=item vec EXPR,OFFSET,BITS
-Treats the string in EXPR as a vector of unsigned integers, and
-returns the value of the bit field specified by OFFSET. BITS
-specifies the number of bits that are reserved for each entry in the
-bit vector. This must be a power of two from 1 to 32 (or 64, if your
-platform supports that).
+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).
C<vec> may also be assigned to, in which case parentheses are needed
to give the expression the correct precedence as in
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($foo, 8, 8) = 0x50; # 'PerlPerlP'
If you know the exact length in bits, it can be used in place of the C<*>.
+Here is an example to illustrate how the bits actually fall in place:
+
+ #!/usr/bin/perl -wl
+
+ print <<'EOT';
+ 0 1 2 3
+ unpack("V",$_) 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, $res
+ .
+ __END__
+
+Regardless of the machine architecture on which it is run, the above
+example should print the following table:
+
+ 0 1 2 3
+ unpack("V",$_) 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
+
=item wait
Behaves like the wait(2) system call on your system: it waits for a child
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