tcl/bitsbytes.tcl

   1 # SPDX-License-Identifier: GPL-2.0-or-later
   2
   3 #----------------------------------------
   4 # Purpose - Create some $BIT variables
   5 #           Create $K and $M variables
   6 #          and some bit field extraction variables.
   7 # Create helper variables ...
   8 #    BIT0.. BIT31
   9
  10 for { set x 0  } { $x < 32 } { set x [expr {$x + 1}]} {
  11     set vn [format "BIT%d" $x]
  12     global $vn
  13     set $vn   [expr {1 << $x}]
  14 }
  15
  16 # Create K bytes values
  17 #    __1K ... to __2048K
  18 for { set x 1  } { $x < 2048 } { set x [expr {$x * 2}]} {
  19     set vn [format "__%dK" $x]
  20     global $vn
  21     set $vn   [expr {1024 * $x}]
  22 }
  23
  24 # Create M bytes values
  25 #    __1M ... to __2048K
  26 for { set x 1  } { $x < 2048 } { set x [expr {$x * 2}]} {
  27     set vn [format "__%dM" $x]
  28     global $vn
  29     set $vn [expr {1024 * 1024 * $x}]
  30 }
  31
  32 proc create_mask { MSB LSB } {
  33     return [expr {((1 << ($MSB - $LSB + 1))-1) << $LSB}]
  34 }
  35
  36 # Cut Bits $MSB to $LSB out of this value.
  37 # Example: % format "0x%08x" [extract_bitfield 0x12345678 27 16]
  38 # Result:  0x02340000
  39
  40 proc extract_bitfield { VALUE MSB LSB } {
  41     return [expr {[create_mask $MSB $LSB] & $VALUE}]
  42 }
  43
  44
  45 # Cut bits $MSB to $LSB out of this value
  46 # and shift (normalize) them down to bit 0.
  47 #
  48 # Example: % format "0x%08x" [normalize_bitfield 0x12345678 27 16]
  49 # Result:  0x00000234
  50 #
  51 proc normalize_bitfield { VALUE MSB LSB } {
  52     return [expr {[extract_bitfield $VALUE $MSB $LSB ] >> $LSB}]
  53 }
  54
  55 proc show_normalize_bitfield { VALUE MSB LSB } {
  56     set m [create_mask $MSB $LSB]
  57     set mr [expr {$VALUE & $m}]
  58     set sr [expr {$mr >> $LSB}]
  59     echo [format "((0x%08x & 0x%08x) -> 0x%08x) >> %2d => (0x%x) %5d " $VALUE $m $mr $LSB $sr $sr]
  60    return $sr
  61 }