tcl/bitsbytes.tcl

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