From 5a3f65efa4b1aa505b7928f85749612de2ef29bc Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Tue, 1 Apr 2025 19:40:04 +0200
Subject: [PATCH] Add get_FAC1_via_INDEX

Also change to only use bit 7 as sign in FAC1 and FAC2 (as the original BASIC does) to simplify
implementations.
---
 STATUS.md                                     |  2 +-
 .../,stubs_math/bba6.get_FAC1_via_INDEX.s     | 17 ----
 src/basic/math/FCOMP.s                        | 26 +++---
 src/basic/math/bc2b.sgn_FAC1_A.s              |  6 +-
 src/basic/math_mov/ba90.get_FAC2_via_INDEX.s  | 12 +--
 src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s    |  8 --
 src/basic/math_mov/bba2.mov_MEM_FAC1.s        | 30 +++++++
 src/basic/math_mov/bba6.get_FAC1_via_INDEX.s  | 45 +++++++++++
 .../{,stubs_math => math_mov}/bba6.interop    |  0
 src/basic/math_mov/mov_MEM_FAC1.s             | 79 -------------------
 ...B122856388B12285660980856288B1228561847060 |  3 +
 strings/20A2BB4C                              |  3 +
 strings/60202BBC85                            |  5 ++
 strings/6E0980856A88B1228569A56160            |  3 +
 ...A004B122856D88B122856C88B122856B88B122856E |  3 +
 strings/A9A8A0AE20A2BB4C                      |  3 +
 strings/B124456630                            |  3 +
 testsuite/unit/math.vs                        | 16 +++-
 18 files changed, 130 insertions(+), 134 deletions(-)
 delete mode 100644 src/basic/,stubs_math/bba6.get_FAC1_via_INDEX.s
 delete mode 100644 src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s
 create mode 100644 src/basic/math_mov/bba2.mov_MEM_FAC1.s
 create mode 100644 src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
 rename src/basic/{,stubs_math => math_mov}/bba6.interop (100%)
 delete mode 100644 src/basic/math_mov/mov_MEM_FAC1.s
 create mode 100644 strings/04B122856588B122856488B122856388B12285660980856288B1228561847060
 create mode 100644 strings/20A2BB4C
 create mode 100644 strings/60202BBC85
 create mode 100644 strings/6E0980856A88B1228569A56160
 create mode 100644 strings/A004B122856D88B122856C88B122856B88B122856E
 create mode 100644 strings/A9A8A0AE20A2BB4C
 create mode 100644 strings/B124456630

diff --git a/STATUS.md b/STATUS.md
index 422b7e4c..53bab291 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -222,7 +222,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BB0F`   | `div_MEM_FAC1`         | DONE     |                                                    |
 | `$BB12`   | `div_FAC2_FAC1`        | DONE     |                                                    |
 | `$BBA2`   | `mov_MEM_FAC1`         | DONE     |                                                    |
-| `$BBA6`   | `get_FAC2_via_INDEX`   | NOT DONE |                                                    |
+| `$BBA6`   | `get_FAC1_via_INDEX`   | DONE     |                                                    |
 | `$BBC7`   | `mov_r_FAC1_TMP2`      | PARTIAL  | not fully tested yet                               |
 | `$BBCA`   | `mov_r_FAC1_TMP1`      | PARTIAL  | not fully tested yet                               |
 | `$BBD0`   | `mov_r_FAC1_VAR`       | PARTIAL  | not fully tested yet                               |
diff --git a/src/basic/,stubs_math/bba6.get_FAC1_via_INDEX.s b/src/basic/,stubs_math/bba6.get_FAC1_via_INDEX.s
deleted file mode 100644
index 81499d2f..00000000
--- a/src/basic/,stubs_math/bba6.get_FAC1_via_INDEX.s
+++ /dev/null
@@ -1,17 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - XXX
-;
-; See also:
-; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
-;
-
-; XXX implement, test
-
-get_FAC1_via_INDEX:
-
-	+STUB_IMPLEMENTATION
diff --git a/src/basic/math/FCOMP.s b/src/basic/math/FCOMP.s
index f127dd4c..1a754efd 100644
--- a/src/basic/math/FCOMP.s
+++ b/src/basic/math/FCOMP.s
@@ -32,11 +32,9 @@ FCOMP:
     php
 
