implemented MOVFM math routine

STATUS.md

@@ -186,12 +186,12 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B9EA`   | `LOG`        | NOT DONE | XXX - no stub added yet                            |
 | `$BA28`   | `FMUL`       | PARTIAL  | needs `FMULT`                                      |
 | `$BA2B`   | `FMULT`      | NOT DONE | multiplies FAC1 by FAC2                            |
-| `$BA8C`   | `CONUPK`     | PARTIAL  | not tested yet                                     |
+| `$BA8C`   | `CONUPK`     | PARTIAL  | not fully tested yet                               |
 | `$BAE2`   | `MUL10`      | NOT DONE | multiply FAC1 by 10                                |
 | `$BAFE`   | `DIV10`      | NOT DONE | divide FAC1 by 10, result is always positive       |
 | `$BB0F`   | `FDIV`       | PARTIAL  | needs `FDIVT`                                      |
 | `$BB12`   | `FDIVT`      | NOT DONE | divide FAC2 by FAC1, ignores sign                  |
-| `$BBA2`   | `MOVFM`      | NOT DONE | fetch FAC1 from RAM location                       |
+| `$BBA2`   | `MOVFM`      | PARTIAL  | not fully tested yet                               |
 | `$BBD4`   | `MOVMF`      | NOT DONE | copy FAC1 to memory location, rounds if asked      |
 | `$BBFC`   | `MOVEF`      | NOT DONE | copy FAC2 to FAC1                                  |
 | `$BC0F`   | `MOVFA`      | NOT DONE | copy FAC1 to FAC2, skips rounding                  |

c64/basic/,stubs_math/b853.FSUBT.s

@@ -9,7 +9,7 @@
 // - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
 //
 // Note:
-// - load FAC2 after FAC1, or mimic the Kernals sign comparison
+// - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
 //
 // See also:
 // - [CM64] Computes Mapping the Commodore 64 - page 112

c64/basic/,stubs_math/b86a.FADDT.s

@@ -9,7 +9,7 @@
 // - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
 //
 // Note:
-// - load FAC2 after FAC1, or mimic the Kernals sign comparison
+// - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
 //
 // See also:
 // - [CM64] Computes Mapping the Commodore 64 - page 112

c64/basic/,stubs_math/ba2b.FMULT.s

@@ -9,7 +9,7 @@
 // - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
 //
 // Note:
-// - load FAC2 after FAC1, or mimic the Kernals sign comparison
+// - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
 //
 // See also:
 // - [CM64] Computes Mapping the Commodore 64 - page 113 XXX address does not match

c64/basic/,stubs_math/bba2.MOVFM.s

@@ -1,25 +0,0 @@
-// #LAYOUT# STD *       #TAKE
-// #LAYOUT# *   BASIC_0 #TAKE
-// #LAYOUT# *   *       #IGNORE
-
-//
-// Math package - copy FAC1 to memory location, rounds if asked
-//
-// Input:
-// - .X - address low byte
-// - .Y - address high byte
-// - $70 - if MSB is set performs rouding
-//
-// Output:
-// - .A - FAC1 exponent
-//
-// See also:
-// - [CM64] Computes Mapping the Commodore 64 - page 114
-// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-// - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-//
-
-// XXX provide implementation
-
-MOVMF:
-	STUB_IMPLEMENTATION()

c64/basic/,stubs_math/bbd4.MOVMF.s

@@ -3,17 +3,18 @@
 // #LAYOUT# *   *       #IGNORE
 
 //
-// Math package - fetch FAC1 from RAM location
+// Math package - copy FAC1 to memory location, rounds if asked
 //
 // Input:
-// - .A - address low byte
+// - .X - address low byte
 // - .Y - address high byte
+// - $70 - if MSB is set performs rouding
 //
 // Output:
-// - .A - FAC1 exponent, affects status flags
+// - .A - FAC1 exponent
-// - .Y - always 0
 //
 // See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 114
 // - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //

c64/basic/,stubs_math/bf7b.FPWRT.s

@@ -9,7 +9,7 @@
 // - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
 //
 // Note:
-// - load FAC2 after FAC1, or mimic the Kernals sign comparison
+// - load FAC2 after FAC1, or mimic the Kernals sign comparison (XXX do we need it?)
 // - uses exp(x*log(y)) formula to calculate y^x; slow and inaccurate
 //
 // See also:

c64/basic/math/ba8c.CONUPK.s

@@ -11,10 +11,10 @@
 //
 // Output:
 // - .A - FAC1 exponent (yes, really - Codebase64 is right)
-// - .Y - XXX 0?
+// - .Y - 0 (experimentation with original ROM)
 //
 // Preserves:
-// - .X - (experimentation with original routine)
+// - .X - (experimentation with original ROM)
 //
 // See also:
 // - [CM64] Computes Mapping the Commodore 64 - page 114
@@ -26,11 +26,11 @@
 
 CONUPK:
 
-	// Not sure which temporary variables are used for storage by the original ROMs,
+	// Checked in the available documentation:
-	// but $22/$23 (INDEX+0 and INDEX+1) seem to be good candidates, at least some
-	// math routines use them as pointer storage, see:
 	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
 	// - https://www.lemon64.com/forum/viewtopic.php?t=67576&sid=d41e77cdddd28d6f9c9d52ce5b4e8dc3
+	// that $22/$23 (INDEX+0 and INDEX+1) are at least sometimes used for pointer storage.
+	// Confirmed by experimenting with original ROM that this is the case here too.
 
 	sty INDEX+1
 	sta INDEX+0
@@ -38,8 +38,6 @@ CONUPK:
 	// Now copy the data from RAM to FAC2, for the format description see:
 	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic#Representation_in_the_C-64
 
-	ldy #$04
-
 	// Copy the mantissa - reverse byte order
 
 	ldy #$04

c64/basic/math/bba2.MOVFM.s

@@ -2,35 +2,32 @@
 // #LAYOUT# *   BASIC_0 #TAKE
 // #LAYOUT# *   *       #IGNORE
 
-//
+// Math package - fetch FAC1 from RAM location
-// Math package - fetch FAC2 from RAM location
 //
 // Input:
 // - .A - address low byte
 // - .Y - address high byte
 //
 // Output:
-// - .A - FAC1 exponent (yes, really - Codebase64 is right)
+// - .A - FAC1 exponent, affects status flags
-// - .Y - 0 (tested with original ROMs)
+// - .Y - always 0
 //
 // Preserves:
-// - .X (tested with original ROMs)
+// - .X - (experimentation with original ROM)
 //
 // See also:
-// - [CM64] Computes Mapping the Commodore 64 - page 114
 // - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-//
 
 // XXX test this
 
-CONUPK:
+MOVMF:
 
-	// Noticed in the avilable materials:
+	// Checked in the available documentation:
 	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
 	// - https://www.lemon64.com/forum/viewtopic.php?t=67576&sid=d41e77cdddd28d6f9c9d52ce5b4e8dc3
-	// that at least some math routines use $22/$23 (INDEX+0 and INDEX+1) for pointer storage,
+	// that $22/$23 (INDEX+0 and INDEX+1) are at least sometimes used for pointer storage.
-	// confirmed that this routine is not an exception
+	// Confirmed by experimenting with original ROM that this is the case here too.
 
 	sty INDEX+1
 	sta INDEX+0
@@ -38,26 +35,24 @@ CONUPK:
 	// Now copy the data from RAM to FAC2, for the format description see:
 	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic#Representation_in_the_C-64
 
-	ldy #$04
-
 	// Copy the mantissa - reverse byte order
 
 	ldy #$04
 	lda (INDEX), y
-	sta FAC2_mantissa+3
+	sta FAC1_mantissa+3
 
 	dey
 	lda (INDEX), y
-	sta FAC2_mantissa+2
+	sta FAC1_mantissa+2
 
 	dey
 	lda (INDEX), y
-	sta FAC2_mantissa+1
+	sta FAC1_mantissa+1
 
 	dey
 	lda (INDEX), y
 	ora #$80                           // clear the sign bit
-	sta FAC2_mantissa+0
+	sta FAC1_mantissa+0
 
 	// Copy the sign
 
@@ -68,13 +63,21 @@ CONUPK:
 !:
 	lda $00
 
-	sta FAC2_sign
+	sta FAC1_sign
 
 	// Copy the exponent
 
 	dey
 	lda (INDEX), y
-	sta FAC2_exponent
+	sta FAC1_exponent
+
+	// Set low order mantissa - to my surprise original ROM seems to put 0 to FACOW - XXX why???
+	// Since we do not know the original value (lost due to variable format having one byte shorter
+    // mantissa than FAC1), it is probably best to put some approximate value here; putting $80
+    // would be risky in case rouding is performed later, $7F seems to be sane choice
+
+	lda #$7F
+	sta FACOV
 
 	// Return the FAC1 exponent