New semantics for the integer 'for' loop

The numerical 'for' loop over integers now uses a precomputed counter
to control its number of iteractions. This change eliminates several
weird cases caused by overflows (wrap-around) in the control variable.
(It also ensures that every integer loop halts.)

Also, the special opcodes for the usual case of step==1 were removed.
(The new code is already somewhat complex for the usual case,
but efficient.)

testes/nextvar.lua

@@ -76,7 +76,7 @@ while a < lim do
   a = math.ceil(a*1.3)
 end
 
- 
+
 local function check (t, na, nh)
   local a, h = T.querytab(t)
   if a ~= na or h ~= nh then
@@ -100,7 +100,7 @@ local s = 'return {'
 for i=1,lim do
   s = s..i..','
   local s = s
-  for k=0,lim do 
+  for k=0,lim do
     local t = load(s..'}', '')()
     assert(#t == i)
     check(t, fb(i), mp2(k))
@@ -279,7 +279,7 @@ do   -- clear global table
 end
 
 
--- 
+--
 
 local function checknext (a)
   local b = {}
@@ -500,7 +500,7 @@ else --[
   mt.__newindex = nil
   mt.__len = nil
   local tab2 = {}
-  local u2 = T.newuserdata(0) 
+  local u2 = T.newuserdata(0)
   debug.setmetatable(u2, {__newindex = function (_, k, v) tab2[k] = v end})
   table.move(u, 1, 4, 1, u2)
   assert(#tab2 == 4 and tab2[1] == tab[1] and tab2[4] == tab[4])
@@ -601,6 +601,69 @@ do  -- checking types
 
 end
 
+
+do   -- testing other strange cases for numeric 'for'
+
+  local function checkfor (from, to, step, t)
+    local c = 0
+    for i = from, to, step do
+      c = c + 1
+      assert(i == t[c])
+    end
+    assert(c == #t)
+  end
+
+  local maxi = math.maxinteger
+  local mini = math.mininteger
+
+  checkfor(mini, maxi, maxi, {mini, -1, maxi - 1})
+
+  checkfor(mini, math.huge, maxi, {mini, -1, maxi - 1})
+
+  checkfor(maxi, mini, mini, {maxi, -1})
+
+  checkfor(maxi, mini, -maxi, {maxi, 0, -maxi})
+
+  checkfor(maxi, -math.huge, mini, {maxi, -1})
+
+  checkfor(maxi, mini, 1, {})
+  checkfor(mini, maxi, -1, {})
+
+  checkfor(maxi - 6, maxi, 3, {maxi - 6, maxi - 3, maxi})
+  checkfor(mini + 4, mini, -2, {mini + 4, mini + 2, mini})
+
+  local step = maxi // 10
+  local c = mini
+  for i = mini, maxi, step do
+    assert(i == c)
+    c = c + step
+  end
+
+  c = maxi
+  for i = maxi, mini, -step do
+    assert(i == c)
+    c = c - step
+  end
+
+  checkfor(maxi, maxi, maxi, {maxi})
+  checkfor(maxi, maxi, mini, {maxi})
+  checkfor(mini, mini, maxi, {mini})
+  checkfor(mini, mini, mini, {mini})
+end
+
+
+checkerror("'for' step is zero", function ()
+  for i = 1, 10, 0 do end
+end)
+
+checkerror("'for' step is zero", function ()
+  for i = 1, -10, 0 do end
+end)
+
+checkerror("'for' step is zero", function ()
+  for i = 1.0, -10, 0.0 do end
+end)
+
 collectgarbage()
 
 
@@ -657,7 +720,7 @@ a[3] = 30
 -- testing ipairs with metamethods
 a = {n=10}
 setmetatable(a, { __index = function (t,k)
-                     if k <= t.n then return k * 10 end 
+                     if k <= t.n then return k * 10 end
                   end})
 i = 0
 for k,v in ipairs(a) do