general: Avoid shift undefined behavior

Shifts by 64 are not allowed, so add a conditional guard. Likewise,
left-shifting negative numbers is not allowed in C (unlike C++20, where
it is defined), so avoid such cases.

decode.c

@@ -24,7 +24,8 @@ static uint64_t immlogical(unsigned sf, unsigned N, unsigned immr,
  unsigned esize = 1 << len;
  uint64_t welem = ((uint64_t)1 << (s + 1)) - 1;
  // ROR(welem, r) as bits(esize)
- welem = (welem >> r) | (welem << (esize - r));
+ if (r)
+ welem = (welem >> r) | (welem << (esize - r));
  if (esize < 64)
  welem &= ((uint64_t)1 << esize) - 1;
  // Replicate(ROR(welem, r))

parse.py

@@ -548,10 +548,10 @@ def add_mnem(self, grp: str, name: str, grpdesc: Desc, descmask: MaskedVal, ops:
  # use XOR s.t. immadd can toggle between add and sub.
  buildexprs = ["(" + "^".join([f"{descmask.val:#x}"] + grandExpansions) + ")"]
  for de in grpdesc:
- bitmask = ((1 << de.size) - 1) << de.idx
+ bitmask = (1 << de.size) - 1
  if de.name in assignments:
- buildexprs.append(f"(({assignments[de.name]})<<{de.idx}&{bitmask:#x})")
- elif descmask.mask & bitmask != bitmask:
+ buildexprs.append(f"((({assignments[de.name]})&{bitmask:#x})<<{de.idx})")
+ elif descmask.mask & (bitmask << de.idx) != (bitmask << de.idx):
  print("Encode desc missing for", grp, name, de.name, assignments)
  return
  expr = "|".join(buildexprs)