src/nmutil/divmod.py

   1 # SPDX-License-Identifier: LGPL-3-or-later
   2 """
   3     This work is funded through NLnet under Grant 2019-02-012
   4
   5     License: LGPLv3+
   6
   7
   8 """
   9
  10 from copy import copy
  11 # this is a POWER ISA 3.0B compatible *signed* div function
  12 # however it is also the c, c++, rust, java *and* x86 way of doing things
  13
  14
  15 def trunc_divs(n, d):
  16     abs_n = abs(n.to_signed_int())
  17     abs_d = abs(d.to_signed_int())
  18     print("trunc_div n", abs_n, n.to_signed_int())
  19     print("trunc_div d", abs_d, d.to_signed_int())
  20     abs_q = abs_n // abs_d
  21     sign_n = n.value & (1 << (n.bits - 1)) != 0
  22     sign_d = d.value & (1 << (d.bits - 1)) != 0
  23     print("trunc_div", hex(n.value), hex(d.value),
  24           hex(abs_n), hex(abs_d), hex(abs_q),
  25           sign_n, sign_d)
  26     res = copy(n)
  27     if (sign_n == sign_d):
  28         res.value = abs_q
  29         if res.value & (1 << (res.bits - 1)) != 0:
  30             # result should be positive but is negative
  31             raise OverflowError()
  32         return res
  33     mask = (1 << res.bits) - 1
  34     res.value = (-abs_q) & mask
  35
  36     return res
  37
  38
  39 # this is a POWER ISA 3.0B compatible *signed* mod / remainder function
  40 # however it is also the c, c++, rust, java *and* x86 way of doing things
  41 def trunc_rems(n, d):
  42     m = d * trunc_divs(n, d)
  43
  44     # cheat - really shouldn't do this. mul returns full length
  45     m.bits = n.bits
  46     return n - m