## Version 22 of Playing with bits

Updated 2008-10-06 08:52:01 by mistachkin

if 0 { Richard Suchenwirth 2002-12-07 - Here is another educational Tcltoy: a set of 8 checkboxes that represent the bits of a byte. Each is labeled with its positional value below. The button at bottom displays the current value of the byte in hexadecimal, octal and decimal. Clicking on it resets all bits to 0, or, if they already are, to 1.

The simple code below contains some tricks that are unique to Tcl. The positional values of the 8 bits serve as variable names as well, and with prefixed "." as widget names of the checkboxes. The two procedures first import the global list of positional values, then via eval global each of them separately. As name and onvalue of a "bit" are the same, the otherwise puzzling command

` set \$i \$i`

makes perfect sense - if i is 16, it assigns the value 16 to the variable 16... }

``` set positionalValues {128 64 32 16 8 4 2 1}
foreach i \$positionalValues {
checkbutton .\$i -variable \$i -onvalue \$i -command compute
lappend buttons .\$i
lappend labels [label .l\$i -text \$i]
}
eval grid \$buttons
eval grid \$labels
button .result -textvar result -command reset -borderwidth 1
grid .result -columnspan 8 -sticky ew

proc reset {} {
global positionalValues result
eval global \$positionalValues
foreach i \$positionalValues {
if {[lindex \$result end] == 0} {
set \$i \$i
} else {set \$i 0}
}
compute
}
proc compute {} {
global positionalValues result
eval global \$positionalValues
set res 0
foreach i \$positionalValues {
incr res [set \$i]
}
set result [format "Hex: 0x%02X, Octal: 0o%02o, Decimal: %d (%c)" \$res \$res \$res \$res]
}
compute ;# show the initial state (should be 0)
bind . <Escape> {exec wish \$argv0 &; exit}```

2002-12-09 JJM, Fixed typo in the hex and octal format strings. - RS: Thanks! I originally started this at home in all leisure, but when at work I hurriedly try to insert fixes (and don't test well - the screenshot above still shows the octal bug!), such things happen... Thanks again for attention, and new ideas!

2002-12-09 JJM, By changing these lines:

``` grid .result -columnspan 8 -sticky ew
set result [format "Hex: 0x%2X, Octal: 0o%02o, Decimal: %d (%c)" \$res \$res \$res \$res]```

to these:

``` grid .result -columnspan [llength \$positionalValues] -sticky ew
set result [format "Hex: 0x%02X, Octal: 0o%02o, Decimal: %d" \$res \$res \$res]```

You can add an arbitrary number of values to the positionalValues list and the code will still work properly.

It looks like this:

2007-01-08 JDR - Give this a try.

Replace this line

set positionalValues {128 64 32 16 8 4 2 1}

With this for loop, set i to whatever number you want to a maximum value of 31.

for {set i 31} {\$i > 0} {incr i -1} {

`   lappend positionalValues \$i`

}

Replace this line

`   checkbutton .\$i -variable \$i -onvalue \$i -command compute`

With this

`   checkbutton .\$i -variable \$i -onvalue [expr {int(pow(2,(\$i - 1)))}] -command compute`

Replace this line

`           set \$i \$i`

With this

`           set \$i [expr {int(pow(2,(\$i - 1)))}]`

One final note, you might want to change the positionalValues name to positionalLabels

2002-12-09 JJM, Far more radical modifications:

``` set positionalValues(1) {0x00000008 0x00000004 0x00000002 0x00000001}
set positionalValues(2) {0x00000080 0x00000040 0x00000020 0x00000010}
set positionalValues(3) {0x00000800 0x00000400 0x00000200 0x00000100}
set positionalValues(4) {0x00008000 0x00004000 0x00002000 0x00001000}
set positionalValues(5) {0x00080000 0x00040000 0x00020000 0x00010000}
set positionalValues(6) {0x00800000 0x00400000 0x00200000 0x00100000}
set positionalValues(7) {0x08000000 0x04000000 0x02000000 0x01000000}
set positionalValues(8) {0x80000000 0x40000000 0x20000000 0x10000000}

set row 0

foreach j [lsort -integer [array names positionalValues]] {
set buttons {}
set labels {}

foreach i \$positionalValues(\$j) {
checkbutton .\$i -variable \$i -onvalue \$i -command compute -borderwidth 2
lappend buttons .\$i
lappend labels [label .l\$i -text \$i]
}

eval grid \$buttons -row \$row -columnspan [llength \$positionalValues(1)]
eval grid \$labels -row [expr {\$row + 1}] -columnspan [llength \$positionalValues(1)]

set row [expr {\$row + 2}]
}

button .result -textvar result -command reset -borderwidth 1
grid .result -row [expr {\$row + 2}] -columnspan [expr {[llength \$positionalValues(1)] * 4}] -sticky ew

proc reset {} {
global positionalValues result

foreach j [lsort -integer [array names positionalValues]] {
eval global \$positionalValues(\$j)

foreach i \$positionalValues(\$j) {
if {[lindex \$result end] == 0} {
set \$i \$i
} else {
set \$i 0
}
}
}

compute
}

proc compute {} {
global positionalValues result

set res 0
foreach j [lsort -integer [array names positionalValues]] {
eval global \$positionalValues(\$j)

foreach i \$positionalValues(\$j) {
set res [expr {wide(\$res) + wide([set \$i])}]
}
}

set result [format "Hex: 0x%1\$02X, Octal: 0o%1\$02o, Decimal: %1\$ld" \$res]
}

compute ;# show the initial state (should be 0)
bind . <Escape> {exec wish \$argv0 &; exit}```

escargo 16 Aug 2005 - Changed the last format statement to use positional specifiers instead of sequential ones.

AMG: Relax with bits!