During debugging, encountered a grievous documentation error:
Code:
function TChepersyMemoryManagerChunk.Alloc: pointer;
var 
  i, k: integer;
  j: cardinal;
  m: ptruint;
begin
  i:= 0;
  // the mask bits of non-valid indexes are pre-set to 1, see the constructor
  for i:= 0 to High(f_AllocMask) do begin
    m:= not f_AllocMask[i];

    if m = 0 then continue; 
    // https://www.freepascal.org/docs-html/current/rtl/system/bsfdword.html
    // incorrectly states that BsfDWord returns 255 if no bits are set
    // while in fact it returns 0! (at least in fp 2.6.4 it does)
        j:= {$ifdef cpu64}BsfQWord( {$else}BsfDWord( {$endif} m );
addlog(' i=%0, j=%1, k=%2, mask=%3',[i,j,k,pointer(f_AllocMask[i])])    ;
//    if j < 255 then begin
      k:= (i * 8 * sizeof(pointer)) + j;
      Assert((k >= f_IdxLow) and (k <= f_IdxHigh)
            , 'TChepersyMemoryManagerChunk.Alloc: index ' + IntToStr(k) 
            + ' is out of bounds (' + IntToStr(f_IdxLow) + ',' 
            + IntToStr(f_IdxHigh) + ')');
      Inc(f_AllocCount);
      Dec(f_FreeCount);
      if f_FreeCount = 0 then CpsMemoryManager.OnChunkBecomingFull(Self);
      f_AllocMask[i]:= f_AllocMask[i] or (ptruint(1) shl j); 
      Exit(pointer(ptruint(Self) + ptruint(k) * f_Size));
//    end;
  end;
  Die(MI_ERROR_PROGRAMMER_NO_BAKA, [
                           'TChepersyMemoryManagerChunk.Alloc algorithm fail']);
end;
..aaand I'd say this is more than just twitching:

YEEEE-HAW!