     ldy #$01
-    lda #$7F                ; Expand sign of RAM float into A as $FF or $00
-    cmp (INDEX+2),Y
-    adc #$80
-    cmp FAC1_sign
-    bne FCOMP_greater_than  ; FAC < or > RAM, will be swapped to correct
+    lda (INDEX+2),Y
+    eor FAC1_sign           ; Check if signs are different
+    bmi FCOMP_greater_than  ; FAC < or > RAM, will be swapped to correct
 
     dey
     lda (INDEX+2),Y         ; Exponent of RAM float into A
@@ -76,17 +74,17 @@ FCOMP_equal:
 
 
 FCOMP_less_than:
-    lda #$FF
-    cmp FAC1_sign
-    bne @1
+    lda FAC1_sign
+    bpl FCOMP_FF
+FCOMP_01:
     lda #$01
-@1: plp
+    plp
     rts
-
+    
 FCOMP_greater_than:
-    lda #$01
-    cmp FAC1_sign
-    bcs @1
+    lda FAC1_sign
+    bpl FCOMP_01
+FCOMP_FF:
     lda #$FF
-@1: plp
+    plp
     rts
diff --git a/src/basic/math/bc2b.sgn_FAC1_A.s b/src/basic/math/bc2b.sgn_FAC1_A.s
index 0fb477ce..27b10ab6 100644
--- a/src/basic/math/bc2b.sgn_FAC1_A.s
+++ b/src/basic/math/bc2b.sgn_FAC1_A.s
@@ -20,7 +20,11 @@ sgn_FAC1_A:
 	lda FAC1_exponent
 	beq @1
 	lda FAC1_sign
-	bne @1
+	bmi @2
 	lda #$01
 @1:
 	rts
+	
+@2:
+    lda #$FF
+    rts
diff --git a/src/basic/math_mov/ba90.get_FAC2_via_INDEX.s b/src/basic/math_mov/ba90.get_FAC2_via_INDEX.s
index 508005f3..4b135a21 100644
--- a/src/basic/math_mov/ba90.get_FAC2_via_INDEX.s
+++ b/src/basic/math_mov/ba90.get_FAC2_via_INDEX.s
@@ -33,20 +33,10 @@ get_FAC2_via_INDEX:
 
 	dey
 	lda (INDEX), y
+	sta FAC2_sign
 	ora #$80                           ; clear the sign bit
 	sta FAC2_mantissa+0
 
-	; Copy the sign
-
-	lda (INDEX), y
-	bpl @1                             ; assumption: non-negative numbers are more frequent
-	lda #$FF
-	+skip_2_bytes_trash_nvz
-@1:
-	lda #$00
-
-	sta FAC2_sign
-
 	; Copy the exponent
 
