src/nmutil/extend.py

   1 # SPDX-License-Identifier: LGPL-2-or-later
   2 # Copyright (C) Luke Kenneth Casson Leighton 2020,2021 <lkcl@lkcl.net>
   3 """
   4 Provides sign/unsigned extension/truncation utility functions.
   5
   6 This work is funded through NLnet under Grant 2019-02-012
   7 """
   8 from nmigen import Repl, Cat, Const
   9
  10
  11 def exts(exts_data, width, fullwidth):
  12     diff = fullwidth-width
  13     if diff == 0:
  14         return exts_data
  15     exts_data = exts_data[0:width]
  16     if diff <= 0:
  17         return exts_data[:fullwidth]
  18     topbit = exts_data[-1]
  19     signbits = Repl(topbit, diff)
  20     return Cat(exts_data, signbits)
  21
  22
  23 def extz(extz_data, width, fullwidth):
  24     diff = fullwidth-width
  25     if diff == 0:
  26         return extz_data
  27     extz_data = extz_data[0:width]
  28     if diff <= 0:
  29         return extz_data[:fullwidth]
  30     topbit = Const(0)
  31     signbits = Repl(topbit, diff)
  32     return Cat(extz_data, signbits)
  33
  34
  35 def ext(data, shape, newwidth):
  36     """extend/truncate data to new width, preserving sign
  37     """
  38     width, signed = shape
  39     if signed:
  40         return exts(data, width, newwidth)
  41     return extz(data, width, newwidth)