fix boolean expression optimization bug

codeGenCpu6502/src/prog8/codegen/cpu6502/assignment/AssignmentAsmGen.kt

@@ -738,7 +738,6 @@ internal class AssignmentAsmGen(private val program: PtProgram,
             assignTrue.add(target)
             assignTrue.add(PtNumber.fromBoolean(true, assign.position))
         } else {
-            require(assign.target.datatype in ByteDatatypes)
             when(assign.target.kind) {
                 TargetStorageKind.VARIABLE -> {
                     if(assign.target.datatype in WordDatatypes) {

codeOptimizers/src/prog8/optimizer/ExpressionSimplifier.kt

@@ -240,10 +240,13 @@ class ExpressionSimplifier(private val program: Program, private val options: Co
         // optimize boolean constant comparisons
         if(expr.operator=="==") {
             if(rightDt==DataType.BOOL && leftDt==DataType.BOOL) {
-                if(rightVal?.asBooleanValue==true)
-                    return listOf(IAstModification.ReplaceNode(expr, expr.left, parent))
-                else
-                    return listOf(IAstModification.ReplaceNode(expr, PrefixExpression("not", expr.left, expr.position), parent))
+                val rightConstBool = rightVal?.asBooleanValue
+                if(rightConstBool!=null) {
+                    return if(rightConstBool)
+                        listOf(IAstModification.ReplaceNode(expr, expr.left, parent))
+                    else
+                        listOf(IAstModification.ReplaceNode(expr, PrefixExpression("not", expr.left, expr.position), parent))
+                }
             }
             if (rightVal?.number == 1.0) {
                 if (options.strictBool) {

docs/source/libraries.rst

@@ -24,6 +24,10 @@ of these library modules automatically as required.
     The resulting compiled binary program *only works on the target machine it was compiled for*.
     You must recompile the program for every target you want to run it on.
 
+.. note::
+    Several algorithms and math routines in Prog8's assembly library files are adapted from
+    code publicly available on https://www.codebase64.org/
+
 
 Low-fi variable and subroutine definitions in all available library modules
 ---------------------------------------------------------------------------

examples/test.p8

@@ -1,20 +1,17 @@
-%zeropage basicsafe
 %import textio
+%zeropage basicsafe
 
 main {
-    sub start() {
-        uword @shared a,b
-        b = a                   ; works
-        cx16.r1L = lsb(a)       ; works
-        funcw(a)                ; works
-        funcb(lsb(a))           ; fails :-(
-    }
+  sub show_bug(byte a, byte b) {
+      if (a >= 0) == (b > 0) {
+          txt.print("bug!")
+      } else {
+          txt.print("no bug.")
+      }
+      txt.nl()
+  }
 
-    sub funcw(uword arg) {
-        arg++
-    }
-
-    sub funcb(ubyte arg) {
-        arg++
-    }
+  sub start() {
+      show_bug(-1, 4)
+  }
 }