6, 0x3)になります; 4 つに分割すると(0x2, 0x1, 0x3, 0x0)に なります。vec may also be assigned to, in which case parentheses are needed to give the expression the correct precedence as in
vec は左辺値として、代入の 対象にすることもできます; この場合、式を正しく 先行させるために以下のように括弧が必要です:
vec($image, $max_x * $x + $y, 8) = 3;If the selected element is outside the string, the value 0 is returned. If an element off the end of the string is written to, Perl will first extend the string with sufficiently many zero bytes. It is an error to try to write off the beginning of the string (i.e., negative OFFSET).
選択された要素が文字列の外側だった場合、値 0 が返されます。 文字列の最後よりも後ろの要素に書き込もうとした場合、 Perl はまず文字列を必要な分だけ 0 のバイトで拡張します。 文字列の先頭より前に書き込もうとした(つまり OFFSET が負の数だった) 場合はエラーとなります。
If the string happens to be encoded as UTF-8 internally (and thus has the UTF8 flag set), vec tries to convert it to use a one-byte-per-character internal representation. However, if the string contains characters with values of 256 or higher, a fatal error will occur.
文字列がたまたま内部で UTF-8 でエンコードされている場合(したがって UTF8 フラグがセットされている場合)、 vec はこれを単一バイト文字内部表現に 変換しようとします。 しかし、この文字列に値が 256 以上の文字が含まれている場合、 致命的エラーが発生します。
Strings created with vec can also be manipulated with the logical operators
|,&,^, and~. These operators will assume a bit vector operation is desired when both operands are strings. See "Bitwise String Operators" in perlop.vec で作られた文字列は、論理演算子
|、&、^,~で扱うこともできます。 これらの演算子は、両方の被演算子に文字列を使うと、 ビットベクター演算を行ないます。 "Bitwise String Operators" in perlop を参照してください。The following code will build up an ASCII string saying
'PerlPerlPerl'. The comments show the string after each step. Note that this code works in the same way on big-endian or little-endian machines.次のコードは
'PerlPerlPerl'という ASCII 文字列を作成します。 コメントは各行の実行後の文字列を示します。 このコードはビッグエンディアンでもリトルエンディアンでも同じように 動作することに注意してください。my $foo = ''; vec($foo, 0, 32) = 0x5065726C; # 'Perl' # $foo eq "Perl" eq "\x50\x65\x72\x6C", 32 bits print vec($foo, 0, 8); # prints 80 == 0x50 == ord('P') vec($foo, 2, 16) = 0x5065; # 'PerlPe' vec($foo, 3, 16) = 0x726C; # 'PerlPerl' vec($foo, 8, 8) = 0x50; # 'PerlPerlP' vec($foo, 9, 8) = 0x65; # 'PerlPerlPe' vec($foo, 20, 4) = 2; # 'PerlPerlPe' . "\x02" vec($foo, 21, 4) = 7; # 'PerlPerlPer' # 'r' is "\x72" vec($foo, 45, 2) = 3; # 'PerlPerlPer' . "\x0c" vec($foo, 93, 1) = 1; # 'PerlPerlPer' . "\x2c" vec($foo, 94, 1) = 1; # 'PerlPerlPerl' # 'l' is "\x6c"To transform a bit vector into a string or list of 0's and 1's, use these:
ビットベクターを、0 と 1 の文字列や配列に変換するには、 以下のようにします。
my $bits = unpack("b*", $vector); my @bits = split(//, unpack("b*", $vector));If you know the exact length in bits, it can be used in place of the
*.ビット長が分かっていれば、
*の代わりにその長さを使うことができます。Here is an example to illustrate how the bits actually fall in place:
これはビットが実際にどのような位置に入るかを図示する例です。
#!/usr/bin/perl -wl print <<'EOT'; 0 1 2 3 unpack("V",$_) 01234567890123456789012345678901 ------------------------------------------------------------------ EOT for $w (0..3) { $width = 2**$w; for ($shift=0; $shift < $width; ++$shift) { for ($off=0; $off < 32/$width; ++$off) { $str = pack("B*", "0"x32); $bits = (1<<$shift); vec($str, $off, $width) = $bits; $res = unpack("b*",$str); $val = unpack("V", $str); write; } } } format STDOUT = vec($_,@#,@#) = @<< == @######### @>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> $off, $width, $bits, $val, $res . __END__Regardless of the machine architecture on which it runs, the example above should print the following table:
実行するマシンのアーキテクチャに関わらず、 上記の例は以下の表を出力します。
