allocate even more c64 zeropage locations for floats

compiler/res/prog8lib/c64/graphics.p8

@@ -39,8 +39,8 @@ graphics {
             swap(x1, x2)
             swap(y1, y2)
         }
-        word @zp dx = x2-x1 as word
-        word @zp dy = y2-y1
+        word @zp dx = (x2-x1) as word
+        word @zp dy = (y2-y1) as word
 
         if dx==0 {
             vertical_line(x1, y1, abs(dy)+1 as ubyte)

compiler/src/prog8/compiler/target/c64/C64MachineDefinition.kt

@@ -109,6 +109,7 @@ internal object C64MachineDefinition: IMachineDefinition {
                 if (options.zeropage == ZeropageType.FLOATSAFE) {
                     // remove the zero page locations used for floating point operations from the free list
                     free.removeAll(listOf(
+                            0x22, 0x23, 0x24, 0x25,
                             0x10, 0x11, 0x12, 0x26, 0x27, 0x28, 0x29, 0x2a,
                             0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 0x60,
                             0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68,

examples/test.p8

@@ -1,6 +1,8 @@
-%import graphics
+%target c64
 %import floats
-
+%import graphics
+%import test_stack
+%zeropage floatsafe
 
 main {
     sub start() {
@@ -10,7 +12,9 @@ main {
         uword xx
         ubyte yy
 
-        graphics.line(150,50,150,50)
+        graphics.line(160,100,160,80)
+        graphics.line(160,80,180,81)
+        graphics.line(180,81,177,103)
 
         for yy in 0 to 199-60 step 16 {