This procedure is defined in the server but not documented via ad_proc or proc_doc and may be intended as a private interface.
The procedure is defined as:
proc md5::bytes {v} {
#format %c%c%c%c [byte 0 $v] [byte 1 $v] [byte 2 $v] [byte 3 $v]
format %c%c%c%c [expr {0xFF & $v}] [expr {(0xFF00 & $v) >> 8}] [expr {(0xFF0000 & $v) >> 16}] [expr {((0xFF000000 & $v) >> 24) & 0xFF}]
}