0 1 2 3 unpack("V",$_) 01234567890123456789012345678901 ------------------------------------------------------------------ vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000 vec($_, 1, 1) = 1 == 2 01000000000000000000000000000000 vec($_, 2, 1) = 1 == 4 00100000000000000000000000000000 vec($_, 3, 1) = 1 == 8 00010000000000000000000000000000 vec($_, 4, 1) = 1 == 16 00001000000000000000000000000000 vec($_, 5, 1) = 1 == 32 00000100000000000000000000000000 vec($_, 6, 1) = 1 == 64 00000010000000000000000000000000 vec($_, 7, 1) = 1 == 128 00000001000000000000000000000000 vec($_, 8, 1) = 1 == 256 00000000100000000000000000000000 vec($_, 9, 1) = 1 == 512 00000000010000000000000000000000 vec($_,10, 1) = 1 == 1024 00000000001000000000000000000000 vec($_,11, 1) = 1 == 2048 00000000000100000000000000000000 vec($_,12, 1) = 1 == 4096 00000000000010000000000000000000 vec($_,13, 1) = 1 == 8192 00000000000001000000000000000000 vec($_,14, 1) = 1 == 16384 00000000000000100000000000000000 vec($_,15, 1) = 1 == 32768 00000000000000010000000000000000 vec($_,16, 1) = 1 == 65536 00000000000000001000000000000000 vec($_,17, 1) = 1 == 131072 00000000000000000100000000000000 vec($_,18, 1) = 1 == 262144 00000000000000000010000000000000 vec($_,19, 1) = 1 == 524288 00000000000000000001000000000000 vec($_,20, 1) = 1 == 1048576 00000000000000000000100000000000 vec($_,21, 1) = 1 == 2097152 00000000000000000000010000000000 vec($_,22, 1) = 1 == 4194304 00000000000000000000001000000000 vec($_,23, 1) = 1 == 8388608 00000000000000000000000100000000 vec($_,24, 1) = 1 == 16777216 00000000000000000000000010000000 vec($_,25, 1) = 1 == 33554432 00000000000000000000000001000000 vec($_,26, 1) = 1 == 67108864 00000000000000000000000000100000 vec($_,27, 1) = 1 == 134217728 00000000000000000000000000010000 vec($_,28, 1) = 1 == 268435456 00000000000000000000000000001000 vec($_,29, 1) = 1 == 536870912 00000000000000000000000000000100 vec($_,30, 1) = 1 == 1073741824 00000000000000000000000000000010 vec($_,31, 1) = 1 == 2147483648 00000000000000000000000000000001 vec($_, 0, 2) = 1 == 1 10000000000000000000000000000000 vec($_, 1, 2) = 1 == 4 00100000000000000000000000000000 vec($_, 2, 2) = 1 == 16 00001000000000000000000000000000 vec($_, 3, 2) = 1 == 64 00000010000000000000000000000000 vec($_, 4, 2) = 1 == 256 00000000100000000000000000000000 vec($_, 5, 2) = 1 == 1024 00000000001000000000000000000000 vec($_, 6, 2) = 1 == 4096 00000000000010000000000000000000 vec($_, 7, 2) = 1 == 16384 00000000000000100000000000000000 vec($_, 8, 2) = 1 == 65536 00000000000000001000000000000000 vec($_, 9, 2) = 1 == 262144 00000000000000000010000000000000 vec($_,10, 2) = 1 == 1048576 00000000000000000000100000000000 vec($_,11, 2) = 1 == 4194304 00000000000000000000001000000000 vec($_,12, 2) = 1 == 16777216 00000000000000000000000010000000 vec($_,13, 2) = 1 == 67108864 00000000000000000000000000100000 vec($_,14, 2) = 1 == 268435456 00000000000000000000000000001000 vec($_,15, 2) = 1 == 1073741824 00000000000000000000000000000010 vec($_, 0, 2) = 2 == 2 01000000000000000000000000000000 vec($_, 1, 2) = 2 == 8 00010000000000000000000000000000 vec($_, 2, 2) = 2 == 32 00000100000000000000000000000000 vec($_, 3, 2) = 2 == 128 00000001000000000000000000000000 vec($_, 4, 2) = 2 == 512 00000000010000000000000000000000 vec($_, 5, 2) = 2 == 2048 00000000000100000000000000000000 vec($_, 6, 2) = 2 == 8192 00000000000001000000000000000000 vec($_, 7, 2) = 2 == 32768 00000000000000010000000000000000 vec($_, 8, 2) = 2 == 131072 00000000000000000100000000000000 vec($_, 9, 2) = 2 == 524288 00000000000000000001000000000000 vec($_,10, 2) = 2 == 2097152 00000000000000000000010000000000 vec($_,11, 2) = 2 == 8388608 00000000000000000000000100000000 vec($_,12, 2) = 2 == 33554432 00000000000000000000000001000000 vec($_,13, 2) = 2 == 134217728 00000000000000000000000000010000 vec($_,14, 2) = 2 == 536870912 00000000000000000000000000000100 vec($_,15, 2) = 2 == 2147483648 00000000000000000000000000000001 vec($_, 0, 4) = 1 == 1 10000000000000000000000000000000 vec($_, 1, 4) = 1 == 16 00001000000000000000000000000000 vec($_, 2, 4) = 1 == 256 00000000100000000000000000000000 vec($_, 3, 4) = 1 == 4096 00000000000010000000000000000000 vec($_, 4, 4) = 1 == 65536 00000000000000001000000000000000 vec($_, 5, 4) = 1 == 1048576 00000000000000000000100000000000 vec($_, 6, 4) = 1 == 16777216 00000000000000000000000010000000 vec($_, 7, 4) = 1 == 268435456 00000000000000000000000000001000 vec($_, 0, 4) = 2 == 2 01000000000000000000000000000000 vec($_, 1, 4) = 2 == 32 00000100000000000000000000000000 vec($_, 2, 4) = 2 == 512 00000000010000000000000000000000 vec($_, 3, 4) = 2 == 8192 00000000000001000000000000000000 vec($_, 4, 4) = 2 == 131072 00000000000000000100000000000000 vec($_, 5, 4) = 2 == 2097152 00000000000000000000010000000000 vec($_, 6, 4) = 2 == 33554432 00000000000000000000000001000000 vec($_, 7, 4) = 2 == 536870912 00000000000000000000000000000100 vec($_, 0, 4) = 4 == 4 00100000000000000000000000000000 vec($_, 1, 4) = 4 == 64 00000010000000000000000000000000 vec($_, 2, 4) = 4 == 1024 00000000001000000000000000000000 vec($_, 3, 4) = 4 == 16384 00000000000000100000000000000000 vec($_, 4, 4) = 4 == 262144 00000000000000000010000000000000 vec($_, 5, 4) = 4 == 4194304 00000000000000000000001000000000 vec($_, 6, 4) = 4 == 67108864 00000000000000000000000000100000 vec($_, 7, 4) = 4 == 1073741824 00000000000000000000000000000010 vec($_, 0, 4) = 8 == 8 00010000000000000000000000000000 vec($_, 1, 4) = 8 == 128 00000001000000000000000000000000 vec($_, 2, 4) = 8 == 2048 00000000000100000000000000000000 vec($_, 3, 4) = 8 == 32768 00000000000000010000000000000000 vec($_, 4, 4) = 8 == 524288 00000000000000000001000000000000 vec($_, 5, 4) = 8 == 8388608 00000000000000000000000100000000 vec($_, 6, 4) = 8 == 134217728 00000000000000000000000000010000 vec($_, 7, 4) = 8 == 2147483648 00000000000000000000000000000001 vec($_, 0, 8) = 1 == 1 10000000000000000000000000000000 vec($_, 1, 8) = 1 == 256 00000000100000000000000000000000 vec($_, 2, 8) = 1 == 65536 00000000000000001000000000000000 vec($_, 3, 8) = 1 == 16777216 00000000000000000000000010000000 vec($_, 0, 8) = 2 == 2 01000000000000000000000000000000 vec($_, 1, 8) = 2 == 512 00000000010000000000000000000000 vec($_, 2, 8) = 2 == 131072 00000000000000000100000000000000 vec($_, 3, 8) = 2 == 33554432 00000000000000000000000001000000 vec($_, 0, 8) = 4 == 4 00100000000000000000000000000000 vec($_, 1, 8) = 4 == 1024 00000000001000000000000000000000 vec($_, 2, 8) = 4 == 262144 00000000000000000010000000000000 vec($_, 3, 8) = 4 == 67108864 00000000000000000000000000100000 vec($_, 0, 8) = 8 == 8 00010000000000000000000000000000 vec($_, 1, 8) = 8 == 2048 00000000000100000000000000000000 vec($_, 2, 8) = 8 == 524288 00000000000000000001000000000000 vec($_, 3, 8) = 8 == 134217728 00000000000000000000000000010000 vec($_, 0, 8) = 16 == 16 00001000000000000000000000000000 vec($_, 1, 8) = 16 == 4096 00000000000010000000000000000000 vec($_, 2, 8) = 16 == 1048576 00000000000000000000100000000000 vec($_, 3, 8) = 16 == 268435456 00000000000000000000000000001000 vec($_, 0, 8) = 32 == 32 00000100000000000000000000000000 vec($_, 1, 8) = 32 == 8192 00000000000001000000000000000000 vec($_, 2, 8) = 32 == 2097152 00000000000000000000010000000000 vec($_, 3, 8) = 32 == 536870912 00000000000000000000000000000100 vec($_, 0, 8) = 64 == 64 00000010000000000000000000000000 vec($_, 1, 8) = 64 == 16384 00000000000000100000000000000000 vec($_, 2, 8) = 64 == 4194304 00000000000000000000001000000000 vec($_, 3, 8) = 64 == 1073741824 00000000000000000000000000000010 vec($_, 0, 8) = 128 == 128 00000001000000000000000000000000 vec($_, 1, 8) = 128 == 32768 00000000000000010000000000000000 vec($_, 2, 8) = 128 == 8388608 00000000000000000000000100000000 vec($_, 3, 8) = 128 == 2147483648 00000000000000000000000000000001