 	dey
diff --git a/src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s b/src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s
deleted file mode 100644
index bad7d253..00000000
--- a/src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s
+++ /dev/null
@@ -1,8 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-; Just a compatibility jump - our routine is longer than original one
-
-	jmp mov_MEM_FAC1
diff --git a/src/basic/math_mov/bba2.mov_MEM_FAC1.s b/src/basic/math_mov/bba2.mov_MEM_FAC1.s
new file mode 100644
index 00000000..4843ff8f
--- /dev/null
+++ b/src/basic/math_mov/bba2.mov_MEM_FAC1.s
@@ -0,0 +1,30 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+
+; Math package - fetch FAC1 from RAM location
+;
+; Input:
+; - .A - address low byte
+; - .Y - address high byte
+;
+; Output:
+; - .A - FAC1 exponent, affects status flags
+; - .Y - always 0
+;
+; Preserves:
+; - .X - (experimentation with original ROM)
+;
+; See also:
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+
+
+
+mov_MEM_FAC1:
+	sty INDEX+1
+	sta INDEX+0
+
+    ; FALLTHROUGH to get_FAC1_via_INDEX
diff --git a/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s b/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
new file mode 100644
index 00000000..cb29efa2
--- /dev/null
+++ b/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
@@ -0,0 +1,45 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+; Math package - Mov MEM to FAC1 with address in INDEX zero page register
+;
+; See also:
+; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
+;
+
+get_FAC1_via_INDEX:
+
+	; Copy the mantissa
+
+	ldy #$04
+	lda (INDEX), y
+	sta FAC1_mantissa+3
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+2
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+1
+
+	dey
+	lda (INDEX), y
+	sta FAC1_sign
+	ora #$80                           ; clear the sign bit
+	sta FAC1_mantissa+0
+
+	; Copy the exponent
+
+	dey
+	lda (INDEX), y
+	sta FAC1_exponent
+
+	; Set low order mantissa to 0 - this should give the
+	; most precision while operating on integers
+
+	sty FACOV
+
+	rts
diff --git a/src/basic/,stubs_math/bba6.interop b/src/basic/math_mov/bba6.interop
similarity index 100%
rename from src/basic/,stubs_math/bba6.interop
rename to src/basic/math_mov/bba6.interop
diff --git a/src/basic/math_mov/mov_MEM_FAC1.s b/src/basic/math_mov/mov_MEM_FAC1.s
deleted file mode 100644
index 94ec6ad7..00000000
--- a/src/basic/math_mov/mov_MEM_FAC1.s
+++ /dev/null
@@ -1,79 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-; Math package - fetch FAC1 from RAM location
-;
-; Input:
-; - .A - address low byte
-; - .Y - address high byte
-;
-; Output:
-; - .A - FAC1 exponent, affects status flags
-; - .Y - always 0
-;
-; Preserves:
-; - .X - (experimentation with original ROM)
-;
-; See also:
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-
-; XXX test this
-
-mov_MEM_FAC1:
-
-	; Original routines use $22/$23 location for a vector too, see here:
-	; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-
-	sty INDEX+1
-	sta INDEX+0
-
-	; 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
-
-	; Copy the mantissa
-
-	ldy #$04
-	lda (INDEX), y
-	sta FAC1_mantissa+3
-
-	dey
-	lda (INDEX), y
-	sta FAC1_mantissa+2
-
-	dey
-	lda (INDEX), y
-	sta FAC1_mantissa+1
-
-	dey
-	lda (INDEX), y
-	ora #$80                           ; clear the sign bit
-	sta FAC1_mantissa+0
-
-	; Copy the sign
-
-	lda (INDEX), y
-	bpl @1                             ; assumption: non-negative numbers are more frequent
-	lda #$FF
-	+skip_2_bytes_trash_nvz
-@1:
-	lda #$00
-
-	sta FAC1_sign
-
-	; Copy the exponent
-
-	dey
-	lda (INDEX), y
-	sta FAC1_exponent
-
-	; Set low order mantissa to 0 - this should give the
-	; most precision while operating on integers
-
-	sty FACOV
-
-	; Return the FAC1 exponent
-
-	lda FAC1_exponent
-	rts
diff --git a/strings/04B122856588B122856488B122856388B12285660980856288B1228561847060 b/strings/04B122856588B122856488B122856388B12285660980856288B1228561847060
new file mode 100644
index 00000000..04019ec9
--- /dev/null
+++ b/strings/04B122856588B122856488B122856388B12285660980856288B1228561847060
@@ -0,0 +1,3 @@
+$04 + LDA ($22),Y + STA $65 + DEY + LDA ($22),Y + STA $64 + DEY + LDA ($22),Y + STA $63 + DEY + LDA ($22),Y + STA $66 + ORA #$80 + STA $62 + DEY + LDA ($22),Y + STA $61 + STY $70 + RTS
+
+Load FAC1 (well known zero page locations) from memory using well known vector in zero page (INDEX)
diff --git a/strings/20A2BB4C b/strings/20A2BB4C
new file mode 100644
index 00000000..77ad0c4f
--- /dev/null
+++ b/strings/20A2BB4C
@@ -0,0 +1,3 @@
+JSR $BBA2 + JMP fragment
+
+Call to well known floating point function + fragment
diff --git a/strings/60202BBC85 b/strings/60202BBC85
new file mode 100644
index 00000000..f29efa39
--- /dev/null
+++ b/strings/60202BBC85
@@ -0,0 +1,5 @@
+60 20 2B BC 85
+
+RTS + JSR $BC2B + STA fragment
+
+Fragments + call to well known floating point function
diff --git a/strings/6E0980856A88B1228569A56160 b/strings/6E0980856A88B1228569A56160
new file mode 100644
index 00000000..d894ad6e
--- /dev/null
+++ b/strings/6E0980856A88B1228569A56160
@@ -0,0 +1,3 @@
+$6E + ORA #$80 + STA $6A + DEY + LDA ($22),Y + STA $69 + LDA $61 + RTS
+
+Fragment of copying using a well known index vector from a mem float into FAC2
diff --git a/strings/A004B122856D88B122856C88B122856B88B122856E b/strings/A004B122856D88B122856C88B122856B88B122856E
new file mode 100644
index 00000000..c4f5496e
--- /dev/null
+++ b/strings/A004B122856D88B122856C88B122856B88B122856E
@@ -0,0 +1,3 @@
+LDY #$04 + LDA ($22),Y + STA $6D +  DEY + LDA ($22),Y + STA $6C + DEY + LDA ($22),Y + STA $6B + DEY + LDA ($22),Y + STA $6E
+
+Load parts of the mantissa of FAC2 and its sign (well known zero page locations) from memory using well known vector in zero page (INDEX)
diff --git a/strings/A9A8A0AE20A2BB4C b/strings/A9A8A0AE20A2BB4C
new file mode 100644
index 00000000..56912c73
--- /dev/null
+++ b/strings/A9A8A0AE20A2BB4C
@@ -0,0 +1,3 @@
+LDA #$A8 + LDY #$AE + JSR $BBA2 + JMP fragment
+
+Loading well known address of math constant pi into AY and call well known floating point function (mov_MEM_FAC1)
diff --git a/strings/B124456630 b/strings/B124456630
new file mode 100644
index 00000000..af510266
--- /dev/null
+++ b/strings/B124456630
@@ -0,0 +1,3 @@
+LDA ($24),Y + EOR $66 + BMI fragment
+
+Compare signs of FAC1 and float pointed to by index vector
diff --git a/testsuite/unit/math.vs b/testsuite/unit/math.vs
index 410aa3cb..d86a3330 100644
--- a/testsuite/unit/math.vs
+++ b/testsuite/unit/math.vs
@@ -139,12 +139,22 @@ r A=$E0
 r Y=$B9
 r PC=$BBA2
 ret
-fill $1001 $1006 80 80 00 00 00 FF
+fill $1001 $1006 80 80 00 00 00 80
 print "COMPARE"
 compare $61 $66 $1001
 compare $70 $70 $1003  ; FACOV = 0
 print "END"
 
+print "TEST: get_FAC1_via_INDEX -0.5"
+fill $61 $66 FF FF FF FF FF AA
+fill $22 $23 E0 B9
+r PC=$BBA6
+ret
+fill $1001 $1006 80 80 00 00 00 80
+print "COMPARE"
+compare $61 $66 $1001
+print "END"
+
 print "TEST: mov MEM FAC2 const 1.0"
 fill $69 $6E FF FF FF FF FF AA
 r A=$BC
@@ -162,7 +172,7 @@ r A=$E0
 r Y=$B9
 r PC=$BA8C
 ret
-fill $1001 $1006 80 80 00 00 00 FF
+fill $1001 $1006 80 80 00 00 00 80
 print "COMPARE"
 compare $69 $6E $1001
 print "END"
@@ -172,7 +182,7 @@ fill $69 $6E FF FF FF FF FF AA
 fill $22 $23 E0 B9
 r PC=$BA90
 ret
-fill $1001 $1006 80 80 00 00 00 FF
+fill $1001 $1006 80 80 00 00 00 80
 print "COMPARE"
 compare $69 $6E $1001
 print "END"