added offsetof() to get the byte offset of struct members.

compiler/src/prog8/functions/BuiltinFunctions.kt

@@ -102,6 +102,7 @@ private val functionSignatures: List<FSignature> = listOf(
     FSignature("abs"         , true, listOf(FParam("value", NumericDatatypes)), null, ::builtinAbs),      // type depends on argument
     FSignature("len"         , true, listOf(FParam("values", IterableDatatypes)), null, ::builtinLen),    // type is UBYTE or UWORD depending on actual length
     FSignature("sizeof"      , true, listOf(FParam("object", DataType.values().toSet())), DataType.UBYTE, ::builtinSizeof),
+    FSignature("offsetof"    , true, listOf(FParam("object", DataType.values().toSet())), DataType.UBYTE, ::builtinOffsetof),
         // normal functions follow:
     FSignature("sgn"         , true, listOf(FParam("value", NumericDatatypes)), DataType.BYTE, ::builtinSgn ),
     FSignature("sin"         , true, listOf(FParam("rads", setOf(DataType.FLOAT))), DataType.FLOAT) { a, p, prg -> oneDoubleArg(a, p, prg, Math::sin) },
@@ -278,6 +279,28 @@ private fun builtinAbs(args: List<Expression>, position: Position, program: Prog
     }
 }
 
+private fun builtinOffsetof(args: List<Expression>, position: Position, program: Program): NumericLiteralValue {
+    // 1 arg, type = anything, result type = ubyte
+    if(args.size!=1)
+        throw SyntaxError("offsetof requires one argument", position)
+    val idref = args[0] as? IdentifierReference
+        ?: throw SyntaxError("offsetof argument should be an identifier", position)
+
+    val vardecl = idref.targetVarDecl(program.namespace)!!
+    val struct = vardecl.struct
+    if (struct == null || vardecl.datatype == DataType.STRUCT)
+        throw SyntaxError("offsetof can only be used on struct members", position)
+
+    val membername = idref.nameInSource.last()
+    var offset = 0
+    for(member in struct.statements) {
+        if((member as VarDecl).name == membername)
+            return NumericLiteralValue(DataType.UBYTE, offset, position)
+        offset += member.datatype.memorySize()
+    }
+    throw SyntaxError("undefined struct member", position)
+}
+
 private fun builtinSizeof(args: List<Expression>, position: Position, program: Program): NumericLiteralValue {
     // 1 arg, type = anything, result type = ubyte
     if(args.size!=1)

docs/source/programming.rst

@@ -843,6 +843,11 @@ sizeof(name)
     For an 10 element array of floats, it is 50 (on the C-64, where a float is 5 bytes).
     Note: usually you will be interested in the number of elements in an array, use len() for that.
 
+offsetof(membername)
+    Number of bytes from the start of a struct variable that this member variable is located.
+    For now, this only works on members of a declared struct variable and not yet on members
+    referenced from the struct type itself.  This might be improved in a future version of the language.
+
 swap(x, y)
     Swap the values of numerical variables (or memory locations) x and y in a fast way.
 

docs/source/todo.rst

@@ -2,7 +2,6 @@
 TODO
 ====
 
-- add offsetof() to get the byte offset of struct members.
 - add any2(), all2(), max2(), min2(), reverse2(), sum2(), sort2() that take (array, startindex, length) arguments
 - optimize for loop iterations better to allow proper inx, cpx #value, bne loop  instructions  (like repeat loop)
 - why is there a beq  _prog8_label_2_repeatend  at the end of repeat loops? seems unused

examples/test.p8

@@ -1,6 +1,7 @@
 %import textio
 %import diskio
 %import string
+%import floats
 %zeropage basicsafe
 %option no_sysinit
 
@@ -9,14 +10,41 @@ main {
 
     sub start() {
 
-        diskio.directory(8)
-        diskio.save(8, "blabla", $2000, 1024)
-        diskio.directory(8)
-        diskio.rename(8, "blabla", "newname")
-        diskio.directory(8)
-        diskio.delete(8, "newname")
-        diskio.directory(8)
+        struct SaveData {
+            ubyte galaxy
+            ubyte planet
+            uword cash
+            float flt
+            ubyte fuel
+        }
+
+        SaveData data
+
+        txt.print("size of struct: ")
+        txt.print_ub(sizeof(SaveData))
+        txt.chrout(';')
+        txt.print_ub(sizeof(data))
+        txt.chrout('\n')
+
+        txt.print("offset of galaxy: ")
+        txt.print_ub(offsetof(data.galaxy))
+        txt.chrout('\n')
+
+        txt.print("offset of planet: ")
+        txt.print_ub(offsetof(data.planet))
+        txt.chrout('\n')
+
+        txt.print("offset of cash: ")
+        txt.print_ub(offsetof(data.cash))
+        txt.chrout('\n')
+
+        txt.print("offset of flt: ")
+        txt.print_ub(offsetof(data.flt))
+        txt.chrout('\n')
+
+        txt.print("offset of fuel: ")
+        txt.print_ub(offsetof(data.fuel))
+        txt.chrout('\n')
 
-        txt.print("---------------------------------\n")
     }
 }