Fix lua modulo

Author: Unrud

_glua-tests/issues.lua

@@ -387,3 +387,20 @@ function test()
     assert(a == 1 and b == nil and c == nil)
 end
 test()
+
+-- issue #412
+-- issue #418
+-- Conversion from symmetric modulo is incorrect.
+function test()
+    assert(-2 % -2 == 0)
+    assert(-1 % -2 == -1)
+    assert(0 % -2 == 0)
+    assert(1 % -2 == -1)
+    assert(2 % -2 == 0)
+    assert(-2 % 2 == 0)
+    assert(-1 % 2 == 1)
+    assert(0 % 2 == 0)
+    assert(1 % 2 == 1)
+    assert(2 % 2 == 0)
+end
+test()

_vm.go

@@ -840,7 +840,7 @@ func luaModulo(lhs, rhs LNumber) LNumber {
 	flhs := float64(lhs)
 	frhs := float64(rhs)
 	v := math.Mod(flhs, frhs)
-	if flhs < 0 || frhs < 0 && !(flhs < 0 && frhs < 0) {
+	if frhs > 0 && v < 0 || frhs < 0 && v > 0 {
 		v += frhs
 	}
 	return LNumber(v)

vm.go

@@ -1533,7 +1533,7 @@ func luaModulo(lhs, rhs LNumber) LNumber {
 	flhs := float64(lhs)
 	frhs := float64(rhs)
 	v := math.Mod(flhs, frhs)
-	if flhs < 0 || frhs < 0 && !(flhs < 0 && frhs < 0) {
+	if frhs > 0 && v < 0 || frhs < 0 && v > 0 {
 		v += frhs
 	}
 	return LNumber